What's new in edition 51 part December 2007 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:

Argonaute 3

Drosophila Piwi-family proteins have been implicated in transposon control. This study examined piwi-interacting RNAs (piRNAs) associated with each Drosophila Piwi protein; Piwi and Aubergine were found to bind RNAs that are predominantly antisense to transposons, whereas Ago3 complexes contain predominantly sense piRNAs. As in mammals, the majority of Drosophila piRNAs are derived from discrete genomic loci. These loci comprise mainly defective transposon sequences, and some have previously been identified as master regulators of transposon activity. These data suggest that heterochromatic piRNA loci interact with potentially active, euchromatic transposons to form an adaptive system for transposon control. Complementary relationships between sense and antisense piRNA populations suggest an amplification loop wherein each piRNA-directed cleavage event generates the 5' end of a new piRNA. Thus, sense piRNAs, formed following cleavage of transposon mRNAs may enhance production of antisense piRNAs, complementary to active elements, by directing cleavage of transcripts from master control loci (Brennecke, 2007).

Clockwork orange

Many organisms use circadian clocks to keep temporal order and anticipate daily environmental changes. In Drosophila, the master clock gene Clock promotes the transcription of several key target genes. Two of these gene products, Per and Tim, repress Clk-Cyc-mediated transcription. To recognize additional direct Clk target genes, a genome-wide approach was designed and clockwork orange (cwo) was identified as a new core clock component. cwo encodes a transcriptional repressor that synergizes with Per and inhibits Clk-mediated activation. Consistent with this function, the mRNA profiles of Clk direct target genes in cwo mutant flies manifest high trough values and low amplitude oscillations. Because behavioral rhythmicity fails to persist in constant darkness (DD) with little or no effect on average mRNA levels in flies lacking cwo, transcriptional oscillation amplitude appears to be linked to rhythmicity. Moreover, the mutant flies are long period, consistent with the late repression indicated by the RNA profiles. These findings suggest that Cwo acts preferentially in the late night to help terminate Clk-Cyc-mediated transcription of direct target genes including cwo itself. The presence of mammalian homologs with circadian expression features (Dec1 and Dec2) suggests that a similar feedback mechanism exists in mammalian clocks (Kadener, 2007). To other studies similarly identified Clockwork orange an a transcriptional repressor that inhibits Clk-mediated activation (Matsumoto, 2007; Lim, 2007).

Dopamine receptor

Drosophila has robust behavioral plasticity to avoid or prefer the odor that predicts punishment or food reward, respectively. Both types of plasticity are mediated by the mushroom body (MB) neurons in the brain, in which various signaling molecules play crucial roles. However, important yet unresolved molecules are the receptors that initiate aversive or appetitive learning cascades in the MB. D1 dopamine receptor dDA1 (FlyBase name: Dopamine receptor) has been shown to be highly enriched in the MB neuropil. This study demonstrates that dDA1 is a key receptor that mediates both aversive and appetitive learning in pavlovian olfactory conditioning. Two mutants, dumb1 and dumb2, have abnormal dDA1 expression. When trained with the same conditioned stimuli, both dumb alleles showed negligible learning in electric shock-mediated conditioning while they exhibited moderately impaired learning in sugar-mediated conditioning. These phenotypes are not attributable to anomalous sensory modalities of dumb mutants because their olfactory acuity, shock reactivity, and sugar preference are comparable to those of control lines. Remarkably, the dumb mutant's impaired performance in both paradigms is fully rescued by reinstating dDA1 expression in the same subset of MB neurons, indicating the critical roles of the MB dDA1 in aversive as well as appetitive learning. Previous studies using dopamine receptor antagonists implicate the involvement of D1/D5 receptors in various pavlovian conditioning tasks in mammals; however, these have not been supported by the studies of D1- or D5-deficient animals. The findings described in this study here unambiguously clarify the critical roles of D1 dopamine receptor in aversive and appetitive pavlovian conditioning (Kim, 2007b).

