The Interactive Fly, Drosophila
What's new in edition 68 |
Gene sites new with this edition
The Interactive Fly was first released July/August 1996, with updates provided at approximately one month intervals, through September 1997 (edition 13). Updating quarterly started with edition 14. With edition 40, the Interactive Fly began to schedule updates three times a year: fall, winter and spring.
- Gene sites new with this edition of the Interactive Fly:
- α Catenin
The linkage of adherens junctions to the actin cytoskeleton is essential for cell adhesion. The contribution of the cadherin-catenin complex to the interaction between actin and the adherens junction remains an intensely investigated subject that centres on the function of α-catenin, which binds to cadherin through β-catenin and can bind F-actin directly or indirectly. This study delineates regions within Drosophila α-Catenin (α-Cat) that are important for adherens junction performance in static epithelia and dynamic morphogenetic processes. Moreover, whether persistent α-catenin-mediated physical linkage between cadherin and F-actin is crucial for cell adhesion is addressed, and the functions of α-catenin monomers and dimers at adherens junctions is characterized. The data support the view that monomeric α-catenin acts as an essential physical linker between the cadherin-β-catenin complex and the actin cytoskeleton, whereas α-catenin dimers are cytoplasmic and form an equilibrium with monomeric junctional α-catenin (Desai, 2013).
SUMOylation is a highly conserved post-translational modification shown to modulate target protein activity in a wide variety of cellular processes. Although the requirement for SUMO modification (see Drosophila Smt3) of specific substrates has received significant attention in vivo and in vitro, the developmental requirements for SUMOylation at the cell and tissue level remain poorly understood. This study shows that in Drosophila melanogaster, both heterodimeric components of the SUMO E1-activating enzyme are zygotically required for mitotic progression but are dispensable for cell viability, homeostasis and DNA synthesis in non-dividing cells. Explaining the lack of more pleiotropic effects following a global block of SUMO conjugation, it was further demonstrated that low levels of global substrate SUMOylation are detected in mutants lacking either or both E1 subunits. These results not only suggest that minimal SUMOylation persists in the absence of the E1 SUMO-activating complex comprising the Aos1/Uba2 heterodimeric pair (see Schematic representation of the SUMOylation pathway), but also show that the process of cell division is selectively sensitive to reductions in global SUMOylation. Supporting this view, knockdown of SUMO or its E1 and E2 enzymes robustly disrupts proliferating cells in the developing eye, without any detectable effects on the development or differentiation of neighboring post-mitotic cells (Kanakousaki, 2012).
- Brain-specific homeobox
The Drosophila optic lobe comprises a wide variety of neurons forming laminar and columnar structures similar to the mammalian brain. The Drosophila optic lobe may provide an excellent model to investigate various processes of brain development. However, it is poorly understood how neuronal specification is regulated in the optic lobe to form a complicated structure. This study shows that the Brain-specific-homeobox (Bsh) protein, which is expressed in the lamina and medulla ganglia, is involved in specifying neuronal identity. Bsh is expressed in L4 and L5 lamina neurons and in Mi1 medulla neurons. Analyses of loss-of-function and gain-of-function clones suggest that Bsh is required and largely sufficient for Mi1 specification in the medulla and L4 specification in the lamina. Additionally, Bsh is at least required for L5 specification. In the absence of Bsh, L5 is transformed into glial cells (Hasegawa, 2013).
Cbl-associated protein (CAP) localizes to focal adhesions and associates with numerous cytoskeletal proteins; however, its physiological roles remain unknown. This study demonstrates that Drosophila CAP regulates the organization of two actin-rich structures in Drosophila: muscle attachment sites (MASs), which connect somatic muscles to the body wall; and scolopale cells, which form an integral component of the fly chordotonal organs and mediate mechanosensation. Drosophila CAP mutants exhibit aberrant junctional invaginations and perturbation of the cytoskeletal organization at the MAS. CAP depletion also results in collapse of scolopale cells within chordotonal organs, leading to deficits in larval vibration sensation and adult hearing. This study investigated the roles of different CAP protein domains in its recruitment to, and function at, various muscle subcellular compartments. Depletion of the CAP-interacting protein Vinculin results in a marked reduction in CAP levels at MASs, and vinculin mutants partially phenocopy Drosophila CAP mutants. These results show that CAP regulates junctional membrane and cytoskeletal organization at the membrane-cytoskeletal interface of stretch-sensitive structures, and they implicate integrin signaling through a CAP/Vinculin protein complex in stretch-sensitive organ assembly and function (Bharadwaj, 2013).
