Interspecific Comparison of the Transformer Gene of Drosophila Reveals an Unusually High Degree of Evolutionary Divergence

The transformer (tra) gene of Drosophila melanogaster occupies an intermediate position in the regulatory pathway controlling all aspects of somatic sexual differentiation. The female-specific expression of this gene's function is regulated by the Sex lethal (Sxl) gene, through a mechanism involving sex-specific alternative splicing of tra pre-mRNA. The tra gene encodes a protein that is thought to act in conjunction with the transformer-2 (tra-2) gene product to control the sex-specific processing of doublesex (dsx) pre-mRNA. The bifunctional dsx gene carries out opposite functions in the two sexes, repressing female differentiation in males and repressing male differentiation in females. Here we report the results from an evolutionary approach to investigate tra regulation and function, by isolating the tra-homologous genes from selected Drosophila species, and then using the interspecific DNA sequence comparisons to help identify regions of functional significance. The tra-homologous genes from two Sophophoran subgenus species, Drosophila simulans and Drosophila erecta, and two Drosophila subgenus species, Drosophila hydei and Drosophila virilis, were cloned, sequenced and compared to the D. melanogaster tra gene. This comparison reveals an unusually high degree of evolutionary divergence among the tra coding sequences. These studies also highlight a highly conserved sequence within intron one that probably defines a cis-acting regulator of the sex-specific alternative splicing event.     

Genetics of sexual behaviour in Drosophila

The analysis of genetics of behaviour within and between species provides important clues about the forces shaping the evolution of behavioural genes. In Drosophila, a number of key processes such as emergence from the pupal case, locomotor activity, feeding, olfaction and aspects of mating behaviour are under circadian regulation. Genes controlling sexual behaviour are likely to control species specific differences in courtship that are involved in reproductive isolation of closely related species. Courtship in Drosophila is characterized by a series of stereotyped behaviours that lead to copulation and more than 30 genes have been identified through mutations that affect one or more of these elements. Although curiosity about behavioural differences between the sexes undoubtedly predates recorded history, little efforts have been made to uncover the molecular basis of male and female courtship. The brain and nervous system functions that underlie sex-specific behaviour are of obvious importance to all animals including humans. To understand behaviour related to sex it is important to distinguish those aspects that are controlled genetically. The isolation and analysis of Drosophila mutants with altered sexual orientation lead to the identification of novel branches in the sex-determination cascade, which govern the sexually dimorphic development of the nervous system.     

Genetic identification of neurons controlling a sexually dimorphic behaviour

In the fruit fly Drosophila melanogaster, locomotor activity is sexually dimorphic: female flies constantly modulate their activity pattern whereas males show a steadier, stereotyped walking pace [1]. Here, we mapped the area of the brain controlling this behavioural dimorphism. Adult male Drosophila expressing a dominant feminising transgene in a small cluster of neurons in the pars intercerebralis exhibited a female-like pattern of locomotor activity. Genetic ablation of these neurons prevented the feminisation of the locomotor activity of transgenic males. The results suggest that this cluster of neurons modulates sex-specific activity, but is not involved in initiating fly locomotion. Nor does it control male courtship behaviour, because feminisation of courtship was not correlated with the feminisation of locomotor activity.     

Sex differences in lizard escape decisions vary with latitude,but not sexual dimorphism

Sexual selection is a powerful evolutionary mechanism that has shaped the physiology, behaviour and morphology of the sexes to the extent that it can reduce viability while promoting traits that enhance reproductive success. Predation is one of the underlying mechanisms accounting for viability costs of sexual displays. Therefore, we should expect that individuals of the two sexes adjust their anti-predator behaviour in response to changes in predation risk. We conducted a meta-analysis of 28 studies (42 species) of sex differences in risk-taking behaviour in lizards and tested whether these differences could be explained by sexual dichromatism, by sexual size dimorphism or by latitude. Latitude was the best predictor of the interspecific heterogeneity in sex-specific behaviour. Males did not change their escape behaviour with latitude, whereas females had increasingly reduced wariness at higher latitudes. We hypothesize that this sex difference in risk-taking behaviour is linked to sex-specific environmental constraints that more strongly affect the reproductive effort of females than males. This novel latitudinal effect on sex-specific anti-predator behaviour has important implications for responses to climate change and for the relative roles of natural and sexual selection in different species.     