Ebony

ebony encodes an β-alanyl-dopamine synthase regulating β-alanyl conjugation of dopamine and histamine, thus 'trapping' these biogenic amines preventing their further function (see Borycz, 2002 and Richardt, 2003). This enzymatic activity regulates fly pigmentation, photoreceptor activity and behavioral rhythmicity. It has been suggested that glia may be required for normal circadian behavior, but glial factors required for rhythmicity have not been identified in any system. This study shows that a circadian rhythm in Drosophila Ebony (N-β-alanyl-biogenic amine synthetase) abundance can be visualized in adult glia and that glial expression of Ebony rescues the altered circadian behavior of ebony mutants. Molecular oscillator function and clock neuron output are normal in ebony mutants, verifying a role for Ebony downstream of the clock. Surprisingly, the ebony oscillation persists in flies lacking PDF neuropeptide, indicating it is regulated by an autonomous glial oscillator or another neuronal factor. The proximity of Ebony-containing glia to aminergic neurons and genetic interaction results suggest a function in dopaminergic signaling. A model for ebony function is presented wherein Ebony glia participate in the clock control of dopaminergic function and the orchestration of circadian activity rhythms (Suh, 2007).

Eggless

SET domain proteins are histone lysine methyltransferases (HMTs) that play essential roles in development. Histone methylation occurs in both the germ cells and somatic cells of the Drosophila ovary. The product of the eggless (egg) gene, an HMT, is required for oogenesis. Egg is a SET domain protein that is similar to the human protein SETDB1 and its mouse ortholog ESET. These proteins are members of a small family of HMTs that contain bifurcated SET domains. Because depletion of SETDB1 in tissue culture cells is cell-lethal, and an ESET mutation causes very early periimplantation embryonic arrest, the role of SETDB1/ESET in development has proven difficult to address. This study shows that egg is required in the Drosophila ovary for trimethylation of histone H3 at its K9 residue. In females bearing an egg allele that deletes the SET domain, oogenesis arrests at early stages. This arrest is accompanied by reduced proliferation of somatic cells required for egg chamber formation, and by apoptosis in both germ and somatic cell populations. It is proposed that other closely related proteins may function similarly in gametogenesis in other species (Clough, 2007).

Female sterile (1) homeotic

Members of the Cas family of Src homology 3 (SH3)-domain-containing cytosolic signaling proteins are crucial regulators of actin cytoskeletal dynamics in non-neuronal cells; however, their neuronal functions are poorly understood. This study identified Drosophila p130CAS (DCas, CG1212, CAS; not to be confused with the Drosophila genes CAS/CSE1 segregation protein and castor), found that Cas proteins are highly expressed in neurons and showed that DCas is required for correct axon guidance during development. Functional analyses reveal that Cas specifies axon guidance by regulating the degree of fasciculation among axons. These guidance defects are similar to those observed in integrin mutants, and genetic analysis shows that integrins function together with Cas to facilitate axonal defasciculation. These results strongly support Cas proteins working together with integrins in vivo to direct axon guidance events (Huang, 2007).

Gustatory receptor 21a and Gustatory receptor 63a

Blood-feeding insects, including the malaria mosquito Anopheles gambiae, use highly specialized and sensitive olfactory systems to locate their hosts. This is accomplished by detecting and following plumes of volatile host emissions, which include carbon dioxide (CO₂). CO₂ is sensed by a population of olfactory sensory neurons in the maxillary palps of mosquitoes and in the antennae of Drosophila. The molecular identity of the chemosensory CO₂ receptor, however, remains unknown. This study reports that CO₂-responsive neurons in Drosophila co-express a pair of chemosensory receptors, Gr21a and Gr63a, at both larval and adult life stages. Mosquito homologues of Gr21a and Gr63a, GPRGR22 and GPRGR24 have been identified; these are co-expressed in A. gambiae maxillary palps. Gr21a and Gr63a together are sufficient for olfactory CO₂-chemosensation in Drosophila. Ectopic expression of Gr21a and Gr63a together confers CO₂ sensitivity on CO₂- insensitive olfactory neurons, but neither gustatory receptor alone has this function. Mutant flies lacking Gr63a lose both electrophysiological and behavioural responses to CO₂. Knowledge of the molecular identity of the insect olfactory CO₂ receptors may spur the development of novel mosquito control strategies designed to take advantage of this unique and critical olfactory pathway. This in turn could bolster the worldwide fight against malaria and other insect-borne diseases (Jones, 2007).

