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Through analysis of the Drosophila ionotropic receptors (IRs), a family of variant ionotropic glutamate receptors, we reveal that most IRs are expressed in peripheral neuron populations in diverse gustatory organs in larvae and adults. We characterise IR56d, which defines two anatomically-distinct neuron classes in the proboscis: one responds to carbonated solutions and fatty acids while the other represents a subset of sugar- and fatty acid-sensing cells. Mutational analysis indicates that IR56d, together with the broadly-expressed co-receptors IR25a and IR76b, is essential for physiological responses to carbonation and fatty acids, but not sugars. We further demonstrate that carbonation and fatty acids both promote IR56d-dependent attraction of flies, but through different behavioural outputs. Our work provides a toolkit for investigating taste functions of IRs, defines a subset of these receptors required for carbonation sensing, and illustrates how the gustatory system uses combinatorial expression of sensory molecules in distinct neurons to coordinate behaviour., Little is known about the role of variant ionotropic glutamate receptors (IRs) in insect taste. Here the authors characterise the expression pattern of IRs in the Drosophila gustatory system and highlight the role of one receptor, IR56d, in the detection of carbonation

The neurogenin (Ngn) transcription factors control early neurogenesis and neurite outgrowth in mammalian cortex. In contrast to their proneural activity, their function in neurite growth is poorly understood. Drosophila has a single predicted Ngn homolog, Tap, of unknown function. Here we show that Tap is not a proneural protein in Drosophila but is required for proper axonal growth and guidance of neurons of the mushroom body, a neuropile required for associative learning and memory. Genetic and expression analyses suggest that Tap inhibits excessive axonal growth by fine regulation of the levels of the Wnt signaling adaptor protein Dishevelled., info:eu-repo/semantics/published

0016-6731 (Print) Comparative Study Journal Article Research Support, Non-U.S. Gov't; Sex pheromones are intraspecific chemical signals that are crucial for mate attraction and discrimination. In Drosophila melanogaster, the predominant hydrocarbons on the cuticle of mature female and male flies are radically different and tend to stimulate or inhibit male courtship, respectively. This sexual difference depends largely upon the number of double bonds (one in males and two in females) added by desaturase enzymes. A mutation was caused by a PGal4 transposon inserted in the desat1 gene that codes for the desaturase crucial for setting these double bonds. Homozygous mutant flies produced 70-90% fewer sex pheromones than control flies, and the pheromonal difference between the sexes was almost abolished. A total of 134 excision alleles were induced by pulling out all or a part of the transposon. The pheromonal profile was generally rescued in excision alleles with a completely or largely removed transposon whereas it remained mutant in alleles with a larger piece of the transposon. Five desat1 transcripts were detected during larval-to-adult development. Their levels were precisely quantified in 24-hr-old adults, a critical period for the production of sex pheromones. Three transcripts significantly varied between control females and males; however, the predominant transcript showed no difference. In mutant flies, the predominant transcript was highly decreased with the two sexually dimorphic transcripts.These two transcripts were also absent in the sibling species D. simulans, which shows no sexually dimorphic hydrocarbons. We also induced a larval-lethal allele that lacked all transcripts and failed to complement the defective hydrocarbon phenotype of mutant alleles.

The destabilization of AU-rich element (ARE)-containing mRNAs mediated by proteins of the TIS11 family is conserved among eukaryotes including Drosophila. Previous studies have demonstrated that Tristetraprolin, a human protein of the TIS11 family, induces the degradation of ARE-containing mRNAs through a large variety of mechanisms including deadenylation, decapping, and P-body targeting. We have previously shown that the degradation of the mRNA encoding the antimicrobial peptide Cecropin A1 (CecA1) is controlled by the TIS11 protein (dTIS11) in Drosophila cells. In this study, we used CecA1 mRNA as a model to investigate the molecular mechanism of dTIS11-mediated mRNA decay. We observed that during the biphasic deadenylation and decay process of this mRNA, dTIS11 enhances deadenylation performed by the CCR4-CAF-NOT complex while the mRNA is still associated with ribosomes. Sequencing of mRNA degradation intermediates revealed that the complete deadenylation of the mRNA triggers its decapping and decay in both the 5'-3' and the 3'-5' directions. Contrary to the observations made for its mammalian homologs, overexpression of dTIS11 does not promote the localization of ARE-containing mRNAs in P-bodies but rather decreases the accumulation of CecA1 mRNA in these structures by enhancing the degradation process. Therefore, our results suggest that proteins of the TIS11 family may have acquired additional functions in the course of evolution from invertebrates to mammals., Journal Article, Research Support, Non-U.S. Gov't, SCOPUS: ar.j, info:eu-repo/semantics/published

