What's new in edition 66 December 2012 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:

Estrogen-related receptor

Metabolism must be coordinated with development to provide the appropriate energetic needs for each stage in the life cycle. Little is known, however, about how this temporal control is achieved. This study shows that the Drosophila ortholog of the estrogen-related receptor (ERR) family of nuclear receptors directs a critical metabolic transition during development. Drosophila ERR mutants die as larvae with low ATP levels and elevated levels of circulating sugars. The expression of active dERR protein in mid-embryogenesis triggers a coordinate switch in gene expression that drives a metabolic program normally associated with proliferating cells, supporting the dramatic growth that occurs during larval development. This study shows that dERR plays a central role in carbohydrate metabolism, demonstrates that a proliferative metabolic program is used in normal developmental growth, and provides a molecular context to understand the close association between mammalian ERR family members and cancer (Tennessen, 2011).

Forkhead domain 3F

Cilia have evolved hugely diverse structures and functions to participate in a wide variety of developmental and physiological processes. Ciliary specialization requires differences in gene expression, but few transcription factors are known to regulate this, and their molecular function is unclear. This study shows that the Drosophila Forkhead box (Fox) gene, fd3F, is required for specialization of the mechanosensory cilium of chordotonal (Ch) neurons. fd3F regulates genes for Ch-specific axonemal dyneins and TRPV ion channels, which are required for sensory transduction, and retrograde transport genes, which are required to differentiate their distinct motile and sensory ciliary zones. fd3F is reminiscent of vertebrate Foxj1, a motile cilia regulator, but fd3F regulates motility genes as part of a broader sensory regulation program. Fd3F cooperates with the pan-ciliary transcription factor, Rfx, to regulate its targets directly. This illuminates pathways involved in ciliary specialization and the molecular mechanism of transcription factors that regulate them (Newton, 2010).

Gustatory receptor 66A

Understanding sensory systems that perceive environmental inputs and neural circuits that select appropriate motor outputs is essential for studying how organisms modulate behavior and make decisions necessary for survival. Drosophila melanogaster oviposition is one such important behavior, in which females evaluate their environment and choose to lay eggs on substrates they may find aversive in other contexts. This study employed neurogenetic techniques to characterize neurons that influence the choice between repulsive positional and attractive egg-laying responses toward the bitter-tasting compound lobeline. Surprisingly, it was found that neurons expressing Gr66a, a gustatory receptor normally involved in avoidance behaviors, receive input for both attractive and aversive preferences. It was hypothesized that these opposing responses may result from activation of distinct Gr66a-expressing neurons. Using tissue-specific rescue experiments, it was found that Gr66a-expressing neurons on the legs mediate positional aversion. In contrast, pharyngeal taste cells mediate the egg-laying attraction to lobeline, as determined by analysis of mosaic flies in which subsets of Gr66a neurons were silenced. Finally, inactivating mushroom body neurons disrupted both aversive and attractive responses, suggesting that this brain structure is a candidate integration center for decision-making during Drosophila oviposition. This study thus defines sensory and central neurons critical to the process by which flies decide where to lay an egg. Furthermore, the findings provide insights into the complex nature of gustatory perception in Drosophila. Tissue-specific activation of bitter-sensing Gr66a neurons provides one mechanism by which the gustatory system differentially encodes aversive and attractive responses, allowing the female fly to modulate her behavior in a context-dependent manner (Joseph, 2012).

