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Current papers in developmental biology and gene function





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Tuesday, February 21st

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Wehr Mathews, K., Cavegn, M. and Zwicky, M. (2017). Sexual dimorphism of body size is controlled by dosage of the X-chromosomal gene Myc and by the sex-determining gene tra in Drosophila. Genetics [Epub ahead of print]. PubMed ID: 28064166
Summary:
Drosophila females are larger than males. This paper describes how X chromosome dosage drives sexual dimorphism of body size through two means: first, through unbalanced expression of a key X-linked growth regulating gene and second, through female-specific activation of the sex-determination pathway. X-chromosome dosage determines phenotypic sex by regulating the genes of the sex-determining pathway. In the presence of two sets of X-chromosome signal elements (XSEs), Sex-lethal (Sxl) is activated in female (XX) but not male (XY) animals. Sxl activates transformer (tra), a gene that encodes a splicing factor essential for female-specific development. It has previously been shown that null mutations in the tra gene result in only a partial reduction of body size of XX animals, which shows that other factors must contribute to size determination. Whether X dosage directly affects animal size was tested by analyzing males with duplications of X chromosomal segments. Upon tiling across the X chromosome, four duplications were found that increase male size by over 9%. Only one of these, Myc, was found not to be dosage compensated. Together, these results indicate that both Myc dosage and tra expression play crucial roles in determining sex-specific size in Drosophila larvae and adult tissue. Since Myc also acts as an XSE that contributes to tra activation in early, development, a double dose of Myc in females serves at least twice in development to promote sexual size dimorphism.
Fumey, J. and Wicker-Thomas, C. (2017). Mutations at the Darkener of Apricot locus modulate pheromone production and sex behavior in Drosophila melanogaster. J Insect Physiol [Epub ahead of print]. PubMed ID: 28088352
Summary:
Mutations at the Darkener of Apricot (Doa) locus of Drosophila melanogaster alter sexual differentiation by disrupting sex-specific splicing of doublesex pre-mRNA, a key regulator of sex determination. This paper examined the effect of seven Doa alleles and several trans-heterozygous combinations on pheromones and courtship behavior . The cuticular hydrocarbon (CHC) profile was slightly masculinized in females, with an accumulation of shorter compounds (C23 and C25) and a reduction in longer compounds (C27 and C29). The profile was feminized in males. Female cuticular profiles showed fewer dienes and female pheromones in six alleles and in the trans-heterozygotes and showed more male pheromones (tricosene and pentacosene) in three alleles (DEM, E786 and HD) and in all trans-heterozygotes. Courtship was severely affected in Doa males; in particular, males made fewer copulation attempts and copulated less with both control and Doa females. These results suggest that Doa could modulate pheromone production and sex behavior by altering sexual differentiation in the cuticle and the nervous system.
Ohhara, Y., Kobayashi, S. and Yamanaka, N. (2017). Nutrient-dependent endocycling in steroidogenic tissue dictates timing of metamorphosis in Drosophila melanogaster. PLoS Genet 13: e1006583. PubMed ID: 28121986
Summary:
Many animals have an intrinsic growth checkpoint during juvenile development, after which an irreversible decision is made to upregulate steroidogenesis, triggering the metamorphic juvenile-to-adult transition. However, a molecular process underlying such a critical developmental decision remains obscure. This study shows that nutrient-dependent endocycling in steroidogenic cells provides the machinery necessary for irreversible activation of metamorphosis in Drosophila melanogaster. Endocycle progression in cells of the prothoracic gland (PG) is tightly coupled with the growth checkpoint, and block of endocycle in PG cells causes larval developmental arrest due to reduction in biosynthesis of the steroid hormone ecdysone. Moreover, inhibition of the nutrient sensor target of rapamycin (TOR) in the PG during the checkpoint period causes endocycle inhibition and developmental arrest, which can be rescued by inducing additional rounds of endocycles by Cyclin E. The study proposes that a TOR-mediated cell cycle checkpoint in steroidogenic tissue provides a systemic growth checkpoint for reproductive maturation.

Saiz-Lopez, P., Chinnaiya, K., Towers, M. and Ros, M. A. (2017). Intrinsic properties of limb bud cells can be differentially reset. Development [Epub ahead of print]. PubMed ID: 28087638
Evolutionary Homolog Study
An intrinsic timing mechanism specifies the positional values of the zeugopod (i.e. radius/ulna) and then autopod (i.e. wrist/digits) segments during limb development. This study addressed if this timing mechanism ensures that patterning events occur only once by grafting GFP-expressing autopod progenitor cells to the earlier host signaling environment of zeugopod progenitor cells. Early and late autopod progenitors fated for the wrist and phalanges, respectively, both contribute to the entire host autopod indicating that the autopod positional value is irreversibly determined as revealed by Hoxa13 (see Drosophila AbdominaB) expression. Evidence is provided that Hoxa13 provides an autopod-specific positional value that correctly allocates cells into the autopod, most likely through the control of cell-surface properties as shown by cell-cell sorting analyses. However, only the earlier autopod cells can adopt the host proliferation rate to permit normal morphogenesis. Therefore, these findings reveal that the ability of embryonic cells to differentially reset their intrinsic behaviors confers robustness to limb morphogenesis. It is speculated that this plasticity could be maintained beyond embryogenesis in limbs with regenerative capacity.

Monday, February 20th

McElroy, K. A., Jung, Y. L., Zee, B. M., Wang, C. I., Park, P. J. and Kuroda, M. I. (2017). upSET, the Drosophila homologue of SET3, Is required for viability and the proper balance of active and repressive chromatin marks. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 28064188
Summary:
Chromatin plays a critical role in faithful implementation of gene expression programs. Different post-translational modifications of histone proteins reflect the underlying state of gene activity, and many chromatin proteins write, erase, bind, or are repelled by these histone marks. One such protein is UpSET, the Drosophila homolog of yeast Set3 and mammalian KMT2E (MLL5). This study shows that UpSET is necessary for the proper balance between active and repressed states. Using CRISPR/Cas-9 editing, S2 cells were generated that are mutant for upset. Loss of UpSET was tolerated in S2 cells, but heterochromatin is misregulated, as evidenced by a strong decrease in H3K9me2 levels assessed by bulk histone post-translational modification quantification. To test whether this finding was consistent in the whole organism, the upset coding sequence was deleted using CRISPR/Cas-9; it was found to be lethal in both sexes in flies. This lethality could be rescued using a tagged upSET transgene; UpSET protein was found to localizes to transcriptional start sites of active genes throughout the genome. Misregulated heterochromatin is apparent by suppressed position effect variegation of a wm4 allele in heterozygous upset-deleted flies. This result applies to heterochromatin genes generally using nascent-RNA sequencing in the upset-mutant S2 lines. These findings support a critical role for UpSET in maintaining heterochromatin, perhaps by delimiting the active chromatin environment.
Falahati, H. and Wieschaus, E. (2017). Independent active and thermodynamic processes govern the nucleolus assembly in vivo. Proc Natl Acad Sci U S A 114(6): 1335-1340. PubMed ID: 28115706
Summary:
Membraneless organelles play a central role in the organization of protoplasm by concentrating macromolecules, which allows efficient cellular processes. Recent studies have shown that, in vitro, certain components in such organelles can assemble through phase separation. Inside the cell, however, such organelles are multicomponent, with numerous intermolecular interactions that can potentially affect the demixing properties of individual components. In addition, the organelles themselves are inherently active, and it is not clear how the active, energy-consuming processes that occur constantly within such organelles affect the phase separation behavior of the constituent macromolecules. This study examined the phase separation model for the formation of membraneless organelles in vivo by assessing the two features that collectively distinguish it from active assembly, namely temperature dependence and reversibility. A microfluidic device that allows accurate and rapid manipulation of temperature was used, and the quantitative dynamics were examined by which six different nucleolar proteins (Modulo, Fibrillarin, Nucleostemin1, Pitchoune, Nopp140 and Ppl135) assemble into the nucleoli of Drosophila melanogaster embryos. The results indicate that, although phase separation is the main mode of recruitment for four of the studied proteins, the assembly of the other two is irreversible and enhanced at higher temperatures, behaviors indicative of active recruitment to the nucleolus. These two subsets of components differ in their requirements for ribosomal DNA; the two actively assembling components fail to assemble in the absence of ribosomal DNA, whereas the thermodynamically driven components assemble but lose temporal and spatial precision.
Narendra, V., Bulajić, M., Dekker, J., Mazzoni, E.O. and Reinberg, D. (2016). CTCF-mediated topological boundaries during development foster appropriate gene regulation. Genes Dev 30: 2657-2662. PubMed ID: 28087711
Evolutionary Homolog Study:
The genome is organized into repeating topologically associated domains (TADs) (see Drosophila chromatin organization), each of which is spatially isolated from its neighbor by poorly understood boundary elements thought to be conserved across cell types. This study shows that deletion of CTCF (CCCTC-binding factor)-binding sites at TAD and sub-TAD topological boundaries that form within the HoxA (see Drosophila lab) and HoxC (see Drosophila Dfd) clusters during differentiation of mouse embryonic stem cells not only disturbs local chromatin domain organization and regulatory interactions but also results in homeotic transformations typical of Hox gene misregulation. Moreover, CTCF-dependent boundary function can be modulated by competing forces, such as the self-assembly of polycomb domains within the nucleus. Therefore, CTCF boundaries are not merely static structural components of the genome but instead are locally dynamic regulatory structures that control gene expression during development.

Tomaz, R. A., et al. (2017). Jmjd2c/Kdm4c facilitates the assembly of essential enhancer-protein complexes at the onset of embryonic stem cell differentiation. Development [Epub ahead of print]. PubMed ID: 28087629
Evolutionary Homolog Study
Jmjd2/Kdm4 H3K9-demethylases (see Drosophila Kdm4A) cooperate in promoting mouse embryonic stem cell (ESC) identity. However, little is known about their importance at the exit of ESC pluripotency. This study uncovered that Jmjd2c facilitates this process by stabilizing the assembly of Mediator-Cohesin complexes at lineage-specific enhancers. Functionally, Jmjd2c is required in ESCs to initiate appropriate gene expression programs upon somatic multi-lineage differentiation. In the absence of Jmjd2c, differentiation is stalled at an early post-implantation epiblast-like stage, while Jmjd2c-knockout ESCs remain capable of forming extra-embryonic endoderm derivatives. Dissection of the underlying molecular basis revealed that Jmjd2c is re-distributed to lineage-specific enhancers during ESC priming for differentiation. Interestingly, Jmjd2c-bound enhancers are co-occupied by the H3K9-methyltransferase G9a/Ehmt2, independently of its H3K9-modifying activity. Loss of Jmjd2c abrogates G9a recruitment and furthermore destabilizes loading of the Mediator and Cohesin components Med1 and Smc1a at newly activated and poised enhancers in ESC-derived epiblast-like cells. These findings unveil Jmjd2c-G9a as novel enhancer-associated factors, and implicate Jmjd2c as a molecular scaffold for the assembly of essential enhancer-protein complexes with impact on timely gene activation.

Sunday, February 19th

Merigliano, C., Marzio, A., Renda, F., Somma, M.P., Gatti, M. and Vernì, F. (2016). A role for the Twins protein phosphatase (PP2A-B55) in the maintenance of Drosophila genome integrity. Genetics [Epub ahead of print]. PubMed ID: 28040742
Summary:
The protein phosphatase 2A (PP2A) is a conserved heterotrimeric enzyme that is mutated in many types of cancer and acts as a tumor suppressor. In mammalian cells, PP2A inhibition results in DNA double strand breaks (DSBs) and chromosome aberrations (CABs). However, the mechanisms through which PP2A prevents DNA damage are still unclear. This study focuses on the role of the Drosophila twins (tws) gene in the maintenance of chromosome integrity; tws encodes the B regulatory subunit (B/B55) of PP2A. Mutations in tws cause high frequencies of CABs (0.5 CABs/cell) in Drosophila larval brain cells and lead to an abnormal persistence of γ-H2Av repair foci. However, mutations that disrupt the PP4 phosphatase activity impair foci dissolution but do not cause CABs, suggesting that a delayed foci regression is not clastogenic. Tws is required for activation of the G2/M DNA damage checkpoint, while PP4 is required for checkpoint recovery, a result that points to a conserved function of these phosphatases from flies to humans. Mutations in the ATM-coding gene tefu are strictly epistatic to tws mutations for the CAB phenotype, suggesting that failure to dephosphorylate an ATM substrate(s) impairs DNA DSBs repair. In addition, mutations in the Ku70 gene, which do not cause CABs, completely suppress CAB formation in tws Ku70 double mutants. These results suggest the hypothesis that an improperly phosphorylated Ku70 protein can lead to DNA damage and CABs.
Sha, Q. Q., Dai, X. X., Dang, Y., Tang, F., Liu, J., Zhang, Y. L. and Fan, H. Y. (2016). MAPK cascade couples maternal mRNA translation and degradation to meiotic cell cycle progression in mouse oocyte. Development. PubMed ID: 27993988
Evolutionary Homolog Study

Mammalian oocyte maturation depends on the translational activation of stored maternal mRNAs upon meiotic resumption. Cytoplasmic polyadenylation element binding protein-1 (CPEB1; see Drosophila Orb2) is a key oocyte factor that regulates maternal mRNA translation. However, the signal that triggers CPEB1 activation at the onset of mammalian oocyte maturation is not known. This study provides evidence that a mitogen-activated protein kinase (MAPK) cascade couples maternal mRNA translation to meiotic cell cycle progression in mouse oocytes, by triggering CPEB1 phosphorylation and degradation. Mutations of the phosphorylation sites or ubiquitin E3 ligase binding sites in CPEB1 have a dominant negative effect in oocytes, and mimic the phenotype of ERK1/2 (see Drosophila Rolled) knockout, by impairing spindle assembly and mRNA translation. Overexpression of the CPEB1-downstream translation activator DAZL (see Drosophila Boule) in ERK1/2-deficient oocytes partially rescued the meiotic defects, indicating that ERK1/2 is essential for spindle assembly, metaphase II arrest, and maternal-zygotic transition (MZT) primarily by triggering the translation of key maternal mRNAs. Taken together, ERK1/2-mediated CPEB1 phosphorylation/degradation is a major mechanism of maternal mRNA translational activation, and is crucial for mouse oocyte maturation and MZT.

Peel, N., Iyer, J., Naik, A., Dougherty, M.P., Decker, M. and O'Connell, K.F. (2017). Protein phosphatase 1 down regulates ZYG-1 levels to limit centriole duplication. PLoS Genet [Epub ahead of print]. PubMed ID: 28103229
Evolutionary Homolog Study:
In humans perturbations of centriole number are associated with tumorigenesis and microcephaly, therefore appropriate regulation of centriole duplication is critical. The C. elegans homolog of Plk4, ZYG-1 (see Drosophila SAK), is required for centriole duplication, but the understanding of how ZYG-1 levels are regulated remains incomplete. This study identified the two PP1 orthologs, GSP-1 (see Drosophila flw) and GSP-2 (see Drosophila Pp1-87B), and their regulators I-2SZY-2 (see Drosophila I-2) and SDS-22 (see Drosophila sds22) as key regulators of ZYG-1 protein levels. Down-regulation of PP1 activity either directly, or by mutation of szy-2 or sds-22 can rescue the loss of centriole duplication (see Drosophila centrioles) associated with a zyg-1 hypomorphic allele. Suppression is achieved through an increase in ZYG-1 levels, and data indicate that PP1 normally regulates ZYG-1 through a post-translational mechanism. While moderate inhibition of PP1 activity can restore centriole duplication to a zyg-1 mutant, strong inhibition of PP1 in a wild-type background leads to centriole amplification via the production of more than one daughter centriole. These results thus define a new pathway that limits the number of daughter centrioles produced each cycle.

Ribeiro, A. L., Silva, R. D., Foyn, H., Tiago, M. N., Rathore, O. S., Arnesen, T. and Martinho, R. G. (2016). Naa50/San-dependent N-terminal acetylation of Scc1 is potentially important for sister chromatid cohesion. Sci Rep 6: 39118. PubMed ID: 27996020
Summary:
The gene separation anxiety (san) encodes Naa50/San, a N-terminal acetyltransferase required for chromosome segregation during mitosis. Although highly conserved among higher eukaryotes, the mitotic function of this enzyme is still poorly understood. Naa50/San was originally proposed to be required for centromeric sister chromatid cohesion in Drosophila and human cells, yet, more recently, it was also suggested to be a negative regulator of microtubule polymerization through internal acetylation of beta Tubulin. This study used genetic and biochemical approaches to clarify the function of Naa50/San during development. The work suggests that Naa50/San is required during tissue proliferation for the correct interaction between the subunits Scc1 and Smc3. The results also suggest a working model where Naa50/San N-terminally acetylates the nascent Scc1 polypeptide, and that this co-translational modification is subsequently required for the establishment and/or maintenance of sister chromatid cohesion.