MICAL

The overall size and structure of a synaptic terminal is an important determinant of its function. In a large-scale mutagenesis screen, designed to identify Drosophila mutants with abnormally structured neuromuscular junctions (NMJs), mutations were discovered in Drosophila mical, a conserved gene encoding a multi-domain protein with a N-terminal monooxygenase domain. In mical mutants, synaptic boutons do not sprout normally over the muscle surface and tend to form clusters along synaptic branches and at nerve entry sites. Consistent with high expression of MICAL in somatic muscles, immunohistochemical stainings reveal that the subcellular localization and architecture of contractile muscle filaments are dramatically disturbed in mical mutants. Instead of being integrated into a regular sarcomeric pattern, actin and myosin filaments are disorganized and accumulate beneath the plasmamembrane. Whereas contractile elements are strongly deranged, the proposed organizer of sarcomeric structure, D-Titin, is much less affected. Transgenic expression of interfering RNA molecules demonstrates that MICAL is required in muscles for the higher order arrangement of myofilaments. Ultrastructural analysis confirms that myosin-rich thick filaments enter submembranous regions and interfere with synaptic development, indicating that the disorganized myofilaments may cause the synaptic growth phenotype. As a model, it is suggested that the filamentous network around synaptic boutons restrains the spreading of synaptic branches (Beuchle, 2007).

Little imaginal discs

The Myc oncoprotein is a potent inducer of cell growth, cell cycle progression, and apoptosis. While many direct Myc target genes have been identified, the molecular determinants of Myc's transcriptional specificity remain elusive. A genetic screen was carried out in Drosophila and the Trithorax group protein Little imaginal discs (Lid) was identified as a regulator of dMyc-induced cell growth. Lid was originally identified in intergenic noncomplementation with a mutation in ash1, a trithorax group gene (Gildea, 2000; full text of article). Lid binds to dMyc and is required for dMyc-induced expression of the growth regulatory gene Nop60B. The mammalian Lid orthologs, Rbp-2 (JARID1A) and Plu-1 (JARID1B), also bind to c-Myc, indicating that Lid-Myc function is conserved. Lid is a JmjC-dependent trimethyl H3K4 demethylase in vivo, and this enzymatic activity is negatively regulated by dMyc, which binds to Lid's JmjC domain. Because Myc binding is associated with high levels of trimethylated H3K4, it is proposed that the Lid-dMyc complex facilitates Myc binding to, or maintenance of, this chromatin context (Secombe, 2007). Identication of Lid as a histone H3 trimethyl-Lys4 demethylase has also been reported by Lee (2007) and Eissenberg (2007).

Odorant receptor 65a

Reproductive behavior in Drosophila has both stereotyped and plastic components that are driven by age- and sex-specific chemical cues. Males who unsuccessfully court virgin females subsequently avoid females that are of the same age as the trainer. In contrast, males trained with mature mated females associate volatile appetitive and aversive pheromonal cues and learn to suppress courtship of all females. This study shows that the volatile aversive pheromone that leads to generalized learning with mated females is (Z)-11-octadecenyl acetate (cis-vaccenyl acetate, cVA). cVA is a major component of the male cuticular hydrocarbon profile, but it is not found on virgin females. During copulation, cVA is transferred to the female in ejaculate along with sperm and peptides that decrease her sexual receptivity. When males sense cVA (either synthetic or from mated female or male extracts) in the context of female pheromone, they develop a generalized suppression of courtship. The effects of cVA on initial courtship of virgin females can be blocked by expression of tetanus toxin in Or65a, but not Or67d neurons, demonstrating that the aversive effects of this pheromone are mediated by a specific class of olfactory neuron. These findings suggest that transfer of cVA to females during mating may be part of the male's strategy to suppress reproduction by competing males (Ejima, 2007).