Histone deacetylase 3

Histone acetylation is one of the best-studied gene modifications and has been shown to be involved in numerous important biological processes. This study has demonstrated that the depletion of histone deacetylase 3 (Hdac3) in Drosophila melanogaster results in a reduction in body size. Further genetic studies showed that Hdac3 counteracts the overgrowth induced by InR, PI3K or S6K over-expression, and the growth regulation by Hdac3 is mediated through the deacetylation of histone H4 at lysine 16 (H4K16). Consistently, the alterations of H4K16 acetylation (H4K16ac) induced by the over-expression or depletion of males-absent-on-the-first (MOF), a histone acetyltransferase that specifically targets H4K16, results in changes in body size. Furthermore, H4K16ac was found to be modulated by PI3K signaling cascades. The activation of the PI3K pathway caused a reduction in H4K16ac, whereas the inactivation of the PI3K pathway results in an increase in H4K16ac. The increase in H4K16ac by the depletion of Hdac3 counteracts the PI3K-induced tissue overgrowth and PI3K-mediated alterations in the transcription profile. Overall, these studies indicated that Hdac3 serves as an important regulator of the PI3K pathway and reveals a novel link between histone acetylation and growth control (Lv, 2012).

Insulin-like peptide 8

Developing animals frequently adjust their growth programs and/or their maturation or metamorphosis to compensate for growth disturbances (such as injury or tumor) and ensure normal adult size. Such plasticity entails tissue and organ communication to preserve their proportions and symmetry. Imaginal discs autonomously activate DILP8, a Drosophila insulin-like peptide, to communicate abnormal growth and postpone maturation. DILP8 delays metamorphosis by inhibiting ecdysone biosynthesis, slowing growth in the imaginal discs, and generating normal-sized animals. Loss of dilp8 yields asymmetric individuals with an unusually large variation in size and a more varied time of maturation. Thus, DILP8 is a fundamental element of the hitherto ill-defined machinery governing the plasticity that ensures developmental stability and robustness (Garelli, 2012).

Lateral muscles scarcer

Patterning and differentiation of developing musculatures require elaborate networks of transcriptional regulation. In Drosophila, significant progress has been made into identifying the regulators of muscle development and defining their interactive networks. One major family of transcription factors involved in these processes consists of homeodomain proteins. In flies, several members of this family serve as muscle identity genes to specify the fates of individual muscles, or groups thereof, during embryonic and/or adult muscle development. This study reports on the expression and function of a new Drosophila homeobox gene during both embryonic and adult muscle development. The newly described homeobox gene, termed lateral muscles scarcer (lms), which has yet uncharacterized orthologs in other invertebrates and primitive chordates but not in vertebrates, is expressed exclusively in subsets of developing muscle tissues. In embryos, lms is expressed specifically in the four lateral transverse (LT) muscles and their founder cells in each hemisegment, whereas in larval wing imaginal discs, it is expressed in myoblasts that develop into direct flight muscles (DFMs), which are important for proper wing positioning. The regulatory inputs of various other muscle identity genes with overlapping or complementary expression patterns towards the cell type specific regulation of lms expression were analyzed. Further it was demonstrate that lms null mutants exhibit reduced numbers of embryonic LT muscles, and null mutant adults feature held-out-wing phenotypes. A detailed description is provided of the pattern and morphology of the direct flight muscles in the wild type and lms mutant flies by using the recently-developed ultramicroscopy, and it was shown that, in the mutants, all DFMs are present and present normal morphologies. This study has identified the homeobox gene lms as a new muscle identity gene and shows that it interacts with various previously-characterized muscle identity genes to regulate normal formation of embryonic lateral transverse muscles. In addition, the direct flight muscles in the adults require lms for reliably exerting their functions in controlling wing postures (Müller, 2010).