Functional conservation of the<Emphasis Type="Italic"> Sex-lethal</Emphasis> sex determining promoter,<Emphasis Type="Italic"> Sxl-Pe</Emphasis>, in<Emphasis Type="Italic"> Drosophila virilis</Emphasis>

The primary sex determination signal in Drosophila melanogaster, the ratio of X chromosomes to autosomes, sets the activity state of the switch gene, Sex-lethal ( Sxl), by regulating the establishment promoter, m-Sxl-Pe. We have identified and characterized the establishment promoter, v-Sxl-Pe, of the distantly related species Drosophila virilis. Like melanogaster, the virilis Sxl-Pe is organized into four sub-domains: the Sxl-Pe mRNA leader and exon E1 of Sxl protein, the core promoter, the sex-specific element and the augmentation element. The core promoter and sex-specific element of v-Sxl-Pe show considerable sequence similarity to m-Sxl-Pe and contain target sites for components of the X/A signaling system. While the augmentation element of v-Sxl-Pe also has sequence motifs that could function as target sites for the X/A signaling system, it shows little similarity to the melanogaster augmentation element. Functional studies reveal that v-Sxl-Pe drives sex-specific expression in D. melanogaster embryos and that the activity of the virilis promoter is controlled by known components of the melanogaster X/A counting system. Although v-Sxl-Pe responds appropriately to the melanogaster sex determination signal, it is less active than Sxl-Pe from melanogaster. Unexpectedly, the reduced activity is due to differences in the activity of the conserved core promoter, while the non-conserved augmentation element functions effectively. These findings suggest that low-affinity target sites for the X/A counting system are critical for the functioning of Sxl-Pe.     

Distinct regulatory programs establish widespread sex-specific alternative splicing in Drosophila melanogaster

In Drosophila melanogaster, female-specific expression of Sex-lethal (SXL) and Transformer (TRA) proteins controls sex-specific alternative splicing and/or translation of a handful of regulatory genes responsible for sexual differentiation and behavior. Recent findings in 2009 by Telonis-Scott et al. document widespread sex-biased alternative splicing in fruitflies, including instances of tissue-restricted sex-specific splicing. Here we report results arguing that some of these novel sex-specific splicing events are regulated by mechanisms distinct from those established by female-specific expression of SXL and TRA. Bioinformatic analysis of SXL/TRA binding sites, experimental analysis of sex-specific splicing in S2 and Kc cells lines and of the effects of SXL knockdown in Kc cells indicate that SXL-dependent and SXL-independent regulatory mechanisms coexist within the same cell. Additional determinants of sex-specific splicing can be provided by sex-specific differences in the expression of RNA binding proteins, including Hrp40/Squid. We report that sex-specific alternative splicing of the gene hrp40/squid leads to sex-specific differences in the levels of this hnRNP protein. The significant overlap between sex-regulated alternative splicing changes and those induced by knockdown of hrp40/squid and the presence of related sequence motifs enriched near subsets of Hrp40/Squid-regulated and sex-regulated splice sites indicate that this protein contributes to sex-specific splicing regulation. A significant fraction of sex-specific splicing differences are absent in germline-less tudor mutant flies. Intriguingly, these include alternative splicing events that are differentially spliced in tissues distant from the germline. Collectively, our results reveal that distinct genetic programs control widespread sex-specific splicing in Drosophila melanogaster.     

