What's new in edition 71 September 2014 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:

alan shepard

Chromatin insulators organize the genome into distinct transcriptional domains and contribute to cell type-specific chromatin organization. However, factors regulating tissue-specific insulator function have not yet been discovered. This study identified the RNA recognition motif-containing protein Shep as a direct interactor of two individual components of the gypsy insulator complex in Drosophila. Mutation of shep improves gypsy-dependent enhancer blocking, indicating a role as a negative regulator of insulator activity. Unlike ubiquitously expressed core gypsy insulator proteins, Shep is highly expressed in the central nervous system (CNS) with lower expression in other tissues. A novel, quantitative tissue-specific barrier assay was developed to demonstrate that Shep functions as a negative regulator of insulator activity in the CNS but not in muscle tissue. Additionally, mutation of shep alters insulator complex nuclear localization in the CNS but has no effect in other tissues. Consistent with negative regulatory activity, ChIP-seq analysis of Shep in a CNS-derived cell line indicates substantial genome-wide colocalization with a single gypsy insulator component but limited overlap with intact insulator complexes. Taken together, these data reveal a novel, tissue-specific mode of regulation of a chromatin insulator (Matzat, 2012).

cabeza

Mutations in the fused in sarcoma/translated in liposarcoma gene (FUS/TLS, FUS) have been identified in sporadic and familial forms of amyotrophic lateral sclerosis (ALS). FUS is an RNA-binding protein that is normally localized in the nucleus, but is mislocalized to the cytoplasm in ALS, and comprises cytoplasmic inclusions in ALS-affected areas. However, it is still unknown whether the neurodegeneration that occurs in ALS is caused by the loss of FUS nuclear function, or by the gain of toxic function due to cytoplasmic FUS aggregation. Cabeza (Caz) is a Drosophila orthologue of human FUS. This study generated Drosophila models with Caz knockdown, and investigated their phenotypes. In wild-type Drosophila, Caz was strongly expressed in the central nervous system of larvae and adults. Caz did not colocalize with a presynaptic marker, suggesting that Caz physiologically functions in neuronal cell bodies and/or their axons. Fly models with neuron-specific Caz knockdown exhibited reduced climbing ability in adulthood and anatomical defects in presynaptic terminals of motoneurons in third instar larvae. The results demonstrated that decreased expression of Drosophila Caz is sufficient to cause degeneration of motoneurons and locomotive disability in the absence of abnormal cytoplasmic Caz aggregates, suggesting that the pathogenic mechanism underlying FUS-related ALS should be ascribed more to the loss of physiological FUS functions in the nucleus than to the toxicity of cytoplasmic FUS aggregates. Since the Caz-knockdown Drosophila model presented in this study recapitulates key features of human ALS, it would be a suitable animal model for the screening of genes and chemicals that might modify the pathogenic processes that lead to the degeneration of motoneurons in ALS (Sasayama, 2012).

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).

Gcn2

The brain is the central organizer of food intake, matching the quality and quantity of the food sources with organismal needs. To ensure appropriate amino acid balance, many species reject a diet lacking one or several essential amino acids (EAAs) and seek out a better food source. This study shows that, in Drosophila larvae, this behavior relies on innate sensing of amino acids in dopaminergic (DA) neurons of the brain. The amino acid sensor GCN2 acts upstream of GABA signaling in DA neurons to promote avoidance of the EAA-deficient diet. Using real-time calcium imaging in larval brains, this study shows that amino acid imbalance induces a rapid and reversible activation of three DA neurons that are necessary and sufficient for food rejection. Taken together, these data identify a central amino-acid-sensing mechanism operating in specific DA neurons and controlling food intake (Bjordal, 2014).

Gustatory receptor 43a

Internal nutrient sensors play important roles in feeding behavior, yet their molecular structure and mechanism of action are poorly understood. Using Ca²⁺ imaging and behavioral assays, this study shows that the gustatory receptor 43a (Gr43a) functions as a narrowly tuned fructose receptor in taste neurons. Remarkably, Gr43a also functions as a fructose receptor in the brain. Interestingly, hemolymph fructose levels are tightly linked to feeding status: after nutritious carbohydrate consumption, fructose levels rise several fold and reach a concentration sufficient to activate Gr43a in the brain. By using different feeding paradigms and artificial activation of Gr43a-expressing brain neurons, this study shows that Gr43a is both necessary and sufficient to sense hemolymph fructose and promote feeding in hungry flies but suppress feeding in satiated flies. Thus, these studies indicate that the Gr43a-expressing brain neurons function as a nutrient sensor for hemolymph fructose and assign opposing valence to feeding experiences in a satiation-dependent manner (Miyamoto, 2012).