Saturday, February 18th

Jeibmann, A., Schulz, J., Eikmeier, K., Johann, P.D., Thiel, K., Tegeder, I., Ambrée, O., Frühwald, M.C., Pfister, S.M., Kool, M., Paulus, W. and Hasselblatt, M. (2017). SMAD dependent signaling plays a detrimental role in a fly model of SMARCB1-deficiency and the biology of atypical teratoid/rhabdoid tumors. J Neurooncol [Epub ahead of print]. PubMed ID: 28108836
Summary:
Atypical teratoid/rhabdoid tumors (ATRT) are highly malignant brain tumors arising in young children. The majority of ATRT is characterized by inactivation of the chromatin remodeling complex member SMARCB1 (INI1/hSNF5). Little is known, however, on downstream pathways involved in the detrimental effects of SMARCB1 deficiency which might also represent targets for treatment. Using Drosophila melanogaster and the Gal4-UAS system, modifier screens were performed in this study in order to identify the role of SMAD dependent signaling in the lethal phenotype associated with knockdown of snr1, the fly homolog of SMARCB1. Expression and functional role of human homologs was next investigated in ATRT tumor samples and SMARCB1-deficient rhabdoid tumor cells. The lethal phenotype associated with snr1 knockdown in Drosophila melanogaster could be shifted to later stages of development upon additional knockdown of several decapentaplegic pathway members including Smox, and Med. Similarly, the transforming growth factor beta (TGFbeta) receptor type I kinase inhibitor SB431542 was found to ameliorate the detrimental effect of snr1 knockdown in the fruit fly. Examination of homologs of candidate decapentaplegic pathway members in human SMARCB1-deficent ATRT samples reveal SMAD3 and SMAD6 to be over-expressed. In SMARCB1-deficent rhabdoid tumor cells, siRNA-mediated silencing of SMAD3 or SMAD6 expression reduces TGFbeta signaling activity and results in decreased proliferation. Similar results are obtained upon pharmacological inhibition of TGFbeta signaling using SB431542. These data suggest that SMAD dependent signaling is involved in the detrimental effects of SMARCB1-deficiency and provide a rationale for the investigation of TGFbeta targeted treatments in ATRT.

Abekhoukh, S., Sahin, H. B., Grossi, M., Zongaro, S., Maurin, T., Madrigal, I., Kazue-Sugioka, D., Raas-Rothschild, A., Doulazmi, M., Carrera, P., Stachon, A., Scherer, S., Nascimento, M. R., Trembleau, A., Arroyo, I., Peter, S., Smith, I. M., Mila, M., Smith, A. C., Giangrande, A., Caille, I. and Bardoni, B. (2017). New insights into the regulatory function of CYFIP1 in the context of WAVE- and FMRP-containing complexes. Dis Model Mech [Epub ahead of print]. PubMed ID: 28183735
Summary:
CYtoplasmic FMRP Interacting Protein 1 (CYFIP1) is a candidate gene for intellectual disability (ID), autism, schizophrenia and epilepsy. It is a member of a family of proteins that is very conserved during evolution, sharing high homology with dCYFIP, its Drosophila homolog. CYFIP1 interacts with the Fragile X Mental Retardation Protein (FMRP), whose absence causes the Fragile X Syndrome, and with the translation initiation factor eIF4E. It is a member of the WAVE Regulatory Complex (WRC), thus representing a link between translational regulation and actin cytoskeleton. Data is presented showing a correlation between mRNA levels of CYFIP1 and other members of the WRC. This suggests a tight regulation of the levels of the WRC members not only by post-translational mechanisms, as previously hypothesized. Moreover, the impact of loss of function of both CYFIP1 and FMRP on neuronal growth and differentiation in was studied in two animal models, fly and mouse. These two proteins antagonize each other's function not only during neuromuscular junction growth in the fly but also during new neuronal differentiation in the olfactory bulb of adult mice. Mechanistically, FMRP and CYFIP1 modulate mTor signaling in an antagonistic manner, likely via independent pathways, supporting the results obtained in mouse as well as in fly at the morphological level. Collectively, these results illustrate a new model to explain the cellular roles of FMRP and CYFIP1 and the molecular significance of their interaction.
Song, L., He, Y., Ou, J., Zhao, Y., Li, R., Cheng, J., Lin, C.H. and Ho, M.S. (2017). Auxilin underlies progressive locomotor deficits and dopaminergic neuron loss in a Drosophila model of Parkinson's disease. Cell Rep 18: 1132-1143. PubMed ID: 28147270
Summary:
Parkinson's disease (PD) is a common neurodegenerative disorder that exhibits motor and non-motor symptoms, as well as pathological hallmarks, including dopaminergic (DA) neuron death and formation of α-synuclein (α-Syn) Lewy bodies. Cyclin-G-associated kinase (GAK), a PD susceptibility gene identified through genome-wide association studies (GWAS), is a ubiquitous serine/threonine kinase involved in clathrin uncoating, though its PD-related function remains elusive. This study implicates the Drosophila GAK homolog, auxilin (aux), in a broad spectrum of parkinsonian-like symptoms. Downregulating aux expression leads to progressive loss of climbing ability, decreased lifespan, and age-dependent DA neuron death similar to α-Syn overexpression. Reduced aux expression further enhances and accelerates α-Syn-mediated DA neuron loss. Flies with reduced aux expression are more sensitive to the toxin paraquat, suggesting that genetic and environmental factors intertwine. Taken together, these findings decipher a pivotal role for GAK/aux and suggest mechanisms underlying PD.

De Rose, F., Marotta, R., Talani, G., Catelani, T., Solari, P., Poddighe, S., Borghero, G., Marrosu, F., Sanna, E., Kasture, S., Acquas, E. and Liscia, A. (2017). Differential effects of phytotherapic preparations in the hSOD1 Drosophila melanogaster model of ALS. Sci Rep 7: 41059. PubMed ID: 28102336
Summary:
Anti-inflammatory extracts of Withania somnifera (Wse) and Mucuna pruriens (Mpe) were tested on a Drosophila model for Amyotrophic Lateral Sclerosis (ALS). In particular, the effects of Wse and Mpe were assessed following feeding the flies selectively overexpressing the wild human copper, zinc-superoxide dismutase (hSOD1-gain-of-function) in Drosophila motoneurons. Although ALS-hSOD1 mutants showed no impairment in life span, with respect to GAL4 controls, the results revealed impairment of climbing behaviour, muscle electrophysiological parameters (latency and amplitude of ePSPs) as well as thoracic ganglia mitochondrial functions. Interestingly, Wse treatment significantly increased lifespan of hSDO1 while Mpe had not effect. Conversely, both Wse and Mpe significantly rescued climbing impairment, and also latency and amplitude of ePSPs as well as failure responses to high frequency DLM stimulation. Finally, mitochondrial alterations were any more present in Wse- but not in Mpe-treated hSOD1 mutants. These results suggest that the application of Wse and Mpe might represent a valuable pharmacological strategy to counteract the progression of ALS and related symptoms.

Friday, February 17th

Bednářová, A., Hanna, M.E., Rakshit, K., O'Donnell, J.M. and Krishnan, N. (2017). Disruption of dopamine homeostasis has sexually dimorphic effects on senescence characteristics of Drosophila melanogaster. Eur J Neurosci [Epub ahead of print]. PubMed ID: 28112452
Summary:
This study investigated sexually dimorphic effects of disruptions in dopamine (DA) homeostasis and its relationship to senescence using three different Drosophila melanogaster mutants, Catsup (Catsup26) with elevated DA levels, and pale (ple2), Punch (PuZ22) with depleted DA levels. In all genotypes including controls, DA levels were significantly lower in old (45-50-day-old) flies compared with young (3-5-day-old) in both sexes. Interestingly, females have lower DA content than males at young age whereas this difference is not observed in old age, suggesting that males have a larger decline in DA levels with age. Females, in general, are longer lived compared with males in all genotypes except ple2 mutants with depleted DA levels, and females also demonstrate marked age-related decline in circadian locomotor activity compared with males. Old Catsup26 males with elevated DA levels accumulate significantly lower levels of lipid peroxidation product 4-hydroxy 2-nonenal compared with wild type, ple2 and PuZ22 mutant males. A sexually dimorphic response was also observed in the expression levels of key stress and aging associated transcription factors across genotypes with elevated or depleted DA levels. Taken together, these results reveal a novel sexually dimorphic involvement of DA in senescence characteristics of D. melanogaster.

Fletcher, M. and Kim, D.H. (2017). Age-dependent neuroendocrine signaling from sensory neurons modulates the effect of dietary restriction on longevity of Caenorhabditis elegans. PLoS Genet [Epub ahead of print]. PubMed ID: 28107363
Evolutionary Homolog Study:
Dietary restriction extends lifespan in evolutionarily diverse animals. A role for the sensory nervous system in dietary restriction has been established in Drosophila and Caenorhabditis elegans, but little is known about how neuroendocrine signals influence the effects of dietary restriction on longevity. This study shows that DAF-7/TGFβ (see Drosophila myo), which is secreted from the C. elegans amphid, promotes lifespan extension (see Drosophila lifespan and aging) in response to dietary restriction in C. elegans. DAF-7 produced by the ASI pair of sensory neurons acts on DAF-1/TGFβ (see Drosophila babo) receptors expressed on interneurons to inhibit the co-SMAD DAF-3 (see Drosophila Med). Increased activity of DAF-3 in the presence of diminished or deleted DAF-7 activity abrogates lifespan extension conferred by dietary restriction. Also, DAF-7 expression is dynamic during the lifespan of C. elegans, with a marked decrease in DAF-7 levels as animals age during adulthood. This age-dependent diminished expression contributes to the reduced sensitivity of aging animals to the effects of dietary restriction. DAF-7 signaling is a pivotal regulator of metabolism and food-dependent behavior, and these data establish a molecular link between the neuroendocrine physiology of C. elegans and the process by which dietary restriction can extend lifespan.

Banerjee, K. K., Deshpande, R. S., Koppula, P., Ayyub, C. and Kolthur-Seetharam, U. (2017). Central metabolic-sensing remotely controls nutrient -sensitive endocrine response in Drosophila via Sir2/Sirt1-upd2-IIS axis. J Exp Biol [Epub ahead of print]. PubMed ID: 28104798
Summary:
Endocrine signaling is central in coupling organismal nutrient status with maintenance of systemic metabolic homeostasis. While local nutrient sensing within the insulinogenic tissue is well-studied, distant mechanisms that relay organismal nutrient status in controlling metabolic-endocrine signaling are less understood. This study reports a novel mechanism underlying the distant regulation of metabolic endocrine response in Drosophila melanogaster. The communication between fat-body and insulin producing cells (IPCs), important for the secretion of dILPs, is regulated by the master metabolic sensor Sir2/Sirt1. This communication involves a fat body-specific direct regulation of the JAK/STAT cytokine upd2, by Sir2/Sirt1. This study also uncovered the importance of this regulation in coupling nutrient-inputs with dILP-secretion, and distantly controlling intestinal insulin signaling. These results provide fundamental mechanistic insights into the top-down control involving tissues that play key roles in metabolic sensing, endocrine signaling and nutrient uptake.
Cannon, L., Zambon, A. C., Cammarato, A., Zhang, Z., Vogler, G., Munoz, M., Taylor, E., Cartry, J., Bernstein, S. I., Melov, S. and Bodmer, R. (2017). Expression patterns of cardiac aging in Drosophila. Aging Cell 16(1): 82-92. PubMed ID: 28090760
Summary:
Aging causes cardiac dysfunction, often leading to heart failure and death. This study performed a cardiac-specific gene expression study on aging Drosophila and carried out a comparative meta-analysis with published rodent data. Pathway level transcriptome comparisons suggest that age-related, extra-cellular matrix remodeling and alterations in mitochondrial metabolism, protein handling, and contractile functions are conserved between Drosophila and rodent hearts. However, expression of only a few individual genes similarly changed over time between and even within species. Gene expression was examined in single fly hearts, and significant variability was found as has been reported in rodents. It is proposed that individuals may arrive at similar cardiac aging phenotypes via dissimilar transcriptional changes, including those in transcription factors and micro-RNAs. Finally, the data suggest the transcription factor Odd-skipped, which is essential for normal heart development, is also a crucial regulator of cardiac aging.

Thursday, February 16th

Matsunaga, T., Kohsaka, H. and Nose, A. (2017). Gap junction-mediated signaling from motor neurons regulates motor generation in the central circuits of larval Drosophila. J Neurosci [Epub ahead of print]. PubMed ID: 28115483
Summary:
This study used the peristaltic crawling of Drosophila larvae as a model to study how motor patterns are regulated by central circuits. An experimental system was constructed that allows simultaneous application of optogenetics and calcium imaging to the isolated ventral nerve cord (VNC). Next, the effects of manipulating local activity of motor neurons (MNs) on fictive locomotion were observed as waves of MN activity propagating along neuromeres. Optical inhibition of MNs with halorhodopsin3 (NpHR3) in a middle segment (A4, A5 or A6), but not other segments, dramatically decreases the frequency of the motor waves. Conversely, local activation of MNs with channelrhodopsin2 (ChR2) in a posterior segment (A6 or A7) increases the frequency of the motor waves. Since peripheral nerves mediating sensory feedback are severed in the VNC preparation, these results indicate that MNs send signals to the central circuits to regulate motor pattern generation. These results also indicate segmental specificity in the roles of MNs in motor control. The effects of the local MN activity manipulation are lost in shakB2 or ogre2, gap-junction mutations in Drosophila, or upon acute application of the gap junction blocker CBX, implicating electrical synapses in the signaling from MNs. Cell-type specific RNAi suggests shakB and ogre function in MNs and interneurons, respectively, during the signaling. These results not only reveal an unexpected role for MNs in motor pattern regulation but also introduce a powerful experimental system that enables examination of the input-output relationship among the component neurons in this system.

Lamaze, A., Öztürk-Çolak, A., Fischer, R., Peschel, N., Koh, K. and Jepson, J.E. (2017). Regulation of sleep plasticity by a thermo-sensitive circuit in Drosophila. Sci Rep 7: 40304. PubMed ID: 28084307
Summary:
Sleep is a highly conserved and essential behaviour in many species, including the fruit fly Drosophila melanogaster. In the wild, sensory signalling encoding environmental information must be integrated with sleep drive to ensure that sleep is not initiated during detrimental conditions. However, the molecular and circuit mechanisms by which sleep timing is modulated by the environment are unclear. This study introduces a novel behavioural paradigm to study this issue. It was found that in male fruit flies, onset of the daytime siesta is delayed by ambient temperatures above 29°C. This effect is termed Prolonged Morning Wakefulness (PMW). Signalling through the TrpA1 thermo-sensor is required for PMW, and TrpA1 specifically impacts siesta onset, but not night sleep onset, in response to elevated temperatures. Two critical TrpA1-expressing circuits were identified and it was shown that both contact DN1p clock neurons, the output of which is also required for PMW. Finally, the circadian blue-light photoreceptor CRYPTOCHROME was identified as a molecular regulator of PMW. The study proposes a model in which the Drosophila nervous system integrates information encoding temperature, light, and time to dynamically control when sleep is initiated. These results provide a platform to investigate how environmental inputs co-ordinately regulate sleep plasticity.

Doyle, S. E., Pahl, M. C., Siller, K. H., Ardiff, L. and Siegrist, S. E. (2017). Neuroblast niche position is controlled by PI3-kinase dependent DE-Cadherin adhesion. Development [Epub ahead of print]. PubMed ID: 28126840
Summary:
Correct positioning of stem cells within their niche is essential for tissue morphogenesis and homeostasis. Yet how stem cells acquire and maintain niche position remains largely unknown. This study shows that a subset of brain neuroblasts (NBs) in Drosophila utilize PI3-kinase and DE-cadherin to build adhesive contact for NB niche positioning. NBs remain within their native microenvironment when levels of PI3-kinase activity and DE-cadherin are elevated in NBs. This occurs through PI3-kinase dependent regulation of DE-Cadherin mediated cell adhesion between NBs and neighboring cortex glia, and between NBs and their GMC daughters. When levels of PI3-kinase activity and/or DE-Cadherin are reduced in NBs, NBs lose niche position and relocate to a non-native brain region that is rich in neurosecretory neurons, including those that secrete some of the Drosophila insulin-like peptides. Linking levels of PI3-kinase activity to strength of adhesive attachment could provide cancer stem cells and hematopoietic stem cells a means to cycle from trophic-poor to trophic-rich microenvironments.
Dubey, S.K. and Tapadia, M.G. (2017). Yorkie regulates neurodegeneration through canonical pathway and innate immune response. Mol Neurobiol [Epub ahead of print]. PubMed ID: 28102471
Summary:
Expansion of CAG repeats in certain genes has long been known to be associated with neurodegeneration, but the quest to identity the underlying mechanisms is still on. This study analyzes the role of Yorkie, the coactivator of the Hippo pathway, and provides evidence that it is a robust genetic modifier of polyglutamine (PolyQ)-mediated neurodegeneration. Yorkie reduces the pathogenicity of inclusion bodies in the cell by activating cyclin E and bantam, rather than by preventing apoptosis through DIAP1. PolyQ aggregates inhibit Yorkie functioning at the protein, rather than the transcript level, and this is probably accomplished by the interaction between PolyQ and Yorkie. PolyQ aggregates upregulate expression of antimicrobial peptides (AMPs) and Yorkie negatively regulates immune deficiency (IMD) and Toll pathways through relish and cactus, respectively, thus reducing AMPs and mitigating PolyQ affects. These studies strongly suggest a novel mechanism of suppression of PolyQ-mediated neurotoxicity by Yorkie through multiple channels.

Wednesday, February 15th

Thakur, R., Panda, A., Coessens, E., Raj, N., Yadav, S., Balakrishnan, S., Zhang, Q., Georgiev, P., Basak, B., Pasricha, R., Wakelam, M. J., Ktistakis, N. T. and Raghu, P. (2016). Phospholipase D activity couples plasma membrane endocytosis with retromer dependent recycling. Elife 5. PubMed ID: 27848911
Summary:
During illumination, the light-sensitive plasma membrane (rhabdomere) of Drosophila photoreceptors undergoes turnover with consequent changes in size and composition. However, the mechanism by which illumination is coupled to rhabdomere turnover remains unclear. Photoreceptors were found to contain a light-dependent phospholipase D (PLD) activity. During illumination, loss of PLD resulted in an enhanced reduction in rhabdomere size, accumulation of Rab7 positive, rhodopsin1-containing vesicles (RLVs) in the cell body and reduced rhodopsin protein. These phenotypes were associated with reduced levels of phosphatidic acid, the product of PLD activity and were rescued by reconstitution with catalytically active PLD. In wild-type photoreceptors, during illumination, enhanced PLD activity was sufficient to clear RLVs from the cell body by a process dependent on Arf1-GTP levels and retromer complex function. Thus, during illumination, PLD activity couples endocytosis of RLVs with their recycling to the plasma membrane thus maintaining plasma membrane size and composition.
Bruckner, J. J., Zhan, H., Gratz, S. J., Rao, M., Ukken, F., Zilberg, G. and O'Connor-Giles, K. M. (2016). Fife organizes synaptic vesicles and calcium channels for high-probability neurotransmitter release. J Cell Biol [Epub ahead of print]. PubMed ID: 27998991
Summary:
The strength of synaptic connections varies significantly and is a key determinant of communication within neural circuits. Mechanistic insight into presynaptic factors that establish and modulate neurotransmitter release properties is crucial to understanding synapse strength, circuit function, and neural plasticity. Drosophila Fife , a Piccolo-RIM homolog. has been shown to regulate neurotransmission and motor behavior through an unknown mechanism. This study demonstrates that Fife localizes and interacts with RIM (Rab3 interacting molecule) at the active zone cytomatrix to promote neurotransmitter release. Loss of Fife results in the severe disruption of active zone cytomatrix architecture and molecular organization. Through electron tomographic and electrophysiological studies, a decrease was found in the accumulation of release-ready synaptic vesicles and their release probability caused by impaired coupling to Ca2+ channels. Finally, Fife was found to be essential for the homeostatic modulation of neurotransmission. It is proposed that Fife organizes active zones to create synaptic vesicle release sites within nanometer distance of Ca2+ channel clusters for reliable and modifiable neurotransmitter release.
Oh, K.H., Haney, J.J., Wang, X., Chuang, C.F., Richmond, J.E. and Kim, H. (2017). ERG-28 controls BK channel trafficking in the ER to regulate synaptic function and alcohol response in C. elegans. Elife 6. PubMed ID: 28168949
Evolutionary Homolog Study:
Voltage- and calcium-dependent BK channels regulate calcium-dependent cellular events such as neurotransmitter release by limiting calcium influx. Their plasma membrane abundance is an important factor in determining BK current and thus regulation of calcium-dependent events. This study shows that in C. elegans, ERG-28 (see Drosophila CG17270), an endoplasmic reticulum (ER) membrane protein, promotes the trafficking of SLO-1 (see Drosophila slo) BK channels from the ER to the plasma membrane by shielding them from premature degradation. In the absence of ERG-28, SLO-1 channels undergo aspartic protease DDI-1-dependent degradation, resulting in markedly reduced expression at presynaptic terminals. Loss of erg-28 suppresses phenotypic defects of slo-1 gain-of-function mutants in locomotion, neurotransmitter release, and calcium-mediated asymmetric differentiation of the AWC olfactory neuron pair, and confer significant ethanol-resistant locomotory behavior, resembling slo-1 loss-of-function mutants, albeit to a lesser extent. These data thus indicate that the control of BK channel trafficking is a critical regulatory mechanism for synaptic transmission and neural function.

Bademosi, A. T., Lauwers, E., Padmanabhan, P., Odierna, L., Chai, Y. J., Papadopulos, A., Goodhill, G. J., Verstreken, P., van Swinderen, B. and Meunier, F. A. (2017). In vivo single-molecule imaging of syntaxin1A reveals polyphosphoinositide- and activity-dependent trapping in presynaptic nanoclusters. Nat Commun 8: 13660. PubMed ID: 28045048
Summary:
Syntaxin1A is organized in nanoclusters that are critical for the docking and priming of secretory vesicles from neurosecretory cells. Whether and how these nanoclusters are affected by neurotransmitter release in nerve terminals from a living organism is unknown. This study imaged photoconvertible syntaxin1A-mEos2 in the motor nerve terminal of Drosophila larvae by single-particle tracking photoactivation localization microscopy. Opto- and thermo-genetic neuronal stimulation increased syntaxin1A-mEos2 mobility, and reduced the size and molecular density of nanoclusters, suggesting an activity-dependent release of syntaxin1A from the confinement of nanoclusters. Syntaxin1A mobility was increased by mutating its polyphosphoinositide-binding site or preventing SNARE complex assembly via co-expression of tetanus toxin light chain. In contrast, syntaxin1A mobility was reduced by preventing SNARE complex disassembly. These data demonstrate that polyphosphoinositide favours syntaxin1A trapping, and show that SNARE complex disassembly leads to syntaxin1A dissociation from nanoclusters. Lateral diffusion and trapping of syntaxin1A in nanoclusters therefore dynamically regulate neurotransmitter release.

Tuesday, February 14th

Ng, F. S., Sengupta, S., Huang, Y., Yu, A. M., You, S., Roberts, M. A., Iyer, L. K., Yang, Y. and Jackson, F. R. (2016). TRAP-seq profiling and RNAi-based genetic screens identify conserved glial genes required for adult Drosophila behavior. Front Mol Neurosci 9: 146. PubMed ID: 28066175
Summary:
Although, glial cells have well characterized functions in the developing and mature brain, it is only in the past decade that roles for these cells in behavior and plasticity have been delineated. Glial astrocytes and glia-neuron signaling, for example, are now known to have important modulatory functions in sleep, circadian behavior, memory and plasticity. To better understand mechanisms of glia-neuron signaling in the context of behavior, cell-specific, genome-wide expression profiling was conducted of adult Drosophila astrocyte-like brain cells and RNA interference (RNAi)-based genetic screens were performed to identify glial factors that regulate behavior. Importantly, these studies demonstrate that adult fly astrocyte-like cells and mouse astrocytes have similar molecular signatures; in contrast, fly astrocytes and surface glia-different classes of glial cells-have distinct expression profiles. Glial-specific expression of 653 RNAi constructs targeting 318 genes identified multiple factors associated with altered locomotor activity, circadian rhythmicity and/or responses to mechanical stress (bang sensitivity). Of interest, one of the relevant genes encodes a vesicle recycling factor, four encode secreted proteins and three encode membrane transporters. These results strongly support the idea that glia-neuron communication is vital for adult behavior.
Sims, J.R., Ow, M.C., Nishiguchi, M.A., Kim, K., Sengupta, P. and Hall, S.E. (2016). Developmental programming modulates olfactory behavior in C. elegans via endogenous RNAi pathways. Elife 5. PubMed ID: 27351255
Evolutionary Homolog Study:
Environmental stress during early development can impact adult phenotypes via programmed changes in gene expression. C. elegans larvae respond to environmental stress by entering the stress-resistant dauer diapause pathway (see Drosophila stress response) and resume development once conditions improve (postdauers). This study shows that the osm-9 (see Drosophila iav) TRPV channel gene is a target of developmental programming and is down-regulated specifically in the ADL chemosensory neurons of postdauer adults, resulting in a corresponding altered olfactory behavior that is mediated by ADL in an OSM-9-dependent manner. A cis-acting motif bound by the DAF-3 (see Drosophila Med) SMAD and ZFP-1 (AF10) (see Drosophila Alh) proteins was found to be necessary for the differential regulation of osm-9, and both chromatin remodeling and endo-siRNA pathways were found to function as major contributors to the transcriptional silencing of the osm-9 locus. This work describes an elegant mechanism by which developmental experience influences adult phenotypes by establishing and maintaining transcriptional changes via RNAi and chromatin remodeling pathways. 

Kim, A. J., Fenk, L. M., Lyu, C. and Maimon, G. (2017). Quantitative predictions orchestrate visual signaling in Drosophila. Cell 168(1-2): 280-294.e212. PubMed ID: 28065412
Summary:
Vision influences behavior, but ongoing behavior also modulates vision in animals ranging from insects to primates. The function and biophysical mechanisms of most such modulations remain unresolved. This study combine behavioral genetics, electrophysiology, and high-speed videography to advance a function for behavioral modulations of visual processing in Drosophila. It was argued that a set of motion-sensitive visual neurons regulate gaze-stabilizing head movements. During flight turns, Drosophila perform a set of head movements that require silencing their gaze-stability reflexes along the primary rotation axis of the turn. Consistent with this behavioral requirement, pervasive motor-related inputs to the visual neurons were found, that quantitatively silence their predicted visual responses to rotations around the relevant axis while preserving sensitivity around other axes. This work proposes a function for a behavioral modulation of visual processing and illustrates how the brain can remove one sensory signal from a circuit carrying multiple related signals.
Versteven, M., Vanden Broeck, L., Geurten, B., Zwarts, L., Decraecker, L., Beelen, M., Göpfert, M.C., Heinrich, R. and Callaerts, P. (2017). Hearing regulates Drosophila aggression. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 28115690
Summary:
Aggression is a universal social behavior important for the acquisition of food, mates, territory, and social status. Aggression in Drosophila is context-dependent and can thus be expected to involve inputs from multiple sensory modalities. This study uses mechanical disruption and genetic approaches in Drosophila melanogaster to identify hearing as an important sensory modality in the context of intermale aggressive behavior. Neuronal silencing and targeted knockdown of hearing genes in the fly's auditory organ elicit abnormal aggression. Further, exposure to courtship or aggression song has opposite effects on aggression. These data define the importance of hearing in the control of Drosophila intermale aggression and open perspectives to decipher how hearing and other sensory modalities are integrated at the neural circuit level.

Monday, February 13th

Resnik-Docampo, M., Koehler, C. L., Clark, R. I., Schinaman, J. M., Sauer, V., Wong, D. M., Lewis, S., D'Alterio, C., Walker, D. W. and Jones, D. L. (2017). Tricellular junctions regulate intestinal stem cell behaviour to maintain homeostasis. Nat Cell Biol 19(1): 52-59. PubMed ID: 27992405
Summary:
Ageing results in loss of tissue homeostasis across taxa. In the intestine of Drosophila melanogaster, ageing is correlated with an increase in intestinal stem cell (ISC) proliferation, a block in terminal differentiation of progenitor cells, activation of inflammatory pathways, and increased intestinal permeability. However, causal relationships between these phenotypes remain unclear. This study demonstrates that ageing results in altered localization and expression of septate junction proteins in the posterior midgut, which is quite pronounced in differentiated enterocytes (ECs) at tricellular junctions (TCJs). Acute loss of the TCJ protein Gliotactin (Gli) in ECs results in increased ISC proliferation and a block in differentiation in intestines from young flies, demonstrating that compromised TCJ function is sufficient to alter ISC behaviour in a non-autonomous manner. Blocking the Jun N-terminal kinase signalling pathway is sufficient to suppress changes in ISC behaviour, but has no effect on loss of intestinal barrier function, as a consequence of Gli depletion. This work demonstrates a pivotal link between TCJs, stem cell behaviour, and intestinal homeostasis and provides insights into causes of age-onset and gastrointestinal diseases.
Banerjee, A. and Roy, J.K. (2017). Dicer-1 regulates proliferative potential of Drosophila larval neural stem cells through bantam miRNA based down-regulation of the G1/S inhibitor Dacapo. Dev Biol [Epub ahead of print]. PubMed ID: 28109717
Summary:
This study elucidates the role of miRNA in cell cycle regulation during brain development in Drosophila. It was found that lineage specific depletion of dicer-1, a classically acknowledged miRNA biogenesis protein in neuroblasts leads to a reduction in their numbers and size in the third instar larval central brain. These brains also show lower number of mitotically active cells and when homozygous mitotic clones were generated in an otherwise heterozygous dicer-1 mutant background via MARCM technique, they show reduced number of progeny cells in individual clones, substantiating the adverse effect of the loss of dicer-1 on the proliferative potential of neuroblasts. bantam miRNA, which has been classically reported to be involved in tissue growth was found to be expressed in neuroblasts and undergo reduced expression in Dicer-1 depleted background in the third instar larval brain. Reduction in the number and proliferative potential of neuroblasts in bantam mutant background implies a pivotal role played by bantam miRNA in maintenance of neuroblast number. Since in both Dicer-1 and bantam depleted genetic backgrounds, Dacapo, an inhibitor of cyclin E-Cdk complex, was found to have elevated expression, the study postulates a molecular mechanism involving bantam-Dacapo-Cyclin E/Cdk complex that regulates the G1-S phase transition of Drosophila neuroblasts.

Ma, X., Huang, J., Tian, Y., Chen, Y., Yang, Y., Zhang, X., Zhang, F. and Xue, L. (2017). Myc suppresses tumor invasion and cell migration by inhibiting JNK signaling. Oncogene [Epub ahead of print]. PubMed ID: 28068320
Summary:
Tumor metastasis, but not primary overgrowth, is the leading cause of mortality for cancer patients. During the past decade, Drosophila melanogaster has been well-accepted as an excellent model to address the intrinsic mechanism of different aspects of cancer progression, ranging from tumor initiation to metastasis. In a genetic screen aiming to find novel modulators of tumor invasion in Drosophila, this study identified the oncoprotein Myc as a negative regulator. While expression of Myc dramatically blocks tumor invasion and cell migration, loss of Myc promotes cell migration in vivo. The activity of Myc is further enhanced by the co-expression of its transcription partner Max. Mechanistically, Myc/Max directly upregulates the transcription of puc, which encodes an inhibitor of JNK signaling crucial for tumor invasion and cell migration. Furthermore, human cMyc potently suppresses JNK-dependent cell invasion and migration in both Drosophila and lung adenocarcinoma cell lines. These findings provide novel molecular insights into Myc-mediated cancer progression and raise the noteworthy problem in therapeutic strategies as inhibiting Myc might conversely accelerate tumor metastasis.

Resende, L.P., Truong, M.E., Gomez, A. and Jones, D.L. (2017). Intestinal stem cell ablation reveals differential requirements for survival in response to chemical challenge. Dev Biol [Epub ahead of print]. PubMed ID: 28104389
Summary:
The Drosophila intestine is maintained by multipotent intestinal stem cells (ISCs). Although increased intestinal stem cell (ISC) proliferation has been correlated with a decrease in longevity, there is some discrepancy regarding whether a decrease or block in proliferation also has negative consequences. This study identifies headcase (hdc) as a novel marker of ISCs and enteroblasts (EBs) and demonstrates that Hdc function is required to prevent ISC/EB loss through apoptosis. Hdc depletion was used as a strategy to ablate ISCs and EBs in order to test the ability of flies to survive without ISC function. While flies lacking ISCs show no major decrease in survival under unchallenged conditions, flies depleted of ISCs and EBs exhibit decreased survival rates in response to damage to mature enterocytes (EC) that line the intestinal lumen. These findings indicate that constant renewal of the intestinal epithelium is not absolutely necessary under normal laboratory conditions, but it is important in the context of widespread chemical-induced damage when significant repair is necessary.