Or67d

Insects, like many other animals, use sex pheromones to coordinate their reproductive behaviours. Volatile pheromones are detected by odorant receptors expressed in olfactory receptor neurons (ORNs). Whereas fruit odours typically activate multiple ORN classes, pheromones are thought to act through single dedicated classes of ORN. This model predicts that activation of such an ORN class should be sufficient to trigger the appropriate behavioural response. This study shows that the Drosophila male-specific pheromone 11-cis-vaccenyl acetate (cVA) acts through the receptor Or67d to regulate both male and female mating behaviour. Mutant males that lack Or67d inappropriately court other males, whereas mutant females are less receptive to courting males. These data suggest that cVA has opposite effects in the two sexes: inhibiting mating behaviour in males but promoting mating behaviour in females. Replacing Or67d with moth pheromone receptors renders these ORNs sensitive to the corresponding moth pheromones. In such flies, moth pheromones elicit behavioural responses that mimic the normal response to cVA. Thus, activation of a single ORN class is both necessary and sufficient to mediate behavioural responses to the Drosophila sex pheromone cVA (Kurtovic, 2007).

p130CAS

More than a dozen trithorax group (trxG) proteins are involved in activation of Drosophila HOX genes. How they act coordinately to integrate signals from distantly located enhancers is not fully understood. The female sterile (1) homeotic [fs(1)h] gene is one of the trxG genes that is most critical for Ultrabithorax (Ubx) activation. One of the two double-bromodomain proteins encoded by fs(1)h acts as an essential factor in the Ubx proximal promoter. Three aspects are noted: (1) overexpression of the small isoform FSH-S, but not the larger one, can induce ectopic expression of HOX genes and cause body malformation; (3) FSH-S can stimulate Ubx promoter in cultured cells through a critical proximal region in a bromodomain-dependent manner; (3) purified FSH-S can bind specifically to a motif within this region that was previously known as the ZESTE site. The physiological relevance of FSH-S is ascertained using transgenic embryos containing a modified Ubx proximal promoter and chromatin immunoprecipitation. In addition, FSH-S is involved in phosphorylation of itself and other regulatory factors. It is suggested that FSH-S acts as a critical component of a regulatory circuitry mediating long-range effects of distant enhancers (Chang, 2007).

Perdido/Kon-tiki

Directed cell migration and target recognition are critical for the development of both the nervous and muscular systems. Molecular mechanisms that control these processes in the nervous system have been intensively studied, whereas those that act during muscle development are still largely uncharacterized. This study identified a transmembrane protein, Kon-tiki (Kon, FlyBase term Perdido), that mediates myotube target recognition in the Drosophila embryo. Kon is expressed in a specific subset of myotubes and is required autonomously for these myotubes to recognize their tendon cell targets and to establish a stable connection. Kon is enriched at myotube tips during targeting and signals through the intracellular adaptor Dgrip in a conserved molecular pathway. Forced overexpression of Kon stimulates muscle motility. It is proposed that Kon promotes directed myotube migration and transduces a target-derived signal that initiates the formation of a stable connection (Schnorrer, 2007).

Spt6

Spt6 was identified in Saccharomyces cerevisiae as a transcription elongation factor which interacts with histone H3 and H4 (Bortvin, 1996). Spt6 functions in chromatin disassembly. During transcription, Spt6 allows RNA Pol II to pass through the DNA template and re-establishes chromatin structure after RNA pol II passage (Adkins, 2006; Hartzog, 1998; Kaplan, 2003; Saunders, 2003; Swanson, 1992; Kok, 2007 and references therein). Specifically, in yeast the histone H3-H4 chaperone Spt6 mediates nucleosome reassembly onto promoters during transcriptional repression. In the absence of Spt6-mediated nucleosome reassembly transcription is sustained (Adkins, 2006). Mammalian Spt6 has been shown to bind phosphorylated serine of RNA polymerase II C-terminal domain through a primitive SH2 domain and recruit mRNA processing, surveillance, and export factors to responsive genes, thus providing a link between transcription and mRNA splicing and export (Yoh, 2007).