lin-28

Understanding the control of stem cell (SC) differentiation is important to comprehend developmental processes as well as to develop clinical applications. Lin28 is a conserved molecule that is involved in SC maintenance and differentiation by regulating let-7 miRNA maturation. However, little is known about the in vivo function of Lin28. This study reports critical roles for lin-28 during oogenesis. let-7 maturation was shown to be increased in lin-28 null mutant fly ovaries. lin-28 null mutant female flies display reduced fecundity, due to defects in egg chamber formation. More specifically, in mutant ovaries, the egg chambers were shown to fuse during early oogenesis resulting in abnormal late egg chambers. This phenotype is the combined result of impaired germline SC differentiation and follicle SC differentiation. A model is suggested in which these multiple oogenesis defects result from a misregulation of the ecdysone signaling network, through the fine-tuning of Abrupt and Fasciclin2 expression. These results give a better understanding of the evolutionarily conserved role of lin-28 on GSC maintenance and differentiation (Stratoulias, 2014).

luna

Krüppel like factors (KLFs) are conserved transcription factors that have been implicated in many developmental processes including differentiation, organ patterning, or regulation of stem cell pluripotency. This study reports the generation and analysis of loss-of-function mutants of Drosophila Klf6/7, the luna gene. luna mutants are associated with very early embryonic defects prior to cellularization at the syncytial stage and cause DNA separation defects during the rapid mitotic cycles resulting in un-coupled DNA and centrosome cycles. These defects manifest themselves, both in animals that are maternally homozygous and heterozygous mutant. Surprisingly, luna is only required during the syncytial stages and not later in development, suggesting that the DNA segregation defect is linked to centrosomes, since centrosomes are dispensable for later cell divisions (Weber, 2014).

Mediator complex subunit 19

Hox genes in species across the metazoa encode transcription factors (TFs) containing highly-conserved homeodomains that bind target DNA sequences to regulate batteries of developmental target genes. DNA-bound Hox proteins, together with other TF partners, induce an appropriate transcriptional response by RNA Polymerase II (PolII) and its associated general transcription factors. How the evolutionarily conserved Hox TFs interface with this general machinery to generate finely regulated transcriptional responses remains obscure. One major component of the PolII machinery, the Mediator (MED) transcription complex, is composed of roughly 30 protein subunits xized in modules that bridge the PolII enzyme to DNA-bound TFs. This study investigate the physical and functional interplay between Drosophila melanogaster Hox developmental TFs and MED complex proteins. The Med19 subunit was found to directly bind Hox homeodomains, in vitro and in vivo. Loss-of-function Med19 mutations act as dose-sensitive genetic modifiers that synergistically modulate Hox-directed developmental outcomes. Using clonal analysis, a role was identified for Med19 in Hox-dependent target gene activation. A conserved, animal-specific motif was found that is required for Med19 homeodomain binding, and for activation of a specific Ultrabithorax target. These results provide the first direct molecular link between Hox homeodomain proteins and the general PolII machinery. They support a role for Med19 as a PolII holoenzyme-embedded 'co-factor' that acts together with Hox proteins through their homeodomains in regulated developmental transcription (Boube, 2014).

mir-9a stem loop

Hox genes in species across the metazoa encode transcription factors (TFs) containing highly-conserved homeodomains that bind target DNA sequences to regulate batteries of developmental target genes. DNA-bound Hox proteins, together with other TF partners, induce an appropriate transcriptional response by RNA Polymerase II (PolII) and its associated general transcription factors. How the evolutionarily conserved Hox TFs interface with this general machinery to generate finely regulated transcriptional responses remains obscure. One major component of the PolII machinery, the Mediator (MED) transcription complex, is composed of roughly 30 protein subunits xized in modules that bridge the PolII enzyme to DNA-bound TFs. This study investigate the physical and functional interplay between Drosophila melanogaster Hox developmental TFs and MED complex proteins. The Med19 subunit was found to directly bind Hox homeodomains, in vitro and in vivo. Loss-of-function Med19 mutations act as dose-sensitive genetic modifiers that synergistically modulate Hox-directed developmental outcomes. Using clonal analysis, a role was identified for Med19 in Hox-dependent target gene activation. A conserved, animal-specific motif was found that is required for Med19 homeodomain binding, and for activation of a specific Ultrabithorax target. These results provide the first direct molecular link between Hox homeodomain proteins and the general PolII machinery. They support a role for Med19 as a PolII holoenzyme-embedded 'co-factor' that acts together with Hox proteins through their homeodomains in regulated developmental transcription (Boube, 2014).

optic ganglion reduced & Innexin 2

Neural stem cells in the adult brain exist primarily in a quiescent state but are reactivated in response to changing physiological conditions. How do stem cells sense and respond to metabolic changes? In the Drosophila CNS, quiescent neural stem cells are reactivated synchronously in response to a nutritional stimulus. Feeding triggers insulin production by blood-brain barrier glial cells, activating the insulin/insulin-like growth factor pathway in underlying neural stem cells and stimulating their growth and proliferation. This study shows that gap junction proteins, Inx1 and Inx2, in the blood-brain barrier glia mediate the influence of metabolic changes on stem cell behavior, enabling glia to respond to nutritional signals and reactivate quiescent stem cells. It is proposed that gap junctions in the blood-brain barrier are required to translate metabolic signals into synchronized calcium pulses and insulin secretion (Speder, 2014).