Leucokinin receptor

Total food intake is a function of meal size and meal frequency, and adjustments to these parameters allow animals to maintain a stable energy balance in changing environmental conditions. The physiological mechanisms that regulate meal size have been studied in blowflies but have not been previously examined in Drosophila. This study shows that mutations in the leucokinin neuropeptide (leuc) and leucokinin receptor (lkr) genes cause phenotypes in which Drosophila adults have an increase in meal size and a compensatory reduction in meal frequency. Since mutant flies take larger but fewer meals, their caloric intake is the same as that of wild-type flies. The expression patterns of the leuc and lkr genes identify small groups of brain neurons that regulate this behavior. Leuc-containing presynaptic terminals are found close to Lkr neurons in the brain and ventral ganglia, suggesting that they deliver Leuc peptide to these neurons. Lkr neurons innervate the foregut. Flies in which Leuc or Lkr neurons are ablated have defects identical to those of leucokinin pathway mutants. These data suggest that the increase in meal size in leuc and lkr mutants is due to a meal termination defect, perhaps arising from impaired communication of gut distension signals to the brain. Leucokinin and the leucokinin receptor are homologous to vertebrate tachykinin and its receptor, and injection of tachykinins reduces food consumption. These results suggest that the roles of the tachykinin system in regulating food intake might be evolutionarily conserved between insects and vertebrates (Al-Anzi, 2011).

Liquid facets-Related

Epsin and epsin-Related (epsinR) are multi-modular proteins that stimulate clathrin-coated vesicle formation. Epsin promotes endocytosis at the plasma membrane, and epsinR functions at the Golgi and early endosomes for trans-Golgi network/endosome vesicle trafficking. In Drosophila, endocytic epsin is known as Liquid facets, and it is essential specifically for Notch signaling. By generating and analyzing loss-of-function mutants in the liquid facets-Related (lqfR) gene of Drosophila, this study investigated the function of Golgi epsin in a multicellular context. LqfR was found to be a Golgi protein, and like liquid facets, lqfR is essential for Drosophila viability. In addition, primarily by analyzing mutant eye discs, it was found that lqfR is required for cell proliferation, insulin-independent cell growth, and cell patterning, consistent with a role in one or several signaling pathways. Epsins in all organisms share an ENTH (epsin N terminal homology) domain, which binds phosphoinositides enriched at the plasma membrane or the Golgi membrane. The epsinR ENTH domain is also the recognition element for particular cargos. By generating wild-type and mutant lqfR transgenes, it was found that all apparent LqfR functions are independent of its ENTH domain. These results suggest that LqfR transports specific cargo critical to one or more signaling pathways, and lays the foundation for identifying those proteins (Lee, 2009).

Lost PHDs of trr

MLL2 and MLL3 histone lysine methyltransferases are conserved components of COMPASS-like co-activator complexes. In vertebrates, the paralogous MLL2 and MLL3 contain multiple domains required for epigenetic reading and writing of the histone code involved in hormone-stimulated gene programming, including receptor-binding motifs, SET methyltransferase, HMG and PHD domains. The genes encoding MLL2 and MLL3 arose from a common ancestor. Phylogenetic analyses reveal that the ancestral gene underwent a fission event in some Brachycera dipterans, including Drosophila species, creating two independent genes corresponding to the N- and C-terminal portions. In Drosophila, the C-terminal SET domain is encoded by trithorax-related (trr), which is required for hormone-dependent gene activation. This study identified the cara mitad (cmi) gene, which encodes the previously undiscovered N-terminal region consisting of PHD and HMG domains and receptor-binding motifs. The cmi gene is essential and its functions are dosage sensitive. CMI associates with TRR, as well as the EcR-USP receptor, and is required for hormone-dependent transcription. Unexpectedly, although the CMI and MLL2 PHDf3 domains could bind histone H3, neither showed preference for trimethylated lysine 4. Genetic tests reveal that cmi is required for proper global trimethylation of H3K4 and that hormone-stimulated transcription requires chromatin binding by CMI, methylation of H3K4 by TRR and demethylation of H3K27 by the demethylase UTX. The evolutionary split of MLL2 into two distinct genes in Drosophila provides important insight into distinct epigenetic functions of conserved readers and writers of the histone code (Chauhan, 2012).