Squeeze

One of the most widely studied phenomena in the establishment of neuronal identity is the determination of neurosecretory phenotype, in which cell-type-specific combinatorial codes direct distinct neurotransmitter or neuropeptide selection. However, neuronal types from divergent lineages may adopt the same neurosecretory phenotype, and it is unclear whether different classes of neurons use different or similar components to regulate shared features of neuronal identity. This question was addressed by analyzing how differentiation of the Drosophila larval leucokinergic system, which is comprised of only four types of neurons, is regulated by factors known to affect expression of the FMRFamide neuropeptide. All leucokinergic cells express the transcription factor Squeeze (Sqz). However, based on the effect on Leucokinin (LK) expression of loss- and gain-of-function mutations, three types of LK regulation are described. In the brain LHLK (lateral horn leukokinin) cells, both Sqz and Apterous (Ap) are required for LK expression, but surprisingly, high levels of either Sqz or Ap alone are sufficient to restore LK expression in these neurons. In the suboesophageal SELK cells, Sqz, but not Ap, is required for LK expression. In the abdominal ABLK neurons, inhibition of retrograde axonal transport reduces LK expression, and although sqz is dispensable for LK expression in these cells, it can induce ectopic leucokinergic ABLK-like cells when over-expressed. Thus, Sqz appears to be a regulatory factor for neuropeptidergic identity common to all leucokinergic cells, whose function in different cell types is regulated by cell-specific factors (Herrero, 2007).

Suppressor of variegation 3-3

Histone-tail modifications play a fundamental role in the processes that establish chromatin structure and determine gene expression. One such modification, histone methylation, was considered irreversible until the recent discovery of histone demethylases. Lsd1 was the first histone demethylase to be identified (Shi, 2004). Lsd1 is highly conserved, from yeast to humans, but its function has primarily been studied through biochemical approaches. The mammalian ortholog has been shown to demethylate monomethyl- and dimethyl-K4 and -K9 residues of histone H3 (Shi, 2004; Metzger, 2005). This study, along with a second study by Rudolph (2007) describes the effects of Lsd1 [Su(var)3-3] mutation in Drosophila. The inactivation of dLsd1 strongly affects the global level of monomethyl- and dimethyl-H3-K4 methylation and results in elevated expression of a subset of genes. dLsd1 is not an essential gene, but animal viability is strongly reduced in mutant animals in a gender-specific manner. Interestingly, dLsd1 mutants are sterile and possess defects in ovary development, indicating that dLsd1 has tissue-specific functions. Mutant alleles of dLsd1 suppress positional-effect variegation, suggesting a disruption of the balance between euchromatin and heterochromatin. Taken together, these results show that dLsd1-mediated H3-K4 demethylation has a significant and specific role in Drosophila development (Di Stefano, 2007).

Unc-104

The morphological transition of growth cones to synaptic boutons characterizes synaptogenesis. This study isolated mutations in immaculate connections (imac; FlyBase name unc-104), encoding a member of the Kinesin-3 family. Whereas earlier studies in Drosophila has implicated Kinesin-1 in transporting synaptic vesicle precursors, this study found that Imac/Unc-104 is essential for this transport. An unexpected feature of imac mutants is the failure of synaptic boutons to form. Motor neurons lacking imac properly target to muscles but remain within target fields as thin processes, a structure that is distinct from either growth cones or mature terminals. Few active zones form at these endings. The arrest of synaptogenesis is not a secondary consequence of the absence of transmission. These data thus indicate that Imac transports components required for synaptic maturation and provide insight into presynaptic maturation as a process that can be differentiated from axon outgrowth and targeting (Pack-Chung, 2007).

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