stumble

Animal locomotion depends on proprioceptive feedback, which is generated by mechanosensory neurons. A genetic screen for impaired walking was performed in Drosophila, and a gene, stumble (stum), was isolated. The Stum protein has orthologs in animals ranging from nematodes to mammals and is predicted to contain two transmembrane domains. Expression of the mouse orthologs of stum in mutant flies rescued their phenotype, which demonstrates functional conservation. Dendrites of stum-expressing neurons in legs were stretched by both flexion and extension of corresponding joints. Joint angles that induced dendritic stretching also elicited elevation of cellular Ca(2+) levels-not seen in stum mutants. Thus, this study has identified an evolutionarily conserved gene, stum, which is required for transduction of mechanical stimuli in a specific subpopulation of Drosophila proprioceptive neurons that sense joint angles (Desai, 2014).

Synaptotagmin 4

The molecular pathways involved in retrograde signal transduction at synapses and the function of retrograde communication are poorly understood. This study demonstrates that postsynaptic calcium 2+ ion (Ca2+) influx through glutamate receptors and subsequent postsynaptic vesicle fusion trigger a robust induction of presynaptic miniature release after high-frequency stimulation at Drosophila neuromuscular junctions. An isoform of the synaptotagmin family, synaptotagmin 4 (Syt 4), serves as a postsynaptic Ca2+ sensor to release retrograde signals that stimulate enhanced presynaptic function through activation of the cyclic adenosine monophosphate (cAMP)-cAMP-dependent protein kinase pathway. Postsynaptic Ca2+ influx also stimulates local synaptic differentiation and growth through Syt 4-mediated retrograde signals in a synapse-specific manner (Yoshihara, 2005).

Vacuolar protein sorting 35

The evolutionarily conserved apical determinant Crumbs (Crb) is essential for maintaining apicobasal polarity and integrity of many epithelial tissues. Crb levels are crucial for cell polarity and homeostasis, yet strikingly little is known about its trafficking or the mechanism of its apical localization. Using a newly established, liposome-based system described in this study, Crb was determined to be an interaction partner and cargo of the retromer complex (See Retromer-mediated sorting). Retromer is essential for the retrograde transport of numerous transmembrane proteins from endosomes to the trans-Golgi network (TGN) and is conserved between plants, fungi, and animals. Loss of retromer function results in a substantial reduction of Crb in Drosophila larvae, wing discs, and the follicle epithelium. Moreover, loss of retromer phenocopies loss of crb by preventing apical localization of key polarity molecules, such as atypical protein kinase C (aPKC) and Par6 in the follicular epithelium, an effect that can be rescued by overexpression of Crb. Additionally, loss of retromer results in multilayering of the follicular epithelium, indicating that epithelial integrity is severely compromised. These data reveal a mechanism for Crb trafficking by retromer that is vital for maintaining Crb levels and localization. A novel function is also shown for retromer in maintaining epithelial cell polarity (Pocha, 2011).

wide awake

Asymmetric cell division (ACD) is a key process that allows different cell types to be generated at precisely defined times and positions. In Drosophila, neural precursor cells rely heavily on ACD to generate the different cell types in the nervous system. A conserved protein machinery that regulates ACD has been identified in Drosophila, but how this machinery acts to allow the establishment of differential cell fates is not entirely understood. To identify additional proteins required for ACD, an in vivo live imaging RNAi screen was carried out for genes affecting the asymmetric segregation of Numb in Drosophila sensory organ precursor cells. Banderuola (Bnd / Wide Awake) was identified an essential regulator of cell polarization, spindle orientation, and asymmetric protein localization in Drosophila neural precursor cells. Genetic and biochemical experiments show that Bnd acts together with the membrane-associated tumor suppressor Discs-large (Dlg) to establish antagonistic cortical domains during ACD. Inhibiting Bnd strongly enhances the dlg phenotype, causing massive brain tumors upon knockdown of both genes. Because the mammalian homologs of Bnd and Dlg are interacting as well, Bnd function might be conserved in vertebrates, and it might also regulate cell polarity in higher organisms. It is concluded that Bnd is a novel regulator of ACD in different types of cells. The data place Bnd at the top of the hierarchy of the factors involved in ACD, suggesting that its main function is to mediate the localization and function of the Dlg tumor suppressor. Bnd has an antioncogenic function that is redundant with Dlg, and the physical interaction between the two proteins is conserved in evolution (Mauri, 2014).

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