Metabotrophic glutamate receptor

In vertebrates, several groups of metabotropic glutamate receptors (mGluRs) are known to modulate synaptic properties. In contrast, the Drosophila genome encodes a single functional mGluR (DmGluRA), an ortholog of vertebrate group II mGluRs, greatly expediting the functional characterization of mGluR-mediated signaling in the nervous system. This study shows that DmGluRA is expressed at the glutamatergic neuromuscular junction (NMJ), localized in periactive zones of presynaptic boutons but excluded from active sites. Null DmGluRA mutants are completely viable, and all of the basal NMJ synaptic transmission properties are normal. In contrast, DmGluRA mutants display approximately a threefold increase in synaptic facilitation during short stimulus trains. Prolonged stimulus trains result in very strongly increased (approximately 10-fold) augmentation, including the appearance of asynchronous, bursting excitatory currents never observed in wild type. Both defects are rescued by expression of DmGluRA only in the neurons, indicating a specific presynaptic requirement. These phenotypes are reminiscent of hyperexcitable mutants, suggesting a role of DmGluRA signaling in the regulation of presynaptic excitability properties. The mutant phenotypes could not be replicated by acute application of mGluR antagonists, suggesting that DmGluRA regulates the development of presynaptic properties rather than directly controlling short-term modulation. DmGluRA mutants also display mild defects in NMJ architecture: a decreased number of synaptic boutons accompanied by an increase in mean bouton size. These morphological changes bidirectionally correlate with DmGluRA levels in the presynaptic terminal. These data reveal the following two roles for DmGluRA in presynaptic mechanisms: (1) modulation of presynaptic excitability properties important for the control of activity-dependent neurotransmitter release and (2) modulation of synaptic architecture (Bogdanik, 2004).

Mon2

Drosophila pole (germ) plasm contains germline and abdominal determinants. Its assembly begins with the localization and translation of oskar (osk) RNA at the oocyte posterior, to which the pole plasm must be restricted for proper embryonic development. Osk stimulates endocytosis, which in turn promotes actin remodeling to form long F-actin projections at the oocyte posterior pole. Although the endocytosis-coupled actin remodeling appears to be crucial for the pole plasm anchoring, the mechanism linking Osk-induced endocytic activity and actin remodeling is unknown. This study reports that a Golgi-endosomal protein, Mon2, acts downstream of Osk to remodel cortical actin and to anchor the pole plasm. Mon2 interacts with two actin nucleators known to be involved in osk RNA localization in the oocyte, Cappuccino (Capu) and Spire (Spir), and promotes the accumulation of the small GTPase Rho1 at the oocyte posterior. This study also found that these actin regulators are required for Osk-dependent formation of long F-actin projections and cortical anchoring of pole plasm components. It is proposed that, in response to the Osk-mediated endocytic activation, vesicle-localized Mon2 acts as a scaffold that instructs the actin-remodeling complex to form long F-actin projections. This Mon2-mediated coupling event is crucial to restrict the pole plasm to the oocyte posterior cortex (Tanaka, 2011).

Myoglianin

Glia secrete myoglianin, a TGF-β ligand, to instruct developmental neural remodeling in Drosophila. Glial myoglianin upregulates neuronal expression of an ecdysone nuclear receptor that triggers neurite remodeling following the late-larval ecdysone peak. Thus glia orchestrate developmental neural remodeling not only by engulfment of unwanted neurites but also by enabling neuron remodeling (Awasaki, 2011).