Mohapatra, B., Zutshi, N., An, W., Goetz, B., Arya, P., Bielecki, T. A., Mustaq, I., Storck, M. D., Meza, J. L., Band, V. and Band, H. (2017). An essential role of CBL and CBL-B ubiquitin ligases in mammary stem cell maintenance. Development [Epub ahead of print]. PubMed ID: 28100467
Evolutionary Homolog Study
CBL and CBL-B ubiquitin ligases (see Drosophila Cbe) are negative regulators of tyrosine kinase signaling with established roles in the immune system. However, their physiological roles in epithelial tissues are unknown. This study used the MMTV-Cre-mediated Cbl gene deletion on a Cbl-b-null background as well as a tamoxifen-inducible mammary stem cell (MaSC)-specific Cbl/Cbl-b double knockout (DKO), using Lgr5-GFP-CreERT, to demonstrate a mammary epithelial cell-autonomous requirement of CBL and CBL-B in the maintenance of MaSCs. Using a newly engineered tamoxifen (TAM)-inducible Cbl/Cbl-b deletion model with a dual fluorescent reporter (Cblflox/flox; Cbl-bflox/flox; Rosa26-CreERT; mT/mG), it was shown that Cbl/Cbl-b DKO in mammary organoids leads to hyper-activation of AKT-mTOR signaling with depletion of MaSCs. Chemical inhibition of AKT or mTOR rescued MaSCs from Cbl/Cbl-b DKO induced depletion. These studies reveal a novel, cell-autonomous, requirement of CBL and CBL-B in epithelial stem cell maintenance during organ development and remodeling through modulation of mTOR signaling.
Bressan, R. B., Dewari, P. S., Kalantzaki, M., Gangoso, E., Matjusaitis, M., Garcia-Diaz, C., Blin, C., Grant, V., Bulstrode, H., Gogolok, S., Skarnes, W. C. and Pollard, S. M. (2017). Efficient CRISPR/Cas9-assisted gene targeting enables rapid and precise genetic manipulation of mammalian neural stem cells. Development. PubMed ID: 28096221
Evolutionary Homolog Study
Mammalian neural stem (NS) cell lines provide a tractable model for discovery across stem cell and developmental biology, regenerative medicine and neuroscience. They can be derived from foetal or adult germinal tissues and continuously propagated in vitro as adherent monolayers. NS cells are clonally expandable, genetically stable, and easily transfectable - experimental attributes compatible with targeted genetic manipulations. However, gene targeting - so critical for functional studies of embryonic stem cells - has not been exploited to date in NS cells. This study deployed CRISPR/Cas technology to demonstrate a variety of sophisticated genetic modifications via gene targeting in both mouse and human NS cell lines, including: 1) efficient targeted transgene insertion at safe harbor loci (Rosa26 and AAVS1); 2) biallelic knockout of neurodevelopmental transcription factor genes; 3) simple knockin of epitope tags and fluorescent reporters (e.g. Sox2-V5 and Sox2-mCherry); and 4) engineering of glioma mutations (TP53 deletion; H3F3A point mutations). These resources and optimized methods enable facile and scalable genome editing in mammalian NS cells, providing significant new opportunities for functional genetic analysis.

Sunday, February 12th

Jackson, B. C., Campos, J. L., Haddrill, P. R., Charlesworth, B. and Zeng, K. (2017). Variation in the intensity of selection on codon bias over time causes contrasting patterns of base composition evolution in Drosophila. Genome Biol Evol. PubMed ID: 28082609
Summary:
Four-fold degenerate coding sites form a major component of the genome, and are often used to make inferences about selection and demography, so that understanding their evolution is important. Despite previous efforts, many questions regarding the causes of base composition changes at these sites in Drosophila remain unanswered. To shed further light on this issue, a new whole-genome polymorphism dataset was obtained from D. simulans. Samples were analyzed from the putatively ancestral range of D. simulans, as well as an existing polymorphism dataset from an African population of D. melanogaster. By using D. yakuba as an outgroup, clear evidence was found for selection on 4-fold sites along both lineages over a substantial period, with the intensity of selection increasing with GC content. Based on an explicit model of base composition evolution, it is suggested that the observed AT-biased substitution pattern in both lineages is probably due to an ancestral reduction in selection intensity, and is unlikely to be the result of an increase in mutational bias towards AT alone. By using two polymorphism-based methods for estimating selection coefficients over different timescales, it was shown that the selection intensity on codon usage has been rather stable in D. simulans in the recent past, but the long-term estimates in D. melanogaster are much higher than the short-term ones, indicating a continuing decline in selection intensity, to such an extent that the short-term estimates suggest that selection is only active in the most GC-rich parts of the genome. Finally, evidence is provided for complex evolutionary patterns in the putatively neutral short introns, which cannot be explained by the standard GC-biased gene conversion model. These results reveal a dynamic picture of base composition evolution.
O'Brien, E. K., Higgie, M., Reynolds, A., Hoffmann, A. A. and Bridle, J. R. (2017). Testing for local adaptation and evolutionary potential along altitudinal gradients in rainforest Drosophila: beyond laboratory estimates. Glob Chang Biol. PubMed ID: 28070978
Summary:
Predicting how species will respond to the rapid climatic changes predicted this century is an urgent task. Species distribution models (SDMs) use the current relationship between environmental variation and species' abundances to predict the effect of future environmental change on their distributions. However, two common assumptions of SDMs are likely to be violated in many cases: (i) that the relationship of environment with abundance or fitness is constant throughout a species' range and will remain so in future and (ii) that abiotic factors (e.g. temperature, humidity) determine species' distributions. These assumptions were tested by relating field abundance of the rainforest fruit fly Drosophila birchii to ecological change across gradients that include its low and high altitudinal limits. Then, how such ecological variation affects the fitness of 35 D. birchii families transplanted in 591 cages to sites along two altitudinal gradients, was tested to determine whether genetic variation in fitness responses could facilitate future adaptation to environmental change. Overall, field abundance was highest at cooler, high-altitude sites, and declined towards warmer, low-altitude sites. By contrast, cage fitness (productivity) increased towards warmer, lower-altitude sites, suggesting that biotic interactions (absent from cages) drive ecological limits at warmer margins. In addition, the relationship between environmental variation and abundance varied significantly among gradients, indicating divergence in ecological niche across the species' range. However, there was no evidence for local adaptation within gradients, despite greater productivity of high-altitude than low-altitude populations when families were reared under laboratory conditions. Families also responded similarly to transplantation along gradients, providing no evidence for fitness trade-offs that would favour local adaptation. These findings highlight the importance of (i) measuring genetic variation in key traits under ecologically relevant conditions, and (ii) considering the effect of biotic interactions when predicting species' responses to environmental change
Graves, J. L., Jr., Hertweck, K. L., Phillips, M. A., Han, M. V., Cabral, L. G., Barter, T. T., Greer, L. F., Burke, M. K., Mueller, L. D. and Rose, M. R. (2017). Genomics of parallel experimental evolution in Drosophila. Mol Biol Evol [Epub ahead of print]. PubMed ID: 28087779
Summary:
What are the genomic foundations of adaptation in sexual populations? This question was addressed using fitness-character and whole-genome sequence data from 30 Drosophila laboratory populations. These 30 populations are part of a nearly forty-year laboratory radiation featuring three selection regimes, each shared by ten populations for up to 837 generations, with moderately large effective population sizes. Each of three sets of ten populations that shared a selection regime consist of five populations that have long been maintained under that selection regime, paired with five populations that had only recently been subjected to that selection regime. A high degree of evolutionary parallelism in fitness phenotypes was found when most-recent selection regimes are shared, as in previous studies from this laboratory. Genomic parallelism was also found with respect to the frequencies of single-nucleotide polymorphisms, transposable elements, insertions, and structural variants, which was expected. Entirely unexpected was a high degree of parallelism for linkage disequilibrium. The evolutionary genetic changes among these sexual populations are rapid and genomically extensive. This pattern may be due to segregating functional genetic variation that is abundantly maintained genome-wide by selection, variation that responds immediately to changes of selection regime.
Michalak, P., Kang, L., Sarup, P. M., Schou, M. F. and Loeschcke, V. (2017). Nucleotide diversity inflation as a genome-wide response to experimental lifespan extension in Drosophila melanogaster. BMC Genomics 18(1): 84. PubMed ID: 28088192
Summary:
Evolutionary theory predicts that antagonistically selected alleles, such as those with divergent pleiotropic effects in early and late life, may often reach intermediate population frequencies due to balancing selection, an elusive process when sought out empirically. Alternatively, genetic diversity may increase as a result of positive frequency-dependent selection and genetic purging in bottlenecked populations. While experimental evolution systems with directional phenotypic selection typically result in at least local heterozygosity loss, this study reports that selection for increased lifespan in Drosophila melanogaster leads to an extensive genome-wide increase of nucleotide diversity in the selected lines compared to replicate control lines, pronounced in regions with no or low recombination, such as chromosome 4 and centromere neighborhoods. These changes, particularly in coding sequences, are most consistent with the operation of balancing selection and the antagonistic pleiotropy theory of aging and life history traits that tend to be intercorrelated. Genes involved in antioxidant defenses, along with multiple lncRNAs, were among those most affected by balancing selection. Despite the overwhelming genetic diversification and the paucity of selective sweep regions, two genes with functions important for central nervous system and memory, Ptp10D and Ank2, evolved under positive selection in the longevity lines. Overall, the 'evolve-and-resequence' experimental approach proves successful in providing unique insights into the complex evolutionary dynamics of genomic regions responsible for longevity.
Lee, T. (2017). Wiring the Drosophila Brain with Individually Tailored Neural Lineages. Curr Biol 27(2): R77-R82. PubMed ID: 28118595
Summary:
A complex brain consists of multiple intricate neural networks assembled from distinct sets of input and output neurons as well as region-specific local interneurons. Within a given anatomical set, there exist diverse neuronal types that can vary in morphology, neural physiology, and modes of neurotransmission. The genetic programs that guide specification of neuronal types during neurogenesis preconfigure the brain. This is best demonstrated in the Drosophila central brain, which is composed of approximately 100 pairs of individually tailored neuronal lineages. Each neuronal lineage (the neurons/glia produced from a single stem cell) can contain multiple morphological classes of neurons that can consist of many analogous neuronal types. The detailed patterns of neuronal diversification are lineage-specific and can differ drastically even among neighboring neuronal lineages. Furthermore, the interrelationships between neuronal lineages and neural networks are complex. These phenomena underscore the importance of tracking all neuronal lineages in understanding brain development and evolution.
Turissini, D. A., Comeault, A. A., Liu, G., Lee, Y. C. and Matute, D. R. (2017). The ability of Drosophila hybrids to locate food declines with parental divergence. Evolution [Epub ahead of print]. PubMed ID: 28085186
Summary:
Hybrids are generally less fit than their parental species, and the mechanisms underlying their fitness reductions can manifest through different traits. For example, hybrids can have physiological, behavioral, or ecological defects, and these defects can generate reproductive isolation between their parental species. However, the rate that mechanisms of postzygotic isolation other than hybrid sterility and inviability evolve has remained largely uninvestigated, despite isolated studies showing that behavioral defects in hybrids are not only possible but might be widespread.This work studied a fundamental animal behavior - the ability of individuals to find food - and tested the rate at which it breaks down in hybrids. The ability of hybrids from 94 pairs of Drosophila species to find food was measured, and this ability was shown to decrease with increasing genetic divergence between the parental species and that male hybrids are more strongly (and negatively) affected than females. These findings quantify the rate that hybrid dysfunction evolves across the diverse radiation of Drosophila and highlights the need for future investigations of the genetic and neurological mechanisms that affect a hybrid's ability to find a suitable substrate on which to feed and breed.

Saturday, February 11th

Lopez Del Amo, V., Palomino-Schatzlein, M., Seco-Cervera, M., Garcia-Gimenez, J. L., Pallardo, F. V., Pineda-Lucena, A. and Galindo, M. I. (2017). A Drosophila model of GDAP1 function reveals the involvement of insulin signalling in the mitochondria-dependent neuromuscular degeneration. Biochim Biophys Acta 1863(3): 801-809. PubMed ID: 28065847
Summary:
Charcot-Marie-Tooth disease is a rare peripheral neuropathy for which there is no specific treatment. Some forms of Charcot-Marie-Tooth are due to mutations in the GDAP1 gene. A striking feature of mutations in GDAP1 is that they have a variable clinical manifestation, according to disease onset and progression, histology and mode of inheritance. Studies in cellular and animal models have revealed a role of GDAP1 in mitochondrial morphology and distribution, calcium homeostasis and oxidative stress. To get a better understanding of the disease mechanism, this study generated models of over-expression and RNA interference of the Drosophila Gdap1 gene. In order to get an overview about the changes that Gdap1 mutations cause in this disease model, a comprehensive determination of the metabolic profile in the flies by nuclear magnetic resonance spectroscopy was combined with gene expression analyses and biophysical tests. The results revealed that both up- and down-regulation of Gdap1 results in an early systemic inactivation of the insulin pathway before the onset of neuromuscular degeneration, followed by an accumulation of carbohydrates and an increase in the beta-oxidation of lipids. These findings are in line with emerging reports of energy metabolism impairments linked to different types of neural pathologies caused by defective mitochondrial function, which is not surprising given the central role of mitochondria in the control of energy metabolism. The relationship of mitochondrial dynamics with metabolism during neurodegeneration opens new avenues to understand the cause of the disease, and for the discovery of new biomarkers and treatments.
Lin, W. H., Giachello, C. N. and Baines, R. A. (2016). Seizure control through genetic and pharmacological manipulation of Pumilio: a key component of neuronal homeostasis. Dis Model Mech [Epub ahead of print]. PubMed ID: 28067623
Summary:
Epilepsy is a significant disorder for which approximately one-third of patients do not respond to drug treatments. Next-generation drugs, which interact with novel targets, are required to provide a better clinical outcome for these individuals. To identify potential novel targets for antiepileptic drug (AED) design, this study used RNA sequencing to identify changes in gene transcription in two seizure models of the fruitfly Drosophila melanogaster. The first model compared gene transcription between wildtype (WT) and the bangsenseless1 (parabss) mutant; a gain-of-function in the sole fly voltage-gated sodium channel (paralytic). The second model compared WT to WT fed the proconvulsant picrotoxin (PTX). 743 genes with significant altered expression levels were identified that are common to both seizure models. Of these, 339 are up-regulated and 397 are down-regulated. pumilio (pum) was down-regulated in both seizure models. Pum is a known homeostatic regulator of action potential firing in both flies and mammals. Pum achieves control of neuronal firing through binding to, and regulating translation of, the mRNA transcripts of voltage-gated sodium channels (Nav). Maintaining expression of pum in the CNS of parabss is potently anticonvulsive, whilst its reduction through RNAi-mediated knockdown is proconvulsive. Using a cell-based luciferase reporter screen, a repurposed chemical library was screened, and 12 compounds sufficient to increase activity of dPum were identified. Of these compounds, this study focused on avobenzone which significantly rescues seizure behaviour in parabss. The mode-of-action of avobenzone includes potentiation of pum expression and mirrors the ability of this homeostatic regulator to reduce the persistent voltage-gated Na+ current (INaP) in an identified neuron. This study reports a novel approach to suppress seizure and highlights the mechanisms of neuronal homeostasis as potential targets for next-generation AEDs.
Lehmann, S., Loh, S. H. and Martins, L. M. (2016). Enhancing NAD+ salvage metabolism is neuroprotective in a PINK1 model of Parkinson's disease. Biol Open. PubMed ID: 28011627
Summary:
Familial forms of Parkinson's disease (PD),. caused by mutations in PINK1 are linked to mitochondrial impairment. Defective mitochondria are also found in Drosophila models of PD with pink1 mutations. The co-enzyme nicotinamide adenine dinucleotide (NAD+) is essential for both generating energy in mitochondria and nuclear DNA repair through NAD+-consuming poly(ADP-ribose) polymerases (PARPs). This study found alterations in NAD+ salvage metabolism in Drosophila pink1 mutants and showed that a diet supplemented with the NAD+ precursor nicotinamide rescued mitochondrial defects and protected neurons from degeneration. Additionally, a mutation of Parp improved mitochondrial function and was neuroprotective in the pink1 mutants. It is concluded that enhancing the availability of NAD+ by either the use of a diet supplemented with NAD+ precursors or the inhibition of NAD+-dependent enzymes, such as PARPs, which compete with mitochondria for NAD+ is a viable approach to preventing neurotoxicity associated with mitochondrial defects.
Quan, X., Sato-Miyata, Y., Tsuda, M., Muramatsu, K., Asano, T., Takeo, S. and Aigaki, T. (2016). Deficiency of succinyl-CoA synthetase α subunit delays development, impairs locomotor activity and reduces survival under starvation in Drosophila. Biochem Biophys Res Commun [Epub ahead of print]. PubMed ID: 28017724
Summary:
Succinyl-CoA synthetase/ligase (SCS) is a mitochondrial enzyme that catalyzes the reversible process from succinyl-CoA to succinate and free coenzyme A in TCA cycle. SCS deficiencies are implicated in mitochondrial hepatoencephalomyopathy in humans. This study generated a null mutation in Scs α subunit (Scsα). The Drosophila SCS deficiency, designated ScsαKO, contained a high level of succinyl-CoA, a substrate for the enzyme, and altered levels of various metabolites in TCA cycle and glycolysis, indicating that the energy metabolism was impaired. Unlike SCSα deficiencies in humans, there was no reduction in lifespan, indicating that Scsα is not critical for viability in Drosophila. However, they showed developmental delays, locomotor activity defects, and reduced survival under starvation. It was also found that glycogen breakdown occurred during development, suggesting that the mutant flies were unable to produce sufficient energy to promote normal growth. These results suggested that SCSα is essential for proper energy metabolism in Drosophila. The ScsαKO flies should be useful as a model to understand the physiological role of SCSα as well as the pathophysiology of SCSα deficiency.

Xi, X., Lu, L., Zhuge, C. C., Chen, X., Zhai, Y., Cheng, J., Mao, H., Yang, C. C., Tan, B. C., Lee, Y. N., Chien, C. T. and Ho, M. S. (2017). The hypoparathyroidism-associated mutation in Drosophila Gcm compromises protein stability and glial cell formation. Sci Rep 7: 39856. PubMed ID: 28051179
Summary:
Differentiated neurons and glia are acquired from immature precursors via transcriptional controls exerted by factors such as proteins in the family of Glial Cells Missing (Gcm). Mammalian Gcm proteins mediate neural stem cell induction, placenta and parathyroid development, whereas Drosophila Gcm proteins act as a key switch to determine neuronal and glial cell fates and regulate hemocyte development. The present study reports a hypoparathyroidism-associated mutation R59L that alters Drosophila Gcm (Gcm) protein stability, rendering it unstable, and hyperubiquitinated via the ubiquitin-proteasome system (UPS). GcmR59L interacts with the Slimb-based SCF complex and Protein Kinase C (PKC), which possibly plays a role in its phosphorylation, hence altering ubiquitination. Additionally, R59L causes reduced Gcm protein levels in a manner independent of the PEST domain signaling protein turnover. GcmR59L proteins bind DNA, functionally activate transcription, and induce glial cells, yet at a less efficient level. Finally, overexpression of either wild-type human Gcmb (hGcmb) or hGcmb carrying the conserved hypoparathyroidism mutation only slightly affects gliogenesis, indicating differential regulatory mechanisms in human and flies. Taken together, these findings demonstrate the significance of this disease-associated mutation in controlling Gcm protein stability via UPS, hence advance our understanding on how glial formation is regulated.
Quintero-Espinosa, D., Jimenez-Del-Rio, M. and Velez-Pardo, C. (2016). Knockdown transgenic Lrrk Drosophila resists paraquat-induced locomotor impairment and neurodegeneration: A therapeutic strategy for Parkinson's disease. Brain Res. PubMed ID: 28041945
Summary:
Leucine-rich repeat kinase 2 (LRRK2) has been linked to familial and sporadic Parkinson's disease. However, it is still unresolved whether LRRK2 in dopaminergic (DAergic) neurons may or may not aggravate the phenotype. This study demonstrate that knocking down (KD) the Lrrk gene by RNAi in DAergic neurons untreated or treated with paraquat (PQ) neither affected the number of DAergic clusters, tyrosine hydroxylase (TH) protein levels, lifespan nor locomotor activity when compared to control (i.e. TH/+) flies. KD transgenic Lrrk flies dramatically increased locomotor activity in presence of TH enzyme inhibitor α-methyl-para-tyrosine (aMT), whereas no effect on lifespan was observed in both fly lines. Most importantly, KD Lrrk flies had reduced lipid peroxidation (LPO) index alone or in presence of PQ and the antioxidant minocycline (MC, 0.5 mM). Taken together, these findings suggest that Lrrk appears unessential for the viability of DAergic neurons in D. melanogaster. Moreover, Lrrk might negatively regulate homeostatic levels of dopamine, thereby dramatically increasing locomotor activity, extending lifespan, and reducing oxidative stress (OS). These data also indicate that reduced expression of Lrrk in the DAergic neurons of transgenic TH>Lrrk-RNAi/+ flies conferred PQ resistance and absence of neurodegeneration. The findings support the notion that reduced/suppressed LRRK2 expression might delay or prevent motor symptoms and/or frank Parkinsonism in individuals at risk to suffer autosomal dominant Parkinsonism (AD-P) by blocking OS-induced neurodegenerative processes in the DAergic neurons.

Friday, February 10th

Wagamitsu, S., Takase, D., Aoki, F. and Suzuki, M. G. (2017). Identification of the Doublesex protein binding sites that activate expression of lozenge in the female genital disc in Drosophila melanogaster. Mech Dev [Epub ahead of print]. PubMed ID: 28087460
Summary:
Normal sexual differentiation in the genital organs is essential for the animal species that use sexual reproduction. Although it is known that doublesex (dsx) is required for the sexual development of the genitalia in various insect species, the direct target genes responsible for the sexual differentiation of the genitalia have not been identified. The lozenge (lz) gene is expressed in the female genital disc and is essential for developments of spermathecae and accessory glands in Drosophila melanogaster. The female-specific isoform of DSX (DSXF) is required for activating lz expression in the female genital disc. However, it still remains unclear whether the DSXF directly activates the transcription of lz in the female genital disc. This study found two sequences (lz-DBS1 and lz-DBS2) within lz locus that showed high homology to the DSX binding motif identified previously. Competition assays using recombinant DSX DNA-binding domain (DSX-DBD) protein verified that the DSX-DBD protein bound to lz-DBS1 and lz-DBS2 in a sequence-specific manner with lower affinity than to the known DSX binding site in the bric-a-brac 1 (bab1) gene. Reporter gene analyses revealed that a 2.5-kbp lz genomic fragment containing lz-DBS1 and lz-DBS2 drove reporter gene (EGFP) expression in a manner similar to endogenous lz expression in the female genital disc. Mutations in lz-DBS1 alone significantly reduced the area of EGFP-expressing region, while EGFP expression in the female genital disc was abolished when both sites were mutated. These results demonstrated that DSX directly activates female-specific lz expression in the genital disc through lz-DBS1 and lz-DBS2.
Hope, C. M., Rebay, I. and Reinitz, J. (2017). DNA occupancy of polymerizing transcription factors: A chemical model of the ETS family factor Yan. Biophys J 112(1): 180-192. PubMed ID: 28076810
Summary:
Transcription factors use both protein-DNA and protein-protein interactions to assemble appropriate complexes to regulate gene expression. Although most transcription factors operate as monomers or dimers, a few, including the E26 transformation-specific family repressors Drosophila melanogaster Yan and its human homolog TEL/ETV6, can polymerize. Although polymerization is required for both the normal and oncogenic function of Yan and TEL/ETV6, the mechanisms by which it influences the recruitment, organization, and stability of transcriptional complexes remain poorly understood. Further, a quantitative description of the DNA occupancy of a polymerizing transcription factor is lacking, and such a description would have broader applications to the conceptually related area of polymerizing chromatin regulators. To expand the theoretical basis for understanding how the oligomeric state of a transcriptional regulator influences its chromatin occupancy and function, this study leveraged the extensive biochemical characterization of E26 transformation-specific factors to develop a mathematical model of Yan occupancy at chemical equilibrium. Spreading condensation from a specific binding site was found to take place in a path-independent manner given reasonable values of the free energies of specific and non-specific DNA binding and protein-protein cooperativity. The calculations show that polymerization confers upon a transcription factor the unique ability to extend occupancy across DNA regions far from specific binding sites. In contrast, dimerization promotes recruitment to clustered binding sites and maximizes discrimination between specific and non-specific sites. It is speculated that the association with non-specific DNA afforded by polymerization may enable regulatory behaviors that are well-suited to transcriptional repressors but perhaps incompatible with precise activation.
Hang, S. and Gergen, J.P. (2017). Different modes of enhancer-specific regulation by Runt and Even-skipped during Drosophila segmentation. Mol Biol Cell [Epub ahead of print]. PubMed ID: 28077616
Summary:
The initial metameric expression of the Drosophila sloppy paired 1 (slp1) gene is controlled by two distinct cis-regulatory DNA elements that interact in a non-additive manner to integrate inputs from transcription factors encoded by the pair-rule segmentation genes. This study performed Chromatin Immuno-Precipitation (ChIP) on reporter genes containing these elements in different embryonic genotypes to investigate the mechanism of their regulation. The Distal Early Stripe Element (DESE) mediates both activation and repression by Runt. The differential response of DESE to Runt was found to be due to an inhibitory effect of Fushi tarazu (Ftz) on P-TEFb recruitment and the regulation of RNA Polymerase II (Pol II) pausing. The Proximal Early Stripe Element (PESE) is also repressed by Runt, but in this case Runt prevents PESE-dependent Pol II recruitment and pre-initiation complex (PIC) assembly. PESE is also repressed by Even-skipped (Eve) but interestingly this repression involves regulation of P-TEFb recruitment and promoter-proximal Pol II pausing. These results demonstrate that the mode of slp1 repression by Runt is enhancer-specific whereas the mode of repression of the slp1 PESE enhancer is transcription factor-specific. The study proposes a model based on these differential regulatory interactions that accounts for the non-additive interactions between the PESE and DESE enhancers during Drosophila segmentation.

Yan, J., Anderson, C., Viets, K., Tran, S., Goldberg, G., Small, S. and Johnston, R. J., (2017). Regulatory logic driving stable levels of defective proventriculus expression during terminal photoreceptor specification in flies. Development [Epub ahead of print]. PubMed ID: 28126841
Summary:
How differential levels of gene expression are controlled in post-mitotic neurons is poorly understood. In the Drosophila retina, expression of the transcription factor Defective Proventriculus (Dve) at distinct cell-type-specific levels is required for terminal differentiation of color- and motion-detecting photoreceptors. This study found that the activities of two cis-regulatory enhancers are coordinated to drive dve expression in the fly eye. Three transcription factors act on these enhancers to determine cell-type-specificity. Negative autoregulation by Dve maintains expression from each enhancer at distinct homeostatic levels. One enhancer acts as an inducible backup ("dark" shadow enhancer) that is normally repressed but becomes active in the absence of the other enhancer. Thus, two enhancers integrate combinatorial transcription factor input, feedback, and redundancy to generate cell-type specific levels of dve expression and stable photoreceptor fate. This regulatory logic may represent a general paradigm for how precise levels of gene expression are established and maintained in post-mitotic neurons.

Thursday, February 9th

Lee, S., Bao, H., Ishikawa, Z., Wang, W. and Lim, H.Y. (2017). Cardiomyocyte regulation of systemic lipid metabolism by the Apolipoprotein B-containing lipoproteins in Drosophila. PLoS Genet 13: e1006555. PubMed ID: 28095410
Summary:
The heart has emerged as an important organ in the regulation of systemic lipid homeostasis; however, the underlying mechanism remains poorly understood. This study shows that Drosophila cardiomyocytes regulate systemic lipid metabolism by producing apolipoprotein B-containing lipoproteins (apoB-lipoproteins), essential lipid carriers that are so far known to be generated only in the fat body. In a Drosophila genetic screen, it was discovered that when haplo-insufficient, microsomal triglyceride transfer protein (mtp), required for the biosynthesis of apoB-lipoproteins, suppresses the development of diet-induced obesity. Tissue-specific inhibition of Mtp reveals that whereas knockdown of mtp only in the fat body decreases systemic triglyceride (TG) content on normal food diet (NFD) as expected, knockdown of mtp only in the cardiomyocytes also equally decreases systemic TG content on NFD, suggesting that the cardiomyocyte- and fat body-derived apoB-lipoproteins serve similarly important roles in regulating whole-body lipid metabolism. Unexpectedly, on high fat diet (HFD), knockdown of mtp in the cardiomyocytes, but not in fat body, protects against the gain in systemic TG levels. Inhibition of the Drosophila apoB homologue, apolipophorin or apoLpp, another gene essential for apoB-lipoprotein biosynthesis, affects systemic TG levels similarly to that of Mtp inhibition in the cardiomyocytes on NFD or HFD. Finally, HFD differentially alters Mtp and apoLpp expression in the cardiomyocytes versus the fat body, culminating in higher Mtp and apoLpp levels in the cardiomyocytes than in fat body and possibly underlying the predominant role of cardiomyocyte-derived apoB-lipoproteins in lipid metabolic regulation. These findings reveal a novel and significant function of heart-mediated apoB-lipoproteins in controlling lipid homeostasis.

Kohyama-Koganeya, A., Kurosawa, M. and Hirabayashi, Y. (2017). Loss of BOSS causes shortened lifespan with mitochondrial dysfunction in Drosophila. PLoS One 12(1): e0169073. PubMed ID: 28045997
Summary:
Aging is a universal process that causes deterioration in biological functions of an organism over its lifetime. There are many risk factors that are thought to contribute to aging rate, with disruption of metabolic homeostasis being one of the main factors that accelerates aging. Previous studies identified a new function for the putative G-protein-coupled receptor, Bride of sevenless (BOSS), in energy metabolism. Since maintaining metabolic homeostasis is a critical factor in aging, this study investigated whether BOSS plays a role in the aging process. BOSS was shown to affect lifespan regulation. boss null mutants exhibit shortened lifespans, and their locomotor performance and gut lipase activity-two age-sensitive markers-are diminished and similar to those of aged control flies. Reactive oxygen species (ROS) production is also elevated in boss null mutants, and their ROS defense system is impaired. The accumulation of protein adducts (advanced lipoxidation end products [ALEs] and advanced glycation end products [AGEs]) caused by oxidative stress are elevated in boss mutant flies. Furthermore, boss mutant flies are sensitive to oxidative stress challenges, leading to shortened lives under oxidative stress conditions. Expression of superoxide dismutase 2 (SOD2), which is located in mitochondria and normally regulates ROS removal, was decreased in boss mutant flies. Systemic overexpression of SOD2 rescued boss mutant phenotypes. Finally, mitochondrial mass was greater in boss mutant flies. These results suggest that BOSS affects lifespan by modulating the expression of a set of genes related to oxidative stress resistance and mitochondrial homeostasis.
Orsted, M., Schou, M. F. and Kristensen, T. N. (2017). Biotic and abiotic factors investigated in two Drosophila species - evidence of both negative and positive effects of interactions on performance. Sci Rep 7: 40132. PubMed ID: 28059144
Summary:
Multiple environmental factors acting in concert can interact and strongly influence population fitness and ecosystem composition. Studies investigating interactions usually involve only two environmental factors; most frequently a chemical and another abiotic factor such as a stressful temperature. This study investigated the effects of three environmental factors: temperature, an insecticide (dimethoate) and interspecific co-occurrence. Two naturally co-occurring species of Drosophila (D. hydei and D. melanogaster) were exposed to the different environments during development, and the consequences on several performance measures were examined. Results are highly species and trait specific with evidence of two- and three-way interactions in approximately 30% of all cases, suggesting that additive effects of combined environmental factors are most common, and that interactions are not universal. To provide more informative descriptions of complex interactions re-conceptualised definitions of synergism and antagonism were implemented. Approximately equal proportions of synergistic and antagonistic interactions were found in both species, however the effects of interactions on performance differed between the two. Furthermore, negative impacts on performance were found in only 60% of interactions. Thus this study also reveals a high proportion of cases with positive effects of interactions.
Somers, J., Luong, H. N., Mitchell, J., Batterham, P. and Perry, T. (2017). Pleiotropic effects of loss of the Dα1 subunit in Drosophila melanogaster: Implications for insecticide resistance. Genetics 205(1): 263-271. PubMed ID: 28049707
Summary:
Nicotinic acetylcholine receptors (nAChRs) are a highly conserved gene family that form pentameric receptors involved in fast excitatory synaptic neurotransmission. The specific roles individual nAChR subunits perform in Drosophila melanogaster and other insects are relatively uncharacterized. Of the 10 D. melanogaster nAChR subunits, only three have described roles in behavioral pathways; Dα3 and Dα4 in sleep, and Dα7 in the escape response. Other subunits have been associated with resistance to several classes of insecticides. In particular, previous work has demonstrated that an allele of the Dα1 subunit is associated with resistance to neonicotinoid insecticides. This study used ends-out gene targeting to create a knockout of the Dα1 gene to facilitate phenotypic analysis in a controlled genetic background. This is the first report of a native function for any nAChR subunits known to be targeted by insecticides. Loss of Dα1 function was associated with changes in courtship, sleep, longevity, and insecticide resistance. While acetylcholine signaling had previously been linked with mating behavior and reproduction in D. melanogaster, no specific nAChR subunit had been directly implicated. The role of Dα1 in a number of behavioral phenotypes highlights the importance of understanding the biological roles of nAChRs and points to the fitness cost that may be associated with neonicotinoid resistance.

Wednesday, February 8th

Slaidina, M. and Lehmann, R. (2017). Quantitative differences in a single maternal factor determine survival probabilities among Drosophila germ cells. Curr Biol [Epub ahead of print]. PubMed ID: 28065608
Summary:
Germ cell death occurs in many speciesand has been proposed as a mechanism by which the fittest, strongest, or least damaged germ cells are selected for transmission to the next generation. However, little is known about how the choice is made between germ cell survival and death. This study focused on the mechanisms that regulate germ cell survival during embryonic development in Drosophila. The decision to die was found to be a germ cell-intrinsic process linked to quantitative differences in germ plasm inheritance, such that higher germ plasm inheritance correlates with higher primordial germ cell (PGC) survival probability. That the maternal factor lipid phosphate phosphatase Wunen-2 (Wun2) regulates PGC survival in a dose-dependent manner. Since wun2 mRNA levels correlate with the levels of other maternal determinants at the single-cell level, it is proposed that Wun2 is used as a readout of the overall germ plasm quantity, such that only PGCs with the highest germ plasm quantity survive. Furthermore, it was demonstrated that Wun2 and p53, another regulator of PGC survival, have opposite yet independent effects on PGC survival. Since p53 regulates cell death upon DNA damage and various cellular stresses, it is hypothesized that together they ensure selection of the PGCs with highest germ plasm quantity and least cellular damage.
Khire, A., Jo, K.H., Kong, D., Akhshi, T., Blachon, S., Cekic, A.R., Hynek, S., Ha, A., Loncarek, J., Mennella, V. and Avidor-Reiss, T. (2017). Centriole remodeling during spermiogenesis in Drosophila. Curr Biol 26: 3183-3189. PubMed ID: 28094036
Summary:
The first cell of an animal (zygote) requires centrosomes that are assembled from paternally inherited centrioles and maternally inherited pericentriolar material (PCM). In some animals, sperm centrioles with typical ultrastructure are the origin of the first centrosomes in the zygote. In other animals, however, sperm centrioles lose their proteins and are thought to be degenerated and non-functional during spermiogenesis. This study shows that the two sperm centrioles (the giant centriole [GC] and the proximal centriole-like structure [PCL]) in Drosophila melanogaster are remodeled during spermiogenesis through protein enrichment and ultrastructure modification in parallel to previously described centrosomal reduction. The ultrastructure of the matured sperm (spermatozoa) centrioles is modified dramatically and the PCL does not resemble a typical centriole. Additionally, Poc1 is enriched at the atypical centrioles in the spermatozoa. Using various mutants, protein expression during spermiogenesis, and RNAi knockdown of paternal Poc1, it was found that paternal Poc1 enrichment is essential for the formation of centrioles during spermiogenesis and for the formation of centrosomes after fertilization in the zygote. Altogether, these findings demonstrate that the sperm centrioles are remodeled both in their protein composition and in ultrastructure, yet they are functional and are essential for normal embryogenesis in Drosophila.

Hayashi, M., Shinozuka, Y., Shigenobu, S., Sato, M., Sugimoto, M., Ito, S., Abe, K. and Kobayashi, S. (2017).. Conserved role of Ovo in germline development in mouse and Drosophila. Sci Rep 7: 40056. PubMed ID: 28059165
Summary:
Ovo, which encodes a transcription factor with Zn-finger domains, is evolutionarily conserved among animals. In Drosophila, in addition to its zygotic function for egg production, maternal ovo activity is required in primordial germ cells (PGCs) for expression of germline genes such as vasa and nanos. This study found that maternal Ovo accumulates in PGC nuclei during embryogenesis. In these cells, ovo serves a dual function: activation of genes expressed predominantly in PGCs, and conversely suppression of somatic genes. Reduction of ovo activity in PGCs makes them unable to develop normally into germ cells of both sexes. In mice, knockout of the ovo ortholog, Ovol2, which is expressed in PGCs, decreases the number of PGCs during early embryogenesis. These data strongly suggest that ovo acts as part of an evolutionarily conserved mechanism that regulates germline development in animals.
Helsel, A. R., Yang, Q. E., Oatley, M. J., Lord, T., Sablitzky, F. and Oatley, J. M. (2017). ID4 levels dictate the stem cell state in mouse spermatogonia. Development. PubMed ID: 28087628 Evolutionary Homolog Study

Spermatogenesis is a classic model of cycling cell lineages that depend on a balance between stem cell self-renewal for continuity and formation of progenitors as the initial step in production of differentiated cells. However, the mechanisms guiding the continuum of spermatogonial stem cell (SSC) to progenitor spermatogonial transition and precise identifiers of subtypes in the process are undefined. This study used an Id4-eGfp reporter mouse to discover that EGFP intensity is predictive of the subsets with the ID4-EGFPBright population being mostly, if not purely, SSCs while the ID4-EGFPDim population is in transition to the progenitor state. These subsets are also distinguishable by transcriptome signatures. Moreover, using a conditional overexpression mouse model, this study found that transition from the stem cell to immediate progenitor state requires down-regulation of Id4 (see Drosophila Daughterless) coincident with a major change in the transcriptome. Collectively, these results demonstrate that the level of ID4 is predictive of stem cell or progenitor capacity in spermatogonia and dictates the interface of transition between the different functional states.

Tuesday, February 7th

Yamamoto, M., Ohsawa, S., Kunimasa, K. and Igaki, T. (2017). The ligand Sas and its receptor PTP10D drive tumour-suppressive cell competition. Nature [Epub ahead of print]. PubMed ID: 28092921
Summary:
Normal epithelial cells often exert anti-tumour effects against nearby oncogenic cells. In the Drosophila imaginal epithelium, clones of oncogenic cells with loss-of-function mutations in the apico-basal polarity genes scribble or discs large are actively eliminated by cell competition when surrounded by wild-type cells. Although c-Jun N-terminal kinase (JNK) signalling plays a crucial role in this cell elimination, the initial event, which occurs at the interface between normal cells and polarity-deficient cells, has not previously been identified. Through a genetic screen in Drosophila, this study identifies the ligand Sas and the receptor-type tyrosine phosphatase PTP10D as the cell-surface ligand-receptor system that drives tumour-suppressive cell competition. At the interface between the wild-type 'winner' and the polarity-deficient 'loser' clones, winner cells relocalize Sas to the lateral cell surface, whereas loser cells relocalize PTP10D there. This leads to the trans-activation of Sas-PTP10D signalling in loser cells, which restrains EGFR signalling and thereby enables elevated JNK signalling in loser cells, triggering cell elimination. In the absence of Sas-PTP10D, elevated EGFR signalling in loser cells switches the role of JNK from pro-apoptotic to pro-proliferative by inactivating the Hippo pathway, thereby driving the overgrowth of polarity-deficient cells. These findings uncover the mechanism by which normal epithelial cells recognize oncogenic polarity-deficient neighbours to drive cell competition.

Kwan, J., et al. (2016). DLG5 connects cell polarity and Hippo signaling protein networks by linking PAR-1 with MST1/2. Genes Dev 30(24): 2696-2709. PubMed ID: 28087714
Summary:
The mechanisms connecting apical-basal polarity proteins with intracellular signaling pathways are largely unknown. This study reports that Discs large homolog 5 (DLG5) functions as an evolutionarily conserved scaffold and negative regulator of Hippo signaling, which controls organ size through the modulation of cell proliferation and differentiation. Affinity purification/mass spectrometry revealed a critical role of DLG5 in the formation of protein assemblies containing core Hippo kinases mammalian ste20 homologs 1/2 (MST1/2) and Par-1 polarity proteins microtubule affinity-regulating kinases 1/2/3 (MARK1/2/3). Consistent with this finding, Hippo signaling is markedly hyperactive in mammalian Dlg5-/- tissues and cells in vivo and ex vivo and in Drosophila upon dlg5 knockdown. Conditional deletion of Mst1/2 fully rescued the phenotypes of brain-specific Dlg5 knockout mice. Dlg5 also interacts genetically with Hippo effectors Yap1/Taz (see Drosophila Yorkie). Mechanistically, this study shows that DLG5 inhibits the association between MST1/2 and large tumor suppressor homologs 1/2 (LATS1/2; see Drosophila Warts), uses its scaffolding function to link MST1/2 with MARK3, and inhibits MST1/2 kinase activity. These data reveal a direct connection between cell polarity proteins and Hippo, which is essential for proper development of multicellular organisms.
Martins, T., Meghini, F., Florio, F. and Kimata, Y. (2017). The APC/C coordinates retinal differentiation with G1 arrest through the Nek2-dependent modulation of Wingless signaling. Dev Cell 40(1): 67-80. PubMed ID: 28041905
Summary:
The cell cycle is coordinated with differentiation during animal development. This study reports a cell-cycle-independent developmental role for a master cell-cycle regulator, the anaphase-promoting complex or cyclosome (APC/C), in the regulation of cell fate through modulation of Wingless (Wg) signaling. The APC/C controls both cell-cycle progression and postmitotic processes through ubiquitin-dependent proteolysis. Through an RNAi screen in the developing Drosophila eye, this study found that partial APC/C inactivation severely inhibits retinal differentiation independently of cell-cycle defects. The differentiation inhibition coincides with hyperactivation of Wg signaling caused by the accumulation of a Wg modulator, Drosophila Nek2 (dNek2). The APC/C degrades dNek2 upon synchronous G1 arrest prior to differentiation, which allows retinal differentiation through local suppression of Wg signaling. Evidence is provided that Decapentaplegic signaling may posttranslationally regulate this APC/C function. Thus, the APC/C coordinates cell-fate determination with the cell cycle through the modulation of developmental signaling pathways.
Blice-Baum, A.C., Zambon, A.C., Kaushik, G., Viswanathan, M.C., Engler, A.J., Bodmer, R. and Cammarato, A. (2017). Modest overexpression of FOXO maintains cardiac proteostasis and ameliorates age-associated functional decline. Aging Cell 16: 93-103. PubMed ID: 28090761
Summary:
Heart performance declines with age. Impaired protein quality control (PQC), due to reduced ubiquitin-proteasome system (UPS) activity, autophagic function, and/or chaperone-mediated protein refolding, contributes to cardiac deterioration. The transcription factor FOXO participates in regulating genes involved in PQC, senescence, and numerous other processes. In this study, a comprehensive approach, involving molecular genetics, novel assays to probe insect cardiac physiology, and bioinformatics, was utilized to investigate the influence of heart-restricted manipulation of dFOXO expression in the rapidly aging Drosophila melanogaster model. Modest dFOXO overexpression was cardioprotective, ameliorating nonpathological functional decline with age. This was accompanied by increased expression of genes associated predominantly with the UPS, relative to other PQC components, which was validated by a significant decrease in ubiquitinated proteins. RNAi knockdown of UPS candidates accordingly compromised myocardial physiology in young flies. Conversely, excessive dFOXO overexpression or suppression proved detrimental to heart function and/or organismal development. This study highlights D. melanogaster as a model of cardiac aging and FOXO as a tightly regulated mediator of proteostasis and heart performance over time.

Monday, February 6th

Sauerwald, J., Soneson, C., Robinson, M.D. and Luschnig, S. (2017). Faithful mRNA splicing depends on the Prp19 complex subunit faint sausage and is required for tracheal branching morphogenesis in Drosophila. Development [Epub ahead of print]. PubMed ID: 28087625
Summary:
Morphogenesis requires the dynamic regulation of gene expression, including transcription, mRNA maturation and translation. Dysfunction of the general mRNA splicing machinery can cause surprisingly specific cellular phenotypes, but the basis for these effects is not clear. This study shows that the Drosophila faint sausage (fas) locus, implicated in epithelial morphogenesis and previously reported to encode a secreted immunoglobulin domain protein, in fact encodes a subunit of the spliceosome-activating Prp19 complex, which is essential for efficient pre-mRNA splicing. Loss of zygotic fas function globally impairs the efficiency of splicing, and is associated with widespread retention of introns in mRNAs and dramatic changes in gene expression. Surprisingly, despite these general effects, zygotic fas mutants show specific defects in tracheal cell migration during mid-embryogenesis when maternally supplied splicing factors have declined. The study proposes that tracheal branching, which relies on dynamic changes in gene expression, is particularly sensitive for efficient spliceosome function. These results reveal an entry point to study requirements of the splicing machinery during organogenesis and provide a better understanding of disease phenotypes associated with mutations in general splicing factors.