果蝇求偶行为的影响因素及其分子基础

果蝇Drosophila melanogaster Meigen是进行行为遗传学研究的极好材料。果蝇的雄性求偶行为已经被作为行为遗传学研究的模式。文章简要介绍近年来在遗传和分子水平上对果蝇性信息素和求偶行为的研究进展,尤其是突变体在果蝇行为遗传学研究中的应用。通过对果蝇求偶行为的分析,分别介绍果蝇的性信息素及视觉、听觉、嗅觉和味觉相关基因在果蝇求偶和交配行为过程中的作用。     

Drosophila female courtship and mating behaviors: sensory signals, genes, neural structures and evolution

Interest in Drosophila courtship behavior has a long-standing tradition, starting with the works by Sturtevant in 1915, and by Bastock and Manning in the 50s. The neural and genetic base of Drosophila melanogaster courtship behavior has made big strides in recent years, but the studies on males far outnumber those on females. Recent technical developments have made it possible to begin to unravel the biological substrates underlying the complexity of Drosophila female sexual behavior and its decisive effect on mating success. The present review focus more on the female side and summarizes the sensory signals that the male sends, using multiple channels, and which neural circuits and genes are mediating sex-specific behavioral responses.     

Analysis of a null mutation in the Drosophila splicing regulator Tra2 suggests its function is restricted to sexual differentiation

Tra2 is a regulator of pre-mRNA splicing and a key component of the Drosophila somatic sex determination pathway. Functional orthologs of this protein are thought to perform nonsex-specific functions essential for viability in both vertebrates and nematodes. Although Drosophila Tra2 is expressed throughout the soma of both sexes, studies on it have focused only on the sex-specific phenotypes of known viable alleles. Here we show that that widely used tra2 mutant alleles have residual activity and are not suitable for evaluating its effect on viability. To test whether Tra2 has an essential role in development, we generated a transposon-induced deletion in critical coding sequences. We find that tra2 deletion adults can survive as well as their heterozygous siblings. Thus, in contrast to other organisms, Tra2 is not required in Drosophila for general viability under laboratory conditions.     

The Orthologue of the Fruitfly Sex Behaviour Gene Fruitless in the Mosquito Aedes aegypti: Evolution of Genomic Organisation and Alternative Splicing

In Drosophila melanogaster the doublesex (dsx) and fruitless (fru) regulatory genes act at the bottom of the somatic sex determination pathway. Both are regulated via alternative splicing by an upstream female-specific TRA/TRA-2 complex, recognizing a common cis element. dsx controls somatic sexual differentiation of non-neural as well as of neural tissues. fru, on the other hand, expresses male-specific functions only in neural system where it is required to built the neural circuits underlying proper courtship behaviour. In the mosquito Aedes aegypti sex determination is different from Drosophila. The key male determiner M, which is located on one of a pair of homomorphic sex chromosomes, controls sex-specific splicing of the mosquito dsx orthologue. In this study we report the genomic organization and expression of the fru homologue in Ae. aegypti (Aeafru). We found that it is sex-specifically spliced suggesting that it is also under the control of the sex determination pathway. Comparative analyses between the Aeafru and Anopheles gambiae fru (Angfru) genomic loci revealed partial conservation of exon organization and extensive divergence of intron lengths. We find that Aeadsx and Aeafru share novel cis splicing regulatory elements conserved in the alternatively spliced regions. We propose that in Aedes aegypti sex-specific splicing of dsx and fru is most likely under the control of splicing regulatory factors which are different from TRA and TRA-2 found in other dipteran insects and discuss the potential use of fru and dsx for developing new genetic strategies in vector control.     

Steroid Signaling within Drosophila Ovarian Epithelial Cells Sex-Specifically Modulates Early Germ Cell Development and Meiotic Entry

Drosophila adult females but not males contain high levels of the steroid hormone ecdysone, however, the roles played by steroid signaling during Drosophila gametogenesis remain poorly understood. Drosophila germ cells in both sexes initially follow a similar pathway. After germline stem cells are established, their daughters form interconnected cysts surrounded by somatic escort (female) or cyst (male) cells and enter meiosis. Subsequently, female cysts acquire a new covering of somatic cells to form follicles. Knocking down expression of the heterodimeric ecdysteroid receptor (EcR/Usp) or the E75 early response gene in escort cells disrupts 16-cell cyst production, meiotic entry and follicle formation. Escort cells lose their squamous morphology and unsheath germ cells. By contrast, disrupting ecdysone signaling in males does not perturb cyst development or ensheathment. Thus, sex-specific steroid signaling is essential for female germ cell development at the time male and female pathways diverge. Our results suggest that steroid signaling plays an important sex-specific role in early germ cell development in Drosophila, a strategy that may be conserved in mammals.     