Summary Perceptual decisions require the accumulation of sensory information to a response criterion. Most accounts of how the brain performs this process of temporal integration have focused on evolving patterns of spiking activity. We report that subthreshold changes in membrane voltage can represent accumulating evidence before a choice. αβ core Kenyon cells (αβc KCs) in the mushroom bodies of fruit flies integrate odor-evoked synaptic inputs to action potential threshold at timescales matching the speed of olfactory discrimination. The forkhead box P transcription factor (FoxP) sets neuronal integration and behavioral decision times by controlling the abundance of the voltage-gated potassium channel Shal (KV4) in αβc KC dendrites. αβc KCs thus tailor, through a particular constellation of biophysical properties, the generic process of synaptic integration to the demands of sequential sampling., Graphical Abstract, Highlights • Synaptic integration can implement a process of bounded evidence accumulation • FoxP acts in αβc Kenyon cells (KCs) to repress the voltage-gated potassium channel Shal • Shal regulates the ability of αβc KCs to summate synaptic inputs over time • Altering Shal currents in αβc KCs changes spike latencies and decision times, How is information integrated to allow perceptual decision-making? FoxP-expressing neurons in fruit flies accumulate sensory evidence as subthreshold voltage changes. The first spike signals that a decision.

1749-6632 (Electronic) 0077-8923; The evolution of communication is a fundamental biological problem. The genetic control of the signal and its reception must be tightly coadapted, especially in interindividual sexual communication. However, there is very little experimental evidence for tight genetic linkage connecting the emission of a signal and its reception. In Drosophila melanogaster, desat1 is the first known gene that simultaneously affects the emission and the perception of sex pheromones. Our experiments show that both aspects of pheromonal communication (the emission and the perception of sex pheromones) depend on distinct genetic control and may result from tissue-specific expression of different transcripts, all coding for the same desaturase. Therefore, and given the high conservation of its coding region, the pleiotropic activity of the desat1 gene may have arisen from an evolutionary process that shaped its regulatory regions.

extramacrochaetae (emc) functions during many developmental processes in Drosophila, such as sensory organ formation, sex determination, wing vein differentiation, regulation of eye photoreceptor differentiation, cell proliferation and development of the Malpighian tubules, trachea and muscles in the embryo. It encodes a Helix-Loop-Helix transcription factor that negatively regulates bHLH proteins. We show here that emc mRNA and protein are present throughout oogenesis in a dynamic expression pattern and that emc is involved in the regulation of chorionic appendage formation during late oogenesis. Expression of sense and antisense emc constructs as well as emc follicle cell clones leads to eggs with shorter, thicker dorsal appendages that are closer together at base than in the wild type. We demonstrate that emc lies downstream of fs(1)K10, gurken and EGFR in the Grk/EGFR signalling pathway and that it participates in controlling Broad-Complex expression at late stages of oogenesis.

0012-1606 (Print) Journal Article Research Support, Non-U.S. Gov't; Drosophila thoracic muscles are comprised of both direct flight muscles (DFMs) and indirect flight muscles (IFMs). The IFMs can be further subdivided into dorsolongitudinal muscles (DLMs) and dorsoventral muscles (DVMs). The correct patterning of each category of muscles requires the coordination of specific executive regulatory programs. DFM development requires key regulatory genes such as cut (ct) and apterous (ap), whereas IFM development requires vestigial (vg). Using a new vg(null) mutant, we report that a total absence of vg leads to DLM degeneration through an apoptotic process and to a total absence of DVMs in the adult. We show that vg and scalloped (sd), the only known VG transcriptional coactivator, are coexpressed during IFM development. Moreover, we observed an ectopic expression of ct and ap, two markers of DFM development, in developing IFMs of vg(null) pupae. In addition, in vg(null) adult flies, degenerating DLMs express twist (twi) ectopically. We provide evidence that ap ectopic expression can induce per se ectopic twi expression and muscle degeneration. All these data seem to indicate that, in the absence of vg, the IFM developmental program switches into the DFM developmental program. Moreover, we were able to rescue the muscle phenotype of vg(null) flies by using the activity of ap promoter to drive VG expression. Thus, vg appears to be a key regulatory gene of IFM development.