Chen, F., Chisholm, A. D. and Jin, Y. (2017). Tissue-specific regulation of alternative polyadenylation represses expression of neuronal ankyrin isoform in C. elegans epidermal development. Development [Epub ahead of print]. PubMed ID: 28087624
Evolutionary Homolog Study
Differential mRNA polyadenylation plays an important role in shaping the neuronal transcriptome. In C. elegans, several ankyrin isoforms are produced from the unc-44 locus through alternative polyadenylation. This study identify a key role for an intronic polyadenylation site (PAS) in temporal- and tissue-specific regulation of UNC-44/ankyrin isoforms. Removing an intronic PAS results in ectopic expression of the neuronal ankyrin isoform in non-neural tissues. This mis-expression underlies epidermal developmental defects in mutants of the conserved tumor suppressor death-associated protein kinase, dapk-1. Previous studies reported that the use of this intronic PAS depends on the nuclear polyadenylation factor SYDN-1, which inhibits the RNA polymerase II CTD phosphatase SSUP-72. Consistent with this, loss of sydn-1 blocks ectopic expression of neuronal ankyrin and suppresses epidermal morphology defects of dapk-1. These effects of sydn-1 are mediated by ssup-72 autonomously in the epidermis. A peptidyl-prolyl isomerase PINN-1 antagonizes SYDN-1 in the spatiotemporal control of neuronal ankyrin isoform. Moreover, the nuclear localization of PINN-1 is altered in dapk-1 mutants. These data reveal that tissue and stage-specific expression of ankyrin isoforms relies on differential activity of positive and negative regulators of alternative polyadenylation.
Colombie, N., Choesmel-Cadamuro, V., Series, J., Emery, G., Wang, X. and Ramel, D. (2017). Non-autonomous role of Cdc42 in cell-cell communication during collective migration. Dev Biol [Epub ahead of print]. PubMed ID: 28143705
Summary:
Collective cell migration is involved in numerous processes both physiological, such as embryonic development, and pathological such as metastasis. Compared to single cell migration, collective motion requires cell behaviour coordination through an as-yet poorly understood but critical cell-cell communication mechanism. Using Drosophila border cell migration, this study shows that the small Rho GTPase Cdc42 regulates cell-cell communication. Indeed, Cdc42 controls protrusion formation in a cell non-autonomous manner. Moreover, the endocytic small GTPase Rab11 was found to control Cdc42 localisation to the periphery of migrating border cell clusters. Accordingly, over-expression of Cdc42 in border cells rescues the loss of Rab11 function. Thus, this study positions Cdc42 as a new key player in cell-cell communication, acting downstream of Rab11.
Acloque, H., Ocana, O. H., Abad, D., Stern, C. D. and Nieto, M. A. (2017). Snail2 and Zeb2 repress P-Cadherin to define embryonic territories in the chick embryo. Development. PubMed ID: 28087626
Evolutionary Homolog Study
Snail and Zeb (see Drosophila Snail and Zinc finger homeodomain 1) transcription factors induce epithelial to mesenchymal transition (EMT) in embryonic and adult tissues by direct repression of E-Cadherin (see Drosophila Shotgun) transcription. The repression of E-Cadherin transcription by the EMT inducers Snail1 and Zeb2 plays a fundamental role in defining embryonic territories in the mouse, as E-Cadherin needs to be downregulated in the primitive streak and in the epiblast concomitant with the formation of mesendodermal precursors and the neural plate, respectively. This study shows that in the chick embryo, E-Cadherin is weakly expressed in the epiblast at pre-primitive streak stages where it is substituted by P-Cadherin. Snail2 and Zeb2 were shown to repress P-Cadherin transcription in the primitive streak and the neural plate, respectively. This indicates that E- and P-Cadherin expression patterns evolved differently between chick and mouse. As such, the Snail1/E-Cadherin axis described in the early mouse embryo corresponds to Snail2/P-Cadherin in the chick, but both Snail factors and Zeb2 fulfill a similar role in chick and mouse in directly repressing ectodermal Cadherins to promote the delamination of mesendodermal precursors at gastrulation and the proper specification of the neural ectoderm during neural induction.
Chal, J., Guillot, C. and Pourquie, O. (2017). PAPC couples the segmentation clock to somite morphogenesis by regulating N-cadherin dependent adhesion. Development. PubMed ID: 28087631
Evolutionary Homolog Study
Vertebrate segmentation is characterized by the periodic formation of epithelial somites from the mesenchymal presomitic mesoderm (PSM). How the rhythmic signaling pulse delivered by the Segmentation Clock is translated into the periodic morphogenesis of somites remains poorly understood. This study focused on the role of Paraxial protocadherin (PAPC/Pcdh8) in this process. In chicken and mouse embryos, PAPC expression is tightly regulated by the Clock and Wavefront system in the posterior PSM. PAPC exhibits a striking complementary pattern to N-Cadherin (CDH2; see Drosophila Cadherin-N), marking the interface of the future somite boundary in the anterior PSM. Gain and loss of function of PAPC in chicken embryos disrupt somite segmentation by altering the CDH2-dependent epithelialization of PSM cells. These data suggest that clathrin-mediated endocytosis is increased in PAPC expressing cells, subsequently affecting CDH2 internalization in the anterior compartment of the future somite. This in turn generates a differential adhesion interface, allowing formation of the acellular fissure that defines the somite boundary. Thus periodic expression of PAPC in the anterior PSM triggers rhythmic endocytosis of CDH2, allowing for segmental de-adhesion and individualization of somites.
Sun, C., Berry, W. L. and Olson, L. E. (2017). PDGFRalpha controls the balance of stromal and adipogenic cells during adipose tissue organogenesis. Development 144(1): 83-94. PubMed ID: 28049691
Evolutionary Homolog Study
Adipose tissue is distributed in depots throughout the body with specialized roles in energy storage and thermogenesis. PDGFRα (see Drosophila PDGF- and VEGF-receptor related) is a marker of adipocyte precursors, and increased PDGFRα activity causes adipose tissue fibrosis in adult mice. However, the function of PDGFRα during adipose tissue organogenesis is unknown. By analyzing mice with juxtamembrane or kinase domain point mutations that increase PDGFRα activity (V561D or D842V), this study found that PDGFRα activation inhibits embryonic white adipose tissue organogenesis in a tissue-autonomous manner. By lineage tracing analysis, it was also found that collagen-expressing precursor fibroblasts differentiate into white adipocytes in the embryo. PDGFRα inhibited the formation of adipocytes from these precursors while favoring the formation of stromal fibroblasts. This imbalance between adipocytes and stromal cells was accompanied by overexpression of the cell fate regulator Zfp521. PDGFRα activation also inhibited the formation of juvenile beige adipocytes in the inguinal fat pad. These data highlight the importance of balancing stromal versus adipogenic cell expansion during white adipose tissue development, with PDGFRα activity coordinating this crucial process in the embryo.

Sunday, February 5th

Jindal, G. A., Goyal, Y., Yamaya, K., Futran, A. S., Kountouridis, I., Balgobin, C. A., Schupbach, T., Burdine, R. D. and Shvartsman, S. Y. (2017). In vivo severity ranking of Ras pathway mutations associated with developmental disorders. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 28049852
Summary:
Germ-line mutations in components of the Ras/MAPK pathway result in developmental disorders called RASopathies, affecting about 1/1,000 human births. Rapid advances in genome sequencing make it possible to identify multiple disease-related mutations, but there is currently no systematic framework for translating this information into patient-specific predictions of disease progression. As a first step toward addressing this issue, a quantitative, inexpensive, and rapid framework was developed that relies on the early zebrafish embryo to assess mutational effects on a common scale. Using this assay, sixteen mutations reported in MEK1 (see Drosophila Downstream of raf1), a MAPK kinase, were assessed and a robust ranking of these mutations is provided. Mutations found in cancer were found to be are more severe than those found in both RASopathies and cancer, which, in turn, are generally more severe than those found only in RASopathies. Moreover, this rank is conserved in other zebrafish embryonic assays and Drosophila-specific embryonic and adult assays, suggesting that this ranking reflects the intrinsic property of the mutant molecule. Furthermore, this rank is predictive of the drug dose needed to correct the defects. This assay can be readily used to test the strengths of existing and newly found mutations in MEK1 and other pathway components, providing the first step in the development of rational guidelines for patient-specific diagnostics and treatment of RASopathies.
Atkinson, D., Nikodinovic Glumac, J., Asselbergh, B., Ermanoska, B., Blocquel, D., Steiner, R., Estrada-Cuzcano, A., Peeters, K., Ooms, T., De Vriendt, E., Yang, X. L., Hornemann, T., Milic Rasic, V. and Jordanova, A. (2017). Sphingosine 1-phosphate lyase deficiency causes Charcot-Marie-Tooth neuropathy. Neurology [Epub ahead of print]. PubMed ID: 28077491
Summary:
This study sought to identify the unknown genetic cause in a family with an axonal form of peripheral neuropathy and atypical disease course. Both patients presented an atypical form of axonal peripheral neuropathy, characterized by acute or subacute onset and episodes of recurrent mononeuropathy. Compound heterozygous mutations were identified cosegregating with disease that were absent in controls in the SGPL1 gene, encoding sphingosine 1-phosphate lyase (SPL). The p.Ser361* mutation triggers nonsense-mediated mRNA decay. The missense p.Ile184Thr mutation causes partial protein degradation. The plasma levels of sphingosine 1-phosphate and sphingosine/sphinganine ratio were increased in the patients. Neuron-specific downregulation of the Drosophila orthologue, Sphingosine-1-phosphate lyase impaired the morphology of the neuromuscular junction and caused progressive degeneration of the chemosensory neurons innervating the wing margin bristles. It is suggested that SPL deficiency is a cause of a distinct form of Charcot-Marie-Tooth disease in humans, thus extending the currently recognized clinical and genetic spectrum of inherited peripheral neuropathies. These data emphasize the importance of sphingolipid metabolism for neuronal function.
Zhu, J.Y., Fu, Y., Nettleton, M., Richman, A. and Han, Z. (2017). High throughput in vivo functional validation of candidate congenital heart disease genes in Drosophila. Elife [Epub ahead of print]. PubMed ID: 28084990
Summary:
Genomic sequencing has implicated large numbers of genes and de novo mutations as potential disease risk factors. A high throughput in vivo model system is needed to validate gene associations with pathology. This study developed a Drosophila-based functional system to screen candidate disease genes identified from Congenital Heart Disease (CHD) patients. 134 genes were tested in the Drosophila heart using RNAi-based gene silencing. Quantitative analyses of multiple cardiac phenotypes demonstrate essential structural, functional, and developmental roles for more than 70 genes, including a subgroup encoding histone H3K4 modifying proteins. The use of Drosophila to evaluate cardiac phenotypes resulting from specific, patient-derived alleles of candidate disease genes was also demonstrated. The study, thus, describes the first high throughput in vivo validation system to screen candidate disease genes identified from patients. This approach has the potential to facilitate development of precision medicine approaches for CHD and other diseases associated with genetic factors.

Arnal, A., Jacqueline, C., Ujvari, B., Leger, L., Moreno, C., Faugere, D., Tasiemski, A., Boidin-Wichlacz, C., Misse, D., Renaud, F., Montagne, J., Casali, A., Roche, B., Mery, F. and Thomas, F. (2017). Cancer brings forward oviposition in the fly Drosophila melanogaster. Ecol Evol 7: 272-276. PubMed ID: 28070290
Summary:
Hosts often accelerate their reproductive effort in response to a parasitic infection, especially when their chances of future reproduction decrease with time from the onset of the infection. Because malignancies usually reduce survival, and hence potentially the fitness, it is expected that hosts with early cancer could have evolved to adjust their life-history traits to maximize their immediate reproductive effort. Despite the potential importance of these plastic responses, little attention has been devoted to explore how cancers influence animal reproduction. This study used an experimental setup, a colony of genetically modified Drosophila melanogaster which develop colorectal cancer in the anterior gut, to show the role of cancer in altering life-history traits. Specifically, it was tested whether females adapt their reproductive strategy in response to harboring cancer. It was found that flies with cancer reach the peak period of oviposition significantly earlier (i.e., 2 days) than healthy ones, while no difference in the length and extent of the fecundity peak was observed between the two groups of flies. Such compensatory responses to overcome the fitness-limiting effect of cancer could explain the persistence of inherited cancer-causing mutant alleles in the wild.

Saturday, February 4th

Fischer, C., Trautman, E.P., Crawford, J.M., Stabb, E.V., Handelsman, J. and Broderick, N.A. (2017). Metabolite exchange between microbiome members produces compounds that influence Drosophila behavior. Elife 6. PubMed ID: 28068220
Summary:
Animals host multi-species microbial communities (microbiomes) whose properties may result from inter-species interactions; however, current understanding of host-microbiome interactions derives mostly from studies in which elucidation of microbe-microbe interactions is difficult. In exploring how Drosophila melanogaster acquires its microbiome, this study found that a microbial community influences Drosophila olfactory behavior and egg-laying behavior differently than individual members. Drosophila prefers a Saccharomyces-Acetobacter co-culture to the same microorganisms grown individually and then mixed, a response mainly due to the conserved olfactory receptor, Or42b. Acetobacter metabolism of Saccharomyces-derived ethanol is necessary, and acetate and its metabolic derivatives are sufficient, for co-culture preference. Preference correlates with three emergent co-culture properties: ethanol catabolism, a distinct volatile profile, and yeast population decline. Egg-laying preference provides a context-dependent fitness benefit to larvae. The study describes a molecular mechanism by which a microbial community affects animal behavior and results support a model whereby emergent metabolites signal a beneficial multispecies microbiome.

Ganguly, A., Pang, L., Duong, V.K., Lee, A., Schoniger, H., Varady, E. and Dahanukar, A. (2017). A molecular and cellular context-dependent role for Ir76b in detection of amino acid taste. Cell Rep 18: 737-750. PubMed ID: 28099851
Summary:
Amino acid taste is expected to be a universal property among animals. Although sweet, bitter, salt, and water tastes have been well characterized in insects, the mechanisms underlying amino acid taste remain elusive. From a Drosophila RNAi screen, this study identified an ionotropic receptor, Ir76b, as necessary for yeast preference. Using calcium imaging, the Ir76b+ amino acid taste neurons in legs were identified and were found to be overlapping partially with sweet neurons but not those that sense other tastants. Ir76b mutants have reduced responses to amino acids, which are rescued by transgenic expression of Ir76b and a mosquito ortholog AgIr76b. Co-expression of Ir20a with Ir76b is sufficient for conferring amino acid responses in sweet-taste neurons. Notably, Ir20a also serves to block salt response of Ir76b. Overall, the study establishes the role of a highly conserved receptor in amino acid taste and suggests a mechanism for mutually exclusive roles of Ir76b in salt- and amino-acid-sensing neurons.

Arbuthnott, D., Fedina, T.Y., Pletcher, S.D. and Promislow, D.E. (2017). Mate choice in fruit flies is rational and adaptive. Nat Commun 8: 13953. PubMed ID: 28094789
Summary:
According to rational choice theory, beneficial preferences should lead individuals to sort available options into linear, transitive hierarchies, although the extent to which non-human animals behave rationally is unclear. This study demonstrates that mate choice in the fruit fly Drosophila melanogaster results in the linear sorting of a set of diverse isogenic female lines, unambiguously demonstrating the hallmark of rational behaviour, transitivity. These rational choices are associated with direct benefits, enabling males to maximize offspring production. Furthermore, female behaviours and cues act redundantly in mate detection and assessment, as rational mate choice largely persists when visual or chemical sensory modalities are impaired, but not when both are impaired. Transitivity in mate choice demonstrates that the quality of potential mates varies significantly among genotypes, and that males and females behave in such a way as to facilitate adaptive mate choice.

Hilbert, Z.A. and Kim, D.H. (2017). Sexually dimorphic control of gene expression in sensory neurons regulates decision-making behavior in C. elegans. Elife 6. PubMed ID: 28117661
Evolutionary Homolog Study:
Animal behavior is directed by the integration of sensory information from internal states and the environment. Neuroendocrine regulation of diverse behaviors of Caenorhabditis elegans is under the control of the DAF-7/TGF-β (see Drosophila myo) ligand that is secreted from sensory neurons. This study shows that C. elegans males exhibit an altered, male-specific expression pattern (see Drosophila sex determination) of daf-7 in the ASJ sensory neuron pair with the onset of reproductive maturity, which functions to promote male-specific mate-searching behavior. Molecular genetic analysis of the switch-like regulation of daf-7 expression in the ASJ neuron pair reveals a hierarchy of regulation among multiple inputs-sex, age, nutritional status, and microbial environment-which function in the modulation of behavior. These results suggest that regulation of gene expression in sensory neurons can function in the integration of a wide array of sensory information and facilitate decision-making behaviors in C. elegans.

Yilmazer, Y. B., Koganezawa, M., Sato, K., Xu, J. and Yamamoto, D. (2016). Serotonergic neuronal death and concomitant serotonin deficiency curb copulation ability of Drosophila platonic mutants. Nat Commun 7: 13792. PubMed ID: 27958269
Summary:
Drosophila platonic (plt) males court females, but fail to copulate. This study shows that plt is an allele of scribbler (sbb), a BMP signalling component. sbb knockdown in larvae leads to the loss of approximately eight serotonergic neurons, which express the sex-determinant protein Doublesex (Dsx). Genetic deprivation of serotonin (5-HT) from dsx-expressing neurons results in copulation defects. Thus, sbb+ is developmentally required for the survival of a specific subset of dsx-expressing neurons, which support the normal execution of copulation in adults by providing 5-HT. This study highlights the conserved involvement of serotonergic neurons in the control of copulatory mechanisms and the key role of BMP signalling in the formation of a sex-specific circuitry.
Houot, B., Gigot, V., Robichon, A. and Ferveur, J. F. (2017). Free flight odor tracking in Drosophila: Effect of wing chemosensors, sex and pheromonal gene regulation. Sci Rep 7: 40221. PubMed ID: 28067325
Summary:
The evolution of powered flight in insects had major consequences for global biodiversity and involved the acquisition of adaptive processes allowing individuals to disperse to new ecological niches. Flies use both vision and olfactory input from their antennae to guide their flight; chemosensors on fly wings have been described, but their function remains mysterious. This study examineed Drosophila flight in a wind tunnel. By genetically manipulating wing chemosensors, it was shown that these structures play an essential role in flight performance with a sex-specific effect. Pheromonal systems are also involved in Drosophila flight guidance: transgenic expression of the pheromone production and detection gene, desat1, produced low, rapid flight that was absent in control flies. This study suggests that the sex-specific modulation of free-flight odor tracking depends on gene expression in various fly tissues including wings and pheromonal-related tissues.