The regulation of <Emphasis Type="Italic">yp3</Emphasis> expression in the <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> fat body

The regulation of the Drosophila melanogaster yolk protein genes 1 and 2 have been well characterised. Cis-acting DNA elements and trans-acting factors regulating ovarian fat body and sex-specific expression have been identified. In this paper we have analysed the regulation of yolk protein 3, which is separated from the other two genes on the X-chromosome. We have separated sex-specific control from fat body control in some constructs in transgenic flies. We propose that the organisation of the regulatory elements in yp3 differs from yp1 and yp2 for control of fat body expression and that it closely resembles the regulation of a reporter gene using Musca and Calliphora yp promoter enhancer sequences in transgenic Drosophila.     

<Emphasis Type="Italic">fruitless</Emphasis> alternative splicing and sex behaviour in insects: an ancient and unforgettable love story?

Courtship behaviours are common features of animal species that reproduce sexually. Typically, males are involved in courting females. Insects display an astonishing variety of courtship strategies primarily based on innate stereotyped responses to various external stimuli. In Drosophila melanogaster, male courtship requires proteins encoded by the fruitless (fru) gene that are produced in different sex-specific isoforms via alternative splicing. Drosophila mutant flies with loss-of-function alleles of the fru gene exhibit blocked male courtship behaviour. However, various individual steps in the courtship ritual are disrupted in fly strains carrying different fru alleles. These findings suggest that fru is required for specific steps in courtship. In distantly related insect species, various fru paralogues were isolated, which shows conservation of sex-specific alternative splicing and protein expression in neural tissues and suggests an evolutionary functional conservation of fru in the control of male-specific-courtship behaviour. In this review, we report the seminal findings regarding the fru gene, its splicing regulation and evolution in insects.     

Molecular neurogenetics of sexual differentiation and behaviour

Sex and death. Two things that come once in a lifetime. Only after death you're not nauseous. - Woody Allen 'Sleeper'. The brain and nervous system functions that underlie sex-specific behaviour are of obvious importance to all animals, including humans. To understand behaviour related to sex, it is important to distinguish those aspects that are controlled genetically. Much of the recent progress in studies of the molecular neurogenetics of sexual differentiation and behaviour has come from the use of genetically tractable organisms (i.e. fruitflies and nematode worms) that exhibit a full range of sexually dimorphic phenotypes.     

Sexual differentiation of gonadotrophin secretion, sexual orientation and gender role behavior

The positive estrogen feedback was found to be a relatively sex-specific reaction of the hypothalamo-hypophyseal system in rats as well as in human beings. It is dependent--most of all--on the estrogen convertible androgen level during sexual brain differentiation, but also on an estrogen priming effect in adulthood. The lower the estrogen convertible androgen or primary estrogen level during brain differentiation, the higher is the evocability of a positive estrogen action on LH secretion in later life. In clinical studies, we were able to induce a positive estrogen feedback on LH secretion in most intact homosexual men in clear-cut contrast to intact hetero- or bisexual men. These findings were strongly confirmed by Gladue and associates. In addition, the evocability of a positive estrogen feedback was also demonstrable in most homosexual male-to-female transsexuals in significant contrast to hetero- or bisexual male-to-female transsexuals. These findings suggest that homosexual males possess, at least in part, a predominantly female-differentiated brain, which may be caused by a low estrogen convertible androgen level during brain organization. Recently, the following relations were found between sex hormone levels during brain differentiation and sex-specific responses in adulthood: (1) estrogens--which are mostly converted, however, from androgens--are responsible for the sex-specific organization of gonadotrophin secretion and hence the evocability of a positive estrogen feedback in later life; (2) estrogens and androgens, occurring during brain differentiation, predetermine synergistically sexual orientation and (3) androgens--without conversion to estrogens--are responsible for the sex-specