fruitless splicing specifies male courtship behavior in Drosophila

All animals exhibit innate behaviors that are specified during their development. Drosophila melanogaster males (but not females) perform an elaborate and innate courtship ritual directed toward females (but not males). Male courtship requires products of the fruitless (fru) gene, which is spliced differently in males and females. We have generated alleles of fru that are constitutively spliced in either the male or the female mode. We show that male splicing is essential for male courtship behavior and sexual orientation. More importantly, male splicing is also sufficient to generate male behavior in otherwise normal females. These females direct their courtship toward other females (or males engineered to produce female pheromones). The splicing of a single neuronal gene thus specifies essentially all aspects of a complex innate behavior.     

Drosophila retained/dead ringer is necessary for neuronal pathfinding, female receptivity and repression of fruitless independent male courtship behaviors

Mutations in the Drosophila retained/dead ringer (retn) gene lead to female behavioral defects and alter a limited set of neurons in the CNS. retn is implicated as a major repressor of male courtship behavior in the absence of the fruitless (fru) male protein. retn females show fru-independent male-like courtship of males and females, and are highly resistant to courtship by males. Males mutant for retn court with normal parameters, although feminization of retn cells in males induces bisexuality. Alternatively spliced RNAs appear in the larval and pupal CNS, but none shows sex specificity. Post-embryonically, retn RNAs are expressed in a limited set of neurons in the CNS and eyes. Neural defects of retn mutant cells include mushroom body beta-lobe fusion and pathfinding errors by photoreceptor and subesophageal neurons. We posit that some of these retn-expressing cells function to repress a male behavioral pathway activated by fruM.     

Excitatory and inhibitory switches for courtship in the brain of Drosophila melanogaster

BACKGROUND: Courtship is the best-studied behavior in Drosophila melanogaster, and work on its anatomical basis has concentrated mainly on the functional identification of sexually dimorphic sites in the brain. Much less is known of the more expansive, nondimorphic, but nonetheless essential, neural elements subserving male courtship behavior. RESULTS: Sites in the CNS mediating initiation and early steps of male courtship in Drosophila melanogaster were identified by analyzing the behavior of mosaic flies expressing transgenes designed either to suppress neurotransmission or enhance neuronal excitability. Suppression of neurotransmission was accomplished by means of the dominantly acting, temperature-sensitive dynamin mutation shibire(ts1), whereas enhanced neuronal excitability was produced by means of a novel, dominantly acting, truncated eag potassium channel. By using a new, landmark-based procedure for aligning diverse expression patterns among the various mosaic strains, a comparison of courtship performance and affected brain sites in strains expressing the transgenes identified a cluster of cells in the posterior lateral protocerebrum that exerts reciprocal effects on the initiation of courtship, suppressing it when they are inactivated and enhancing it when they are hyperactivated, indicative of cells that normally play an excitatory, triggering role. A separate group of nearby cells, slightly more anterior in the lateral protocerebrum, was found to inhibit courtship when its activity is enhanced, indicative of an inhibitory role in courtship. CONCLUSIONS: A cluster of cells, some excitatory and some inhibitory, in the lateral protocerebrum regulates courtship initiation in Drosophila. These cells are likely to be an integration center for the multiple sensory inputs that trigger male courtship.     

A gene necessary for late sperm function in Drosophila melanogaster.

A male-sterile mutant, ms(1)7, of Drosophila melanogaster is defective in post-ejaculatory sperm function. The mutant gene is located at one of at least five male fertility loci in 18F through section 20 of the polytene X-chromosome. It is proposed that the ms(1)7+ gene product modifies a component of the sperm head. A nearby gene may be functionally related to ms(1)7+.     