Friday, February 3rd

Groen, S. C., LaPlante, E. R., Alexandre, N. M., Agrawal, A. A., Dobler, S. and Whiteman, N. K. (2016). Multidrug transporters and organic anion transporting polypeptides protect insects against the toxic effects of cardenolides. Insect Biochem Mol Biol 81: 51-61. PubMed ID: 28011348
Summary:
In the struggle against dietary toxins, insects are known to employ target site insensitivity, metabolic detoxification, and transporters that shunt away toxins. Specialized insects across six taxonomic orders feeding on cardenolide-containing plants have convergently evolved target site insensitivity via specific amino acid substitutions in the Na/K-ATPase. Nonetheless, in vitro pharmacological experiments have suggested a role for multidrug transporters (Mdrs; see mdr49 and mdr65) and organic anion transporting polypeptides (Oatps), which may provide a basal level of protection in both specialized and non-adapted insects. This study used wildtype and mutant Drosophila quantify toxicity of three chemically diverse, medically relevant cardenolides. While the three cardenolides each stimulated feeding (i.e., no deterrence to the toxin), all decreased lifespan, with the most apolar cardenolide having the lowest LD50 value. Flies showed a clear non-monotonic dose response and experienced high levels of toxicity at the cardenolide concentration found in plants. At this concentration, both Mdr and Oatp knockout mutant flies died more rapidly than wildtype flies, and the mutants also experienced more adverse neurological effects on high-cardenolide-level diets. This study further establishes Drosophila as a model for the study of cardenolide pharmacology and solidifies support for the hypothesis that multidrug and organic anion transporters are key players in insect protection against dietary cardenolides.
Misra, T., Baccino-Calace, M., Meyenhofer, F., Rodriguez-Crespo, D., Akarsu, H., Armenta-Calderon, R., Gorr, T. A., Frei, C., Cantera, R., Egger, B. and Luschnig, S. (2016). A genetically encoded biosensor for visualizing hypoxia responses in vivo. Biol Open. PubMed ID: 28011628
Summary:
.Cells experience different oxygen concentrations depending on location, organismal developmental stage, and physiological or pathological conditions. Responses to reduced oxygen levels (hypoxia) rely on the conserved Hypoxia-Inducible Factor 1 (HIF-1). Understanding the developmental and tissue-specific responses to changing oxygen levels has been limited by the lack of adequate tools for monitoring HIF-1 in vivo. To visualise and analyse HIF-1 dynamics in Drosophila, this study used a hypoxia biosensor consisting of GFP fused to the oxygen-dependent degradation domain (ODD) of the HIF-1 homologue Sima. GFP-ODD responds to changing oxygen levels and to genetic manipulations of the hypoxia pathway, reflecting oxygen-dependent regulation of HIF-1 at the single-cell level. Ratiometric imaging of GFP-ODD and a red-fluorescent reference protein reveals tissue-specific differences in the cellular hypoxic status at ambient normoxia. Strikingly, cells in the larval brain show distinct hypoxic states that correlate with the distribution and relative densities of respiratory tubes. A set of genetic and image analysis tools is presented that enable new approaches to map hypoxic microenvironments, to probe effects of perturbations on hypoxic signalling, and to identify new regulators of the hypoxia response.
Bowman, E. and Tatar, M. (2016). Reproduction regulates Drosophila nutrient intake through independent effects of egg production and sex peptide: Implications for aging. Nutr Healthy Aging 4(1): 55-61. PubMed ID: 28035342
Summary:
The ratio of protein to carbohydrate (P:C) consumed influences reproduction and lifespan, outcomes that are often maximized by different P:C intake. The purposed of this study was to determine if reproduction in female Drosophila drives elevated P:C intake and distinguish whether such a preference is driven by egg production or from male-derived sex peptides in seminal fluid. Intake of protein and carbohydrate was measured in a diet-choice assay. Macronutrient intake was calculated for mated and unmated fertile females, mated and unmated sterile females, and both types of female when mated to wildtype males and to males lacking sex peptide. Mated females were found to have high P:C intake relative to unmated females and mated, sterile females. Fertile females mated to wildtype males and to males lacking sex peptide have high P:C intake, but sterile females have similar, low P:C intake when unmated and when mated to males lacking sex peptide.It is concluded that the metabolic demands of egg production and sex peptides are individually sufficient to drive elevated P:C intake in adult female Drosophila. Reproductive state can thus modulate how animals consume macronutrients, which in turn can impact their health and aging.
Dobson, A.J., Ezcurra, M., Flanagan, C.E., Summerfield, A.C., Piper, M.D., Gems, D. and Alic, N. (2017). Nutritional programming of lifespan by FOXO inhibition on sugar-rich diets. Cell Rep 18: 299-306. PubMed ID: 28076775
Summary:
Consumption of unhealthy diets is exacerbating the burden of age-related ill health in aging populations. Such diets can program mammalian physiology to cause long-term, detrimental effects. This study shows that in Drosophila melanogaster, an unhealthy, high-sugar diet in early adulthood programs lifespan to curtail later-life survival despite subsequent dietary improvement. Excess dietary sugar promotes insulin-like signaling, inhibits dFOXO-the Drosophila homolog of forkhead box O (FOXO) transcription factors-and represses expression of dFOXO target genes encoding epigenetic regulators. Crucially, dfoxo is required both for transcriptional changes that mark the fly's dietary history and for nutritional programming of lifespan by excess dietary sugar, and this mechanism is conserved in Caenorhabditis elegans. The study implicates FOXO factors, the evolutionarily conserved determinants of animal longevity, in the mechanisms of nutritional programming of animal lifespan.

Thursday, February 2nd

Takács, Z., Jankovics, F., Vilmos, P., Lénárt, P., Röper, K. and Erdélyi, M. (2017). The spectraplakin short stop is an essential microtubule regulator involved in epithelial closure in Drosophila. J Cell Sci [Epub ahead of print]. PubMed ID: 28062848
Summary:
Dorsal closure of the Drosophila embryonic epithelium provides an excellent model system for the in vivo analysis of molecular mechanisms regulating cytoskeletal rearrangements. This study investigated the function of the Drosophila spectraplakin Short stop (Shot), a conserved cytoskeletal structural protein, during closure of the dorsal embryonic epithelium. It was found that Shot is essential for the efficient final zippering of the opposing epithelial margins. Using isoform-specific mutant alleles and genetic rescue experiments with truncated Shot variants, it was demonstrated that Shot functions as an actin-microtubule cross-linker in mediating zippering. At the leading edge of epithelial cells, Shot regulates protrusion dynamics by promoting filopodia formation. FRAP analysis and in vivo imaging of microtubule growth reveal that Shot stabilizes dynamic microtubules. The actin- and microtubule- binding activities of Shot are simultaneously required in the same molecule indicating that Shot is engaged as a physical crosslinker in this process. The study proposes that Shot-mediated interactions between microtubules and actin filaments facilitate filopodia formation which promotes zippering by initiating contacting of opposing epithelial cells.

Krieg, M., Stühmer, J., Cueva, J.G., Fetter, R., Spliker, K.A., Cremers, D., Shen, K., Dunn, A.R. and Goodman, M.B. (2017). Genetic defects in β-spectrin and tau sensitize C. elegans axons to movement-induced damage via torque-tension coupling. Elife [Epub ahead of print]. PubMed ID: 28098556
Evolutionary Homolog Study:
Our bodies are in constant motion and so are the neurons that invade each tissue. Motion-induced neuron deformation and damage are associated with several neurodegenerative conditions. This study investigated the question of how the neuronal cytoskeleton protects axons and dendrites from mechanical stress, exploiting mutations in UNC-70 β-spectrin (see Drosophila β-spectrin), PTL-1 tau/MAP2-like (see Drosophila tau) and MEC-7 β-tubulin (see Drosophila βTub56D) proteins in Caenorhabditis elegans. It was found that mechanical stress induces supercoils and plectonemes in the sensory axons of spectrin and tau double mutants. Biophysical measurements, super-resolution and electron microscopy, as well as numerical simulations of neurons as discrete, elastic rods provide evidence that a balance of torque, tension, and elasticity stabilizes neurons against mechanical deformation. The study concludes that the spectrin and microtubule cytoskeletons (see Drosophila cytoskeleton) work in combination to protect axons and dendrites from mechanical stress, and proposes that defects in β-spectrin and tau may sensitize neurons to damage.

Vasquez, C. G., Heissler, S. M., Billington, N., Sellers, J. R. and Martin, A. C. (2016). Drosophila non-muscle myosin II motor activity determines the rate of tissue folding. Elife 5 [Epub ahead of print]. PubMed ID: 28035903
Summary:
Non-muscle cell contractility is critical for tissues to adopt shape changes. Although, the non-muscle myosin II holoenzyme (myosin) is a molecular motor that powers contraction of actin cytoskeleton networks, recent studies have questioned the importance of myosin motor activity cell and tissue shape changes. Combining the biochemical analysis of enzymatic and motile properties for purified myosin mutants with in vivo measurements of apical constriction for the same mutants, this study shows that in vivo constriction rate scales with myosin motor activity. This study shows that recombinant Drosophila myosin is regulated in an on/off manner by regulatory light chain (RLC) phosphorylation. Phosphorylation of the RLC at Threonine-20 or Serine-21 activates myosin motor activity in addition to promoting the formation of bipolar filaments composed of 12.8 myosins under physiological conditions in vitro. RLC phosphorylation at Threonine-20 results in different mechanoenzymatic properties than phosphorylation at Serine-21, in agreement with Serine-21 being the primary phosphorylation site. The similarity in regulatory properties between Drosophila myosin and vertebrate myosins qualifies Drosophila as an excellent model organism to study the underlying principles of myosin function and regulation in complex processes such as cell contraction and tissue folding. So-called phosphomimetic mutants of the Drosophila RLC do not mimic the phosphorylated RLC state in vitro. The defect in the myosin motor activity in these mutants is evident in developing Drosophila embryos where tissue recoil following laser ablation is decreased compared to wild-type tissue. Overall, these data highlights that myosin activity is required for rapid cell contraction and tissue folding in developing Drosophila embryos.
Padmanabhan, A., Ong, H. T. and Zaidel-Bar, R. (2016). Non-junctional E-Cadherin clusters regulate the actomyosin cortex in the C. elegans zygote. Curr Biol [Epub ahead of print]. PubMed ID: 27989674
Evolutionary Homolog Study
Classical cadherins (see Drosophila Shotgun) are well known for their essential function in mediating cell-cell adhesion via their extra-cellular cadherin domains and intra-cellular connections to the actin cytoskeleton. There is evidence, however, of adhesion-independent cadherin clusters existing outside of cell-cell junctions. What function, if any, these clusters have is not known. HMR-1, the sole classical cadherin in Caenorhabditis elegans, plays essential roles during gastrulation, blastomere polarity establishment, and epidermal morphogenesis. To elucidate the physiological roles of non-junctional cadherin, HMR-1 was analyzed in the C. elegans zygote, which is devoid of neighbors. Non-junctional clusters of HMR-1 form during the one-cell polarization stage and associate with F-actin at the cortex during episodes of cortical flow. Non-junctional HMR-1 clusters downregulate RHO-1 (see Drosophila Rho1) activity and inhibit accumulation of non-muscle myosin II (NMY-2; see Drosophila Zipper ) at the anterior cortex. HMR-1 clusters were found to impede cortical flows and play a role in preserving the integrity of the actomyosin cortex, preventing it from splitting in two. Importantly, an inverse relationship was uncovered between the amount of HMR-1 at the cell surface and the rate of cytokinesis. The effect of HMR-1 clusters on cytokinesis is independent of their effect on NMY-2 levels, and is also independent of their extra-cellular domains. Thus, in addition to their canonical role in inter-cellular adhesion, HMR-1 clusters regulate RHO-1 activity and NMY-2 level at the cell surface, reinforce the stability of the actomyosin cortex, and resist its movement to influence cell-shape dynamics.

Wednesday, February 1st

Robertson, S. M., Medina, J., Oldenbroek, M. and Lin, R. (2017). Reciprocal signaling by Wnt and Notch specifies a muscle precursor in the C. elegans embryo. Development [Epub ahead of print]. PubMed ID: 28049659
Evolutionary Homolog Study
The MS blastomere produces one third of the body-wall muscles (BWMs) in the C. elegans embryo. MS-derived BWMs require two distinct cell-cell interactions, the first inhibitory and the second, two cell cycles later, required to overcome this inhibition. The inductive interaction is not required if the inhibitory signal is absent. Although the Notch receptor GLP-1 (see Drosophila Notch) was implicated in both interactions, the molecular nature of the two signals was unknown. This study now shows that zygotically-expressed MOM-2 (Wnt; see Drosophila Wingless) is responsible for both interactions. Both the inhibiting and the activating interactions require precise spatiotemporal expression of zygotic MOM-2, which is dependent upon two distinct Notch signals. In a Notch mutant defective only in the inductive interaction, MS-derived BWMs can be restored by preventing zygotic MOM-2 expression, which removes the inhibitory signal. These results suggest that the inhibitory interaction ensures the differential lineage specification of MS and its sister blastomere, whereas the inductive interaction promotes the expression of muscle-specifying genes by modulating TCF (see Drosophila Pangolin) and β-catenin (see Drosophila Armadillo) levels. These results highlight the complexity of cell fate specification by cell-cell interactions in a rapidly dividing embryo.
Gerdoe-Kristensen, S., Lund, V. K., Wandall, H. H. and Kjaerulff, O. (2016). Mactosylceramide prevents glial cell overgrowth by inhibiting insulin and fibroblast growth factor receptor signaling. J Cell Physiol [Epub ahead of print]. PubMed ID: 28019653
Summary:
By affecting clustering and activity of membrane receptors, Glycosphingolipids (GSL) modulate signal transduction, including that mediated by the RTK. Drosophila has a simple GSL biosynthetic pathway, in which the mannosyltransferase Egghead controls conversion of glucosylceramide (GlcCer) to mactosylceramide (MacCer). Lack of elongated GSL in egghead (egh) mutants causes overgrowth of subperineurial glia (SPG), largely due to aberrant activation of phosphatidylinositol 3-kinase (PI3K). However, to what extent this effect involves changes in upstream signaling events is unresolved. This study shows that glial overgrowth in egh is strongly linked to increased activation of Insulin receptor and Fibroblast Growth Factor receptor (FGFR). Glial hypertrophy is phenocopied when overexpressing gain-of-function mutants of the Drosophila Insulin Receptor (InR) and the FGFR homolog Heartless (Htl) in wild type SPG, and is suppressed by inhibiting Htl and InR activity in egh. Knockdown of GlcCer synthase in the SPG fails to suppress glial overgrowth in egh nerves, and slightly promotes overgrowth in wild type, suggesting that RTK hyperactivation is caused by absence of MacCer and not by GlcCer accumulation. It is concluded that an early product in GSL biosynthesis, MacCer, prevents inappropriate activation of Insulin and Fibroblast Growth Factor Receptors in Drosophila glia.
Kannan, R., Song, J.K., Karpova, T., Clarke, A., Shivalkar, M., Wang, B., Kotlyanskaya, L., Kuzina, I., Gu, Q. and Giniger, E. (2017). The Abl pathway bifurcates to balance Enabled and Rac signaling in axon patterning in Drosophila. Development [Epub ahead of print]. PubMed ID: 28087633
Summary:
The Abl tyrosine kinase signaling network controls cell migration, epithelial organization, axon patterning and other aspects of development. While individual components are known, the relationships among them remain mysterious. This study used FRET measurements of pathway activity, analysis of protein localization and genetic epistasis to dissect the structure of this network in Drosophila. It was found that the adaptor protein Disabled stimulates Abl kinase activity. Abl suppresses the actin regulatory factor Enabled, and Abl also acts through the GEF Trio to stimulate the signaling activity of Rac GTPase: Abl gates the activity of the spectrin repeats of Trio, allowing them to relieve intramolecular repression of Trio GEF activity by the Trio N-terminal domain. Finally, a key target of Abl signaling in axons is the WAVE complex that promotes formation of branched actin networks. Thus, Abl constitutes a bifurcating network, suppressing Ena activity in parallel with stimulation of WAVE. The study suggests that the balancing of linear and branched actin networks by Abl is likely to be central to its regulation of axon patterning.

Yoon, W. H., Sandoval, H., Nagarkar-Jaiswal, S., Jaiswal, M., Yamamoto, S., Haelterman, N. A., Putluri, N., Putluri, V., Sreekumar, A., Tos, T., Aksoy, A., Donti, T., Graham, B. H., Ohno, M., Nishi, E., Hunter, J., Muzny, D. M., Carmichael, J., Shen, J., Arboleda, V. A., Nelson, S. F., Wangler, M. F., Karaca, E., Lupski, J. R. and Bellen, H. J. (2016). Loss of Nardilysin, a mitochondrial co-chaperone for alpha-Ketoglutarate dehydrogenase, promotes mTORC1 activation and neurodegeneration. Neuron [Epub ahead of print]. PubMed ID: 28017472
Summary:
Mutations in Nardilysin (dNrd1) were identified in a forward genetic screen designed to isolate genes whose loss causes neurodegeneration in Drosophila photoreceptor neurons. NRD1 is localized to mitochondria, where it recruits mitochondrial chaperones and assists in the folding of alpha-ketoglutarate dehydrogenase (OGDH), a rate-limiting enzyme in the Krebs cycle. Loss of Nrd1 or Ogdh leads to an increase in alpha-ketoglutarate, a substrate for OGDH, which in turn leads to mTORC1 activation and a subsequent reduction in autophagy. Inhibition of mTOR activity by rapamycin or partially restoring autophagy delays neurodegeneration in dNrd1 mutant flies. In summary, this study reveals a novel role for NRD1 as a mitochondrial co-chaperone for OGDH and provides a mechanistic link between mitochondrial metabolic dysfunction, mTORC1 signaling, and impaired autophagy in neurodegeneration.

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