- CCK-like receptor at 17D1
Neuropeptide signaling is integral to many aspects of neural communication, particularly modulation of membrane excitability and synaptic transmission. However, neuropeptides have not been clearly implicated in synaptic growth and development. This study demonstrates that cholecystokinin-like receptor (CCKLR), and Drosulfakinin (DSK), its predicted ligand, are strong positive growth regulators of the Drosophila melanogaster larval neuromuscular junction (NMJ). Mutations of CCKLR (CCKLR-17D1 but not CCKLR-17D3) or dsk produce severe NMJ undergrowth, whereas overexpression of CCKLR causes overgrowth. Presynaptic expression of CCKLR is necessary and sufficient for regulating NMJ growth. CCKLR and dsk mutants also reduce synaptic function in parallel with decreased NMJ size. Analysis of double mutants revealed that DSK/CCKLR regulation of NMJ growth occurs through the cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA)-cAMP response element binding protein (CREB) pathway. These results demonstrate a novel role for neuropeptide signaling in synaptic development. Moreover, because the cAMP-PKA-CREB pathway is required for structural synaptic plasticity in learning and memory, DSK/CCKLR signaling may also contribute to these mechanisms (Chen, 2012).
During interphase in Drosophila neuroblasts, the Centrobin (Cnb)-positive daughter centriole retains pericentriolar material (PCM) and organizes an aster that is a key determinant of the orientation of cell division. This study shows that daughter centrioles depleted of CNB cannot fulfill this function whereas mother centrioles that carry ectopic CNB can. CNB co-precipitates with a set of centrosomal proteins that include gamma-Tub, Ana2, Cnn, Sas-4, Asl, DGRIP71, Polo and Sas-6. Following chemical inhibition of Polo or removal of three Polo phosphorylation sites present in Cnb, the interphase microtubule aster is lost. These results demonstrate that centriolar Cnb localization is both necessary and sufficient to enable centrioles to retain PCM and organize the interphase aster in Drosophila neuroblasts. They also reveal an interphase function for Polo in this process that seems to have co-opted part of the protein network involved in mitotic centrosome maturation (Januschke, 2013).
The chromosomal passenger complex (CPC), containing Aurora B kinase, Inner Centromere Protein, Survivin, and Borealin, regulates chromosome condensation and interaction between kinetochores and microtubules at metaphase, then relocalizes to midzone microtubules at anaphase and regulates central spindle organization and cytokinesis. However, the precise role(s) played by the CPC in anaphase have been obscured by its prior functions in metaphase. This study identified a missense allele of Drosophila Survivin (FlyBase name: Deterin) that allows CPC localization and function during metaphase but not cytokinesis. Analysis of mutant cells showed that Survivin is essential to target the CPC and the mitotic kinesin-like protein 1 orthologue Pavarotti (Pav) to the central spindle and equatorial cell cortex during anaphase in both larval neuroblasts and spermatocytes. Survivin also enabled localization of Polo kinase and Rho at the equatorial cortex in spermatocytes, critical for contractile ring assembly. In neuroblasts, in contrast, Survivin function was not required for localization of Rho, Polo, or Myosin II to a broad equatorial cortical band but was required for Myosin II to transition to a compact, fully constricted ring. Analysis of this 'separation-of-function' allele demonstrates the direct role of Survivin and the CPC in cytokinesis and highlights striking differences in regulation of cytokinesis in different cell systems (Szafer-Glusman, 2011).