Neither inactivation nor afterpotential C

Upon illumination several phototransduction proteins translocate between cell body and photosensory compartments. In Drosophila photoreceptors arrestin (Arr2) translocates from cell body to the microvillar rhabdomere down a diffusion gradient created by binding of Arr2 to photo-isomerized metarhodopsin. Translocation is profoundly slowed in mutants of key phototransduction proteins including phospholipase C (PLC) and the Ca(2+)-permeable transient receptor potential channel (TRP), but how the phototransduction cascade accelerates Arr2 translocation is unknown. Using real-time fluorescent imaging of Arr2-green fluorescent protein translocation in dissociated ommatidia, this study shows that translocation is profoundly slowed in Ca(2+)-free solutions. Conversely, in a blind PLC mutant with ~100-fold slower translocation, rapid translocation was rescued by the Ca(2+) ionophore, ionomycin. In mutants lacking NINAC (calmodulin [CaM] binding myosin III) in the cell body, translocation remained rapid even in Ca(2+)-free solutions. Immunolabeling revealed that Arr2 in the cell body colocalizes with NINAC in the dark. In intact eyes, the impaired translocation found in trp mutants was rescued in ninaC;trp double mutants. Nevertheless, translocation following prolonged dark adaptation was significantly slower in ninaC mutants, than in wild type: a difference that was reflected in the slow decay of the electroretinogram. The results suggest that cytosolic NINAC is a Ca(2+)-dependent binding target for Arr2, which protects Arr2 from immobilization by a second potential sink that sequesters and releases arrestin on a much slower timescale. It is proposed that rapid Ca(2+)/CaM-dependent release of Arr2 from NINAC upon Ca(2+) influx accounts for the acceleration of translocation by phototransduction (Hardie, 2012).

Nucleoporin 44A

The nuclear pore complex (NPC) mediates the transport of macromolecules between the nucleus and cytoplasm. Recent evidence indicates that structural nucleoporins, the building blocks of the NPC, have a variety of unanticipated cellular functions. This study reports an unexpected tissue-specific requirement for the structural nucleoporin Seh1 during Drosophila oogenesis. Seh1 is a component of the Nup107-160 complex, the major structural subcomplex of the NPC. Seh1 associates with the product of the missing oocyte (mio) gene. In Drosophila, mio regulates nuclear architecture and meiotic progression in early ovarian cysts. Like mio, seh1 has a crucial germline function during oogenesis. In both mio and seh1 mutant ovaries, a fraction of oocytes fail to maintain the meiotic cycle and develop as pseudo-nurse cells. Moreover, the accumulation of Mio protein is greatly diminished in the seh1 mutant background. Surprisingly, characterization of a seh1 null allele indicates that, although required in the female germline, seh1 is dispensable for the development of somatic tissues. This work represents the first examination of seh1 function within the context of a multicellular organism. Seh1 has been shown to play a role in the construction and/or maintenance of bipolar spindles in multiple organisms. In summary, these studies demonstrate that Mio is a novel interacting partner of the conserved nucleoporin Seh1 and add to the growing body of evidence that structural nucleoporins can have novel tissue-specific roles (Senger, 2011).

Numb-associated kinase

During development, dendrites arborize in a field several hundred folds of their soma size, a process regulated by intrinsic transcription program and cell adhesion molecule (CAM)-mediated interaction. However, underlying cellular machineries that govern distal higher-order dendrite extension remain largely unknown. This study shows that Numb-associated kinase (Nak), a clathrin adaptor-associated kinase, promotes higher-order dendrite growth through endocytosis. In nak mutants, both the number and length of higher-order dendrites are reduced; these characters phenocopied by disruptions of clathrin-mediated endocytosis. Nak interacts genetically with components of the endocytic pathway, colocalizes with clathrin puncta and is required for dendritic localization of clathrin puncta. More importantly, these Nak-containing clathrin structures preferentially localize to branching points and dendritic tips that are undergoing active growth. Evidence is presented that the Drosophila L1-CAM homolog Neuroglian is a relevant cargo of Nak-dependent internalization, suggesting that localized clathrin-mediated endocytosis of CAMs facilitates the extension of nearby higher-order dendrites (Yang, 2011).