author can archive publisher's version/PDF (embargo 6 months) ; 1529-2401 (Electronic ISSN); International audience; To sense myriad environmental odors, animals have evolved multiple, large families of divergent olfactory receptors. How and why distinct receptor repertoires and their associated circuits are functionally and anatomically integrated is essentially unknown. We have addressed these questions through comprehensive comparative analysis of the Drosophila olfactory subsystems that express the ionotropic receptors (IRs) and odorant receptors (ORs). We identify ligands for most IR neuron classes, revealing their specificity for select amines and acids, which complements the broader tuning of ORs for esters and alcohols. IR and OR sensory neurons exhibit glomerular convergence in segregated, although interconnected, zones of the primary olfactory center, but these circuits are extensively interdigitated in higher brain regions. Consistently, behavioral responses to odors arise from an interplay between IR- and OR-dependent pathways. We integrate knowledge on the different phylogenetic and developmental properties of these receptors and circuits to propose models for the functional contributions and evolution of these distinct olfactory subsystems.

Background First identified in fruit flies with temperature-sensitive paralysis phenotypes, the Drosophila melanogaster TipE locus encodes four voltage-gated sodium (NaV) channel auxiliary subunits. This cluster of TipE-like genes on chromosome 3L, and a fifth family member on chromosome 3R, are important for the optional expression and functionality of the Para NaV channel but appear quite distinct from auxiliary subunits in vertebrates. Here, we exploited available arthropod genomic resources to trace the origin of TipE-like genes by mapping their evolutionary histories and examining their genomic architectures. Results We identified a remarkably conserved synteny block of TipE-like orthologues with well-maintained local gene arrangements from 21 insect species. Homologues in the water flea, Daphnia pulex, suggest an ancestral pancrustacean repertoire of four TipE-like genes; a subsequent gene duplication may have generated functional redundancy allowing gene losses in the silk moth and mosquitoes. Intronic nesting of the insect TipE gene cluster probably occurred following the divergence from crustaceans, but in the flour beetle and silk moth genomes the clusters apparently escaped from nesting. Across Pancrustacea, TipE gene family members have experienced intronic nesting, escape from nesting, retrotransposition, translocation, and gene loss events while generally maintaining their local gene neighbourhoods. D. melanogaster TipE-like genes exhibit coordinated spatial and temporal regulation of expression distinct from their host gene but well-correlated with their regulatory target, the Para NaV channel, suggesting that functional constraints may preserve the TipE gene cluster. We identified homology between TipE-like NaV channel regulators and vertebrate Slo-beta auxiliary subunits of big-conductance calcium-activated potassium (BKCa) channels, which suggests that ion channel regulatory partners have evolved distinct lineage-specific characteristics. Conclusions TipE-like genes form a remarkably conserved genomic cluster across all examined insect genomes. This study reveals likely structural and functional constraints on the genomic evolution of insect TipE gene family members maintained in synteny over hundreds of millions of years of evolution. The likely common origin of these NaV channel regulators with BKCa auxiliary subunits highlights the evolutionary plasticity of ion channel regulatory mechanisms.

International audience; How do evolved genetic changes alter the nervous system to produce different patterns of behavior? We address this question using Drosophila male courtship behavior, which is innate, stereotyped, and evolves rapidly between species. D. melanogaster male courtship requires the male-specific isoforms of two transcription factors, fruitless and doublesex. These genes underlie genetic switches between female and male behaviors, making them excellent candidate genes for courtship behavior evolution. We tested their role in courtship evolution by transferring the entire locus for each gene from divergent species to D. melanogaster. We found that despite differences in Fru+ and Dsx+ cell numbers in wild-type species, cross-species transgenes rescued D. melanogaster courtship behavior and no species-specific behaviors were conferred. Therefore, fru and dsx are not a significant source of evolutionary variation in courtship behavior.