- Glial cell line-derived neurotrophic family receptor-like
Glial cell line-derived neurotrophic factor (GDNF) family ligands are secreted growth factors distantly related to the TGF-β superfamily. In mammals, they bind to the GDNF family receptor α (Gfrα) and signal through the Ret receptor tyrosine kinase. In order to gain insight into the evolution of the Ret-Gfr-Gdnf signaling system, the first invertebrate Gfr-like cDNA (DmGfrl) was cloned and characterized from Drosophila melanogaster, and a DmGfrl mutant allele was generated. It was found that DmGfrl encodes a large GPI-anchored membrane protein with four GFR-like domains. In line with the fact that insects lack GDNF ligands, DmGfrl mediates neither Drosophila Ret phosphorylation nor mammalian RET phosphorylation. In situ hybridization analysis revealed that DmGfrl is expressed in the central and peripheral nervous systems throughout Drosophila development, but, surprisingly, DmGfrl and DmRet expression patterns were largely non-overlapping. a DmGfrl null allele was generated by genomic FLP deletion, and it was found that both DmGfrl null females and males are viable but display fertility defects. The female fertility defect manifested as dorsal appendage malformation, small size and reduced viability of eggs laid by mutant females. In male flies DmGfrl interacted genetically with the Drosophila Ncam (neural cell adhesion molecule) homolog FasII to regulate fertility. These results suggest that Ret and Gfrl did not function as an in cis receptor-coreceptor pair before the emergence of GDNF family ligands, and that the Ncam-Gfr interaction predated the in cis Ret-Gfr interaction in evolution. The fertility defects that were describe in DmGfrl null flies suggest that GDNF receptor-like has an evolutionarily ancient role in regulating male fertility and a previously unrecognized role in regulating oogenesis. These results shed light on the evolutionary aspects of the structure, expression and function of Ret-Gfrα and Ncam-Gfrα signaling complexes (Kallijarvi, 2012).
In adult stem cell lineages, progenitor cells commonly undergo mitotic transit amplifying (TA) divisions before terminal differentiation, allowing production of many differentiated progeny per stem cell division. Mechanisms that limit TA divisions and trigger the switch to differentiation may protect against cancer by preventing accumulation of oncogenic mutations in the proliferating population. This study shows that the switch from TA proliferation to differentiation in the Drosophila male germline stem cell lineage is mediated by translational control. The TRIM-NHL tumor suppressor homolog Mei-P26 facilitates accumulation of the differentiation regulator Bam in TA cells. In turn, Bam and its partner Bgcn bind the mei-P26 3' untranslated region and repress translation of mei-P26 in late TA cells. Thus, germ cells progress through distinct, sequential regulatory states, from Mei-P26 on/Bam off to Bam on/Mei-P26 off. TRIM-NHL homologs across species facilitate the switch from proliferation to differentiation, suggesting a conserved developmentally programmed tumor suppressor mechanism (Insco, 2012).
- Painting of fourth
In Drosophila, two chromosome-wide compensatory systems have been characterized: the dosage compensation system that acts on the male X chromosome and the chromosome-specific regulation of genes located on the heterochromatic fourth chromosome. Dosage compensation in Drosophila is accomplished by hypertranscription of the single male X chromosome mediated by the male-specific lethal (MSL) complex. The mechanism of this compensation is suggested to involve enhanced transcriptional elongation mediated by the MSL complex, while the mechanism of compensation mediated by the painting of fourth (POF) protein on the fourth chromosome has remained elusive. This study shows that POF binds to nascent RNA, and this binding is associated with increased transcription output from chromosome 4. Genes located in heterochromatic regions spend less time in transition from the site of transcription to the nuclear envelope. These results provide useful insights into the means by which genes in heterochromatic regions can overcome the repressive influence of their hostile environment (Johansson, 2012).
Integrin-linked kinase (ILK), PINCH (Steamer Duck in Drosophila) and Parvin constitute the tripartite IPP complex that maintains the integrin-actin link at embryonic muscle attachment sites (MASs) in Drosophila. This study shows that parvin null mutants in Drosophila exhibit defects in muscle adhesion, similar to ILK and PINCH mutants. Furthermore, the identical muscle phenotype of the triple mutant, which for the first time in any organism removed the entire IPP-complex function, genetically demonstrated that Parvin, ILK and PINCH function synergistically. This is consistent with the tight localization of the tripartite complex at sites of integrin adhesion, namely MASs in the developing embryo and focal-contact-like structures in the wing epithelium. Parvin contains tandem unconventional calponin-homology (CH) domains separated by a linker sequence, and a less-well conserved N-terminal region. In vivo structure-function analysis revealed that all the domains are essential for Parvin function, whereas recruitment at integrin adhesion sites is mediated by two localization signals: one located within the CH2 domain as previously reported, and a second novel signal within the CH1 domain. Interestingly, this site is masked by the linker region between the two CH domains, suggesting a regulatory mechanism to control Parvin localization. Finally, whereas in muscles only ILK controls the stability and localization of both PINCH and parvin, in the wing epithelium the three proteins mutually depend on each other. Thus molecular differences exist in the assembly properties of IPP complex in specific tissues during development, where differential modulation of the integrin connection to the cytoskeleton is required (Vakaloglou, 2012).
- Phosphoinositide-dependent kinase 1
The dimensions of neuronal dendrites, axons, and synaptic terminals are reproducibly specified for each neuron type, yet it remains unknown how these structures acquire their precise dimensions of length and diameter. Similarly, it remains unknown how active zone number and synaptic strength are specified relative the precise dimensions of presynaptic boutons. This paper demonstrates that S6 kinase (S6K) localizes to the presynaptic active zone. Specifically, S6K colocalizes with the presynaptic protein Bruchpilot (Brp) and requires Brp for active zone localization. Evidence is provided that S6K functions downstream of presynaptic PDK1 to control synaptic bouton size, active zone number, and synaptic function without influencing presynaptic bouton number. It was further demonstrated that PDK1 is also a presynaptic protein, though it is distributed more broadly. A model is presented in which synaptic S6K responds to local extracellular nutrient and growth factor signaling at the synapse to modulate developmental size specification, including cell size, bouton size, active zone number, and neurotransmitter release (Cheng, 2011).
The establishment and maintenance of apical-basal cell polarity is critical for assembling epithelia and maintaining organ architecture. Drosophila embryos provide a superb model. In the current view, apically positioned Bazooka/Par3 is the initial polarity cue as cells form during cellularization. Bazooka then helps to position both adherens junctions and atypical protein kinase C (aPKC). Although a polarized cytoskeleton is critical for Bazooka positioning, proteins mediating this remained unknown. This study found that the small GTPase Rap1 and the actin-junctional linker Canoe/afadin are essential for polarity establishment, as both adherens junctions and Bazooka are mispositioned in their absence. Rap1 and Canoe do not simply organize the cytoskeleton, as actin and microtubules become properly polarized in their absence. Canoe can recruit Bazooka when ectopically expressed, but they do not obligatorily colocalize. Rap1 and Canoe play continuing roles in Bazooka localization during gastrulation, but other polarity cues partially restore apical Bazooka in the absence of Rap1 or Canoe. The current linear model for polarity establishment was tested. Both Bazooka and aPKC regulate Canoe localization despite being 'downstream' of Canoe. Further, Rap1, Bazooka, and aPKC, but not Canoe, regulate columnar cell shape. These data suggest that polarity establishment is regulated by a protein network rather than a linear pathway (Choi, 2013).
Recent studies have shown that the Hippo-Salvador-Warts (HSW) pathway restrains tissue growth by phosphorylating and inactivating the oncoprotein Yorkie. How growth-suppressive signals are transduced upstream of Hippo remains unclear. This study shows that the Sterile 20 family kinase, Tao-1, directly phosphorylates T195 in the Hippo activation loop and that, like other HSW pathway genes, Tao-1 functions to restrict cell proliferation in developing imaginal epithelia. This relationship appears to be evolutionarily conserved, because mammalian Tao-1 similarly affects MST kinases. In S2 cells, Tao-1 mediates the effects of the upstream HSW components Merlin and Expanded, consistent with the idea that Tao-1 functions in tissues to regulate Hippo phosphorylation. These results demonstrate that one family of Ste20 kinases can activate another and identify Tao-1 as a component of the regulatory network controlling HSW pathway signaling, and therefore tissue growth, during development (Boggiano, 2011).
- Tenascin accessory
Synapse assembly requires trans-synaptic signals between the pre- and postsynapse, but understanding of the essential organizational molecules involved in this process remains incomplete. Teneurin proteins are conserved, epidermal growth factor (EGF)-repeat-containing transmembrane proteins with large extracellular domains. This study shows that two Drosophila Teneurins, Ten-m and Ten-a, are required for neuromuscular synapse organization and target selection. Ten-a is presynaptic whereas Ten-m is mostly postsynaptic; neuronal Ten-a and muscle Ten-m form a complex in vivo. Pre- or postsynaptic Teneurin perturbations cause severe synapse loss and impair many facets of organization trans-synaptically and cell autonomously. These include defects in active zone apposition, release sites, membrane and vesicle organization, and synaptic transmission. Moreover, the presynaptic microtubule and postsynaptic spectrin cytoskeletons are severely disrupted, suggesting a mechanism whereby Teneurins organize the cytoskeleton, which in turn affects other aspects of synapse development. Supporting this, Ten-m physically interacts with alpha-Spectrin. Genetic analyses of teneurin and neuroligin reveal that they have differential roles that synergize to promote synapse assembly. Finally, at elevated endogenous levels, Ten-m regulates target selection between specific motor neurons and muscles. This study identifies the Teneurins as a key bi-directional trans-synaptic signal involved in general synapse organization, and demonstrates that proteins such as these can also regulate target selection (Mosca, 2012).
Tip60 is a histone acetyltransferase (HAT) enzyme that epigenetically regulates genes enriched for neuronal functions through interaction with the amyloid precursor protein (APP) intracellular domain. However, whether Tip60 mediated epigenetic dysregulation affects specific neuronal processes in vivo and contributes to neurodegeneration remains unclear. This study shows that Tip60 HAT activity mediates axonal growth of the Drosophila pacemaker cells, termed small ventrolateral neurons (sLNvs), and their production of the neuropeptide pigment dispersing factor (PDF) that functions to stabilize Drosophila sleep-wake cycles. Using genetic approaches, loss of Tip60 HAT activity in the presence of the Alzheimer's disease (AD) associated amyloid precursor protein (APP) was shown to affect PDF expression and causes retraction of the sLNv synaptic arbor required for presynaptic release of PDF. Functional consequence of these effects is evidenced by disruption of sleep-wake cycle in these flies. Notably, overexpression of Tip60 in conjunction with APP rescues these sleep-wake disturbances by inducing overelaboration of the sLNv synaptic terminals and increasing PDF levels, supporting a neuroprotective role for dTip60 on sLNv growth and function under APP induced neurodegenerative conditions. These findings reveal a novel mechanism for Tip60 mediated sleep-wake regulation via control of axonal growth and PDF levels within the sLNv encompassing neural network and provide insight into epigenetic based regulation of sleep disturbances observed in neurodegenerative diseases like Alzheimer's disease (Pirooznia, 2012b).
- Transient receptor potential mucolipin
- isruption of the TRPML1 channel results in the neurodegenerative disorder mucolipidosis type IV (MLIV), a lysosomal storage disease with severe motor impairments. The mechanisms underlying MLIV are poorly understood and there is no treatment. This study reports a Drosophila MLIV model, which recapitulates the key disease features, including abnormal intracellular accumulation of macromolecules, motor defects and neurodegeneration. The basis for the buildup of macromolecules is defective autophagy, which results in oxidative stress and impaired synaptic transmission. Late-apoptotic cells accumulate in trpml mutant brains suggesting diminished cell clearance. The accumulation of late apoptotic cells and motor deficits are suppressed by expression of trpml+ in neurons, glia or hematopoietic cells. It is concluded that the neurodegeneration and motor defects result primarily from decreased clearance of apoptotic cells. Since hematopoietic cells in humans are involved in clearance of apoptotic cells, the results raise the possibility that bone marrow transplantation may limit the progression of MLIV (Venkatachalam, 2008).
Snail family transcription factors are best known for regulating epithelial-mesenchymal transition (EMT). The Drosophila Snail family member Worniu is specifically transcribed in neural progenitors (neuroblasts) throughout their lifespan, and worniu mutants show defects in neuroblast delamination (a form of EMT). However, the role of Worniu in neuroblasts beyond their formation is unknown. RNA-seq was performed on worniu mutant larval neuroblasts, and reduced cell-cycle transcripts and increased neural differentiation transcripts were observed. Consistent with these genomic data, worniu mutant neuroblasts showed a striking delay in prophase/metaphase transition by live imaging and increased levels of the conserved neuronal differentiation splicing factor Elav. Reducing Elav levels significantly suppressed the worniu mutant phenotype. It is concluded that Worniu is continuously required in neuroblasts to maintain self-renewal by promoting cell-cycle progression and inhibiting premature differentiation (Lai, 2012).
date revised: 3 September 2013
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