Paxillin

Paxillin is a prominent focal adhesion docking protein that regulates cell adhesion and migration. Although numerous paxillin-binding proteins have been identified and paxillin is required for normal embryogenesis, the precise mechanism by which paxillin functions in vivo has not yet been determined. An ortholog of mammalian paxillin in Drosophila (Dpax) has been identified and a genetic analysis of paxillin function during development was undertaken. Overexpression of Dpax disrupts leg and wing development, suggesting a role for paxillin in imaginal disc morphogenesis. These defects may reflect a function for paxillin in regulation of Rho family GTPase signaling since paxillin interacts genetically with Rac and Rho in the developing eye. Moreover, a gain-of-function suppressor screen identified a genetic interaction between Dpax and center divider cdi in wing development. Cdi belongs to the cofilin kinase family, which includes the downstream Rho target, LIM kinase (LIMK). Significantly, strong genetic interactions were detected between Dpax and Dlimk, as well as downstream effectors of Dlimk. Supporting these genetic data, biochemical studies indicate that paxillin regulates Rac and Rho activity, positively regulating Rac and negatively regulating Rho. Taken together, these data indicate the importance of paxillin modulation of Rho family GTPases during development and identify the LIMK pathway as a critical target of paxillin-mediated Rho regulation (Chen, 2005).

Pecanex

The Notch (N) signaling machinery is evolutionarily conserved and regulates a broad spectrum of cell-specification events, through local cell-cell communication. pecanex (pcx) encodes a multi-pass transmembrane protein of unknown function, widely found from Drosophila to humans. The zygotic and maternal loss of pcx in Drosophila causes a neurogenic phenotype (hyperplasia of the embryonic nervous system), suggesting that pcx might be involved in N signaling. This study has established that pcx is a component of the N-signaling pathway. pcx is required upstream of the membrane-tethered and the nuclear forms of activated N, probably in N signal-receiving cells, suggesting that pcx is required prior to or during the activation of N. pcx overexpression revealed that pcx resides in the endoplasmic reticulum (ER). Disruption of pcx function results in enlargement of the ER that is not attributable to the reduced N signaling activity. In addition, hyper-induction of the unfolded protein response (UPR) by the expression of activated Xbp1 or dominant-negative Heat shock protein cognate 3 suppresses the neurogenic phenotype and ER enlargement caused by the absence of pcx. A similar suppression of these phenotypes is induced by overexpression of O-fucosyltransferase 1, an N-specific chaperone. Taking these results together, it is speculated that the reduction in N signaling in embryos lacking pcx function might be attributable to defective ER functions, which are compensated for by upregulation of the UPR and possibly by enhancement of N folding. These results indicate that the ER plays a previously unrecognized role in N signaling and that this ER function depends on pcx activity (Yamakawa, 2012).

Trithorax-related

Methylation of histone H3 lysine 4 (H3K4) in Saccharomyces cerevisiae is implemented by Set1/COMPASS (Complex Proteins Associated with Set1), which was originally purified based on the similarity of yeast Set1 to human MLL1 and Drosophila (Trx). While humans have six COMPASS family members, Drosophila has a representative of the three subclasses within COMPASS-like complexes: dSet1 (human SET1A/SET1B), Trx (human MLL1/2), and Trr (human MLL3/4), the subject of this web-site. This study reports the biochemical purification and molecular characterization of the Drosophila COMPASS family. A one-to-one similarity occurs in subunit composition with their mammalian counterparts, with the exception of (lost plant homeodomains [PHDs] of Trr), which copurifies with the Trr complex. LPT is a previously uncharacterized protein that is homologous to the multiple PHD fingers found in the N-terminal regions of mammalian MLL3/4 but not Drosophila Trr, indicating that Trr and LPT constitute a split gene of an MLL3/4 ancestor. This study demonstrates that all three complexes in Drosophila are H3K4 methyltransferases; however, dSet1/COMPASS is the major monoubiquitination-dependent H3K4 di- and trimethylase in Drosophila. Taken together, this study provides a springboard for the functional dissection of the COMPASS family members and their role in the regulation of histone H3K4 methylation throughout development in Drosophila (Mohan, 2011).

Home page: The Interactive Fly © 2012 Thomas B. Brody, Ph.D.

The Interactive Fly resides on the
Society for Developmental Biology's Web server.