Two distinct genomic regions, harbouring the period and fruitless genes, affect male courtship song in Drosophila montana

Acoustic signals often have a significant role in pair formation and in species recognition. Determining the genetic basis of signal divergence will help to understand signal evolution by sexual selection and its role in the speciation process. An earlier study investigated quantitative trait locus for male courtship song carrier frequency (FRE) in Drosophila montana using microsatellite markers. We refined this study by adding to the linkage map markers for 10 candidate genes known to affect song production in Drosophila melanogaster. We also extended the analyses to additional song characters (pulse train length (PTL), pulse number (PN), interpulse interval, pulse length (PL) and cycle number (CN)). Our results indicate that loci in two different regions of the genome control distinct features of the courtship song. Pulse train traits (PTL and PN) mapped to the X chromosome, showing significant linkage with the period gene. In contrast, characters related to song pulse properties (PL, CN and carrier FRE) mapped to the region of chromosome 2 near the candidate gene fruitless, identifying these genes as suitable loci for further investigations. In previous studies, the pulse train traits have been found to vary substantially between Drosophila species, and so are potential species recognition signals, while the pulse traits may be more important in intra-specific mate choice.     

A gene involved in the food preferences of larval Drosophila melanogaster

To examine the mechanism by which insects change their food preferences, a simple method was developed to measure their preferences. By using this method, we demonstrated preference of Drosophila melanogaster larvae of the yw control strain for a food based on soybeans over one based on cornmeal. We then screened for mutant strains with food preferences clearly different from the control yw strain, using the Gene Search collection of P-element insertions (GS strains). Among 380 GS strains screened using an assay plate-containing soybean and corn tastants, we identified one mutant, GS1189 that did not show any preference for either of the foods. Further behavioral assays indicated that the GS1189 larvae could have impaired olfactory and gustatory systems. The fact that the CG33071 gene expression was inactivated by the P-element insertion in the GS1189 strain, and that reversion of this gene completely recovered the normal food preference, indicates that this gene contributes to the control of food preferences in Drosophila larvae.     

Cycles in the courtship song of male Drosophila melanogaster have not been detected

Cyclical short-term fluctuations in the mean inter-pulse intervals of Drosophila courtship song have been previously described. The failure to repeat these results is reported and it is shown that if such cycles do indeed exist, the methods of analysis employed have been inappropriate and, furthermore, that the sample sizes have been inadequate to demonstrate the phenomenon.     

Deletion of the Drosophila neuronal gene found in neurons disrupts brain anatomy and male courtship

The fne (found‐in‐neurons) locus encodes one of the three paralogs of the ELAV gene family of Drosophila melanogaster. Members of this family are found throughout metazoans and encode RNA‐binding proteins with primarily neuronal localization, but with remarkably diverse functions given their high level of amino acid sequence conservation. The first identified member of the family, elav of Drosophila is a vital gene. Mutations in the second Drosophila elav paralog, rbp9, are viable but female sterile. No alleles of fne were previously available. FNE protein is normally present in the cytoplasm of all neurons throughout development. Here we describe the generation and characterization of fne^null mutations by homologous recombination. In contrast to elav and similar to rbp9, fne^null mutants are viable, but exhibit a specific and fully penetrant fusion of the β‐lobes in their mushroom bodies (MB), a paired neuropil of the central brain involved in a variety of complex behaviors. Mutant males have reduced courtship indices, but normal short‐ and long‐term courtship memory. Our data show that fne has specific functions which are non‐overlapping with the other two family members, namely in courtship behavior and in the development of the adult MB. The data further show that courtship memory does not require intact β‐lobes in the MB.     

Turning males on: activation of male courtship behavior in Drosophila melanogaster

The innate sexual behaviors of Drosophila melanogaster males are an attractive system for elucidating how complex behavior patterns are generated. The potential for male sexual behavior in D. melanogaster is specified by the fruitless (fru) and doublesex (dsx) sex regulatory genes. We used the temperature-sensitive activator dTRPA1 to probe the roles of fru(M)- and dsx-expressing neurons in male courtship behaviors. Almost all steps of courtship, from courtship song to ejaculation, can be induced at very high levels through activation of either all fru(M) or all dsx neurons in solitary males. Detailed characterizations reveal different roles for fru(M) and dsx in male courtship. Surprisingly, the system for mate discrimination still works well when all dsx neurons are activated, but is impaired when all fru(M) neurons are activated. Most strikingly, we provide evidence for a fru(M)-independent courtship pathway that is primarily vision dependent.     

Regulation of larval cuticle protein gene expression in Drosophila melanogaster

Genes that encode 3rd instar larval cuticle proteins (LCP's) of Drosophila melanogaster are located in at least two chromosomal sites. The genes encoding four of the five predominant LCP's are located in a cluster at the chromosomal region 44D. They are organized in pairs that are transcribed divergently, and expressed with different timing during the third larval instar. Towards understanding the basis of gene regulation within the 44D cluster, we have analyzed genetic variants, including the 2-3 variant, which has an insertion of a copia-like transposable element, H.M.S. Beagle, within the 44D cluster. The Beagle element appears to inactivate the LCP-3 gene by inserting into its TATA box, but also may cause the precocious expression of two other LCP genes, LCP-1 and LCP-f2, in the cluster. The long terminal repeat (LTR) of the Beagle element apparently contains a sequence, perhaps an enhancer-like element, which causes altered expression of these genes. We have also investigated the cis-regulatory elements involved in expression of the LCP-2 gene in wild-type larvae. We have identified two upstream regions that may contain separate cis-regulatory elements. The region between -252 bp and -515 bp may be essential for any expression of LCP-2. Additionally, the region between -515 bp and -795 bp appears to be required for the normal level of expression of the LCP-2 gene.     

Physiological factors in the courtship processing of Drosophila melanogaster

The sexual receptivity of young virgin Drosophila melanogaster females develops between 24 and 48 hr from eclosion. Measurement of this process suggests that percentage receptivity (reflecting ‘switch-on’) and courtship duration (reflecting ‘courtship processing’) may not be controlled by entirely different processes. A decline in courtship duration was found to accompany the swtich-on of receptivity, suggesting that the settings in the courtship processing system are under the control of the same developmental process.Once a female has become sexually mature her courtship processing system is set to require certain quantities of courtship before acceptance occurs. This setting is stable, at least while the female is still virgin, and is correlated with a fundamental variable in the reproductive biology of the female, her fecundity.     

Effects of female behavior on wing display and courtship of male Drosophila simulans and Drosophila melanogaster

Corrolations between female rejection behaviors and male wing display were calculated for both Drosophila simulans and Drosophila melanogaster intraspicific pair-matings. No significant correlations were found for D. melanogaster, but in D. simulans flicking by the female appeared to be associated with a shift in male wing display pattern resulting in higher levels of vibration. Flicking did not appear to discourage courtship by males in either species.     

Functional coupling of acoustic and chemical signals in the courtship behaviour of the male Drosophila melanogaster

During courtship, the male Drosophila melanogaster sends signals to the female through two major sensory channels: chemical and acoustic. These signals are involved in the stimulation of the female to accept copulation. In order to determine the respective importance in the courtship of these signals, their production was controlled using genetical and surgical techniques. Males deprived of the ability to emit both signals are unable to mate, demonstrating that other (e.g. visual or tactile) signals are not sufficient to stimulate the female. If either acoustic or chemical signals are lacking, the courtship success is strongly reduced, the lack of the former having significantly more drastic effects. However, the accelerated matings of males observed with males bearing wild-type hydrocarbons compared with defective ones, whichever the modality of acoustic performance (wing vibration or playback), strongly support the role of cuticular compounds to stimulate females. We can conclude that among the possible factors involved in communication during courtship, acoustic and chemical signals may act in a synergistic way and not separately in D. melanogaster.     

Cell-specific immuno-probes for the brain of normal and mutant Drosophila melanogaster

Summary We have screened antibodies for immunocytochemical staining in the optic lobes of the brain of Drosophila melanogaster. Seven polyclonal antisera and five monoclonal antibodies are described that selectively and reproducibly stain individual cells and/or produce characteristic staining patterns in the neuropile. Such antisera are useful for the cellular characterization of molecular and structural brain defects in visual mutants. In the wildtype visual system we can at present separately stain the following: the entire complement of columnar T 1 neurons; a small set of presumptive serotonergic neurons; some 3000 cells that contain and synthesize -amino butyric acid (GABA); and three groups of cells that bind antibodies to Ca²⁺-binding proteins. In addition, small groups of hitherto unknown tangential cells that send fine arborizations into specific strata of the medulla, and two patterns of characteristic layers in the visual neuropile have been identified by use of monoclonal antibodies generated following immunization of mice with homogenates of the brain of Drosophila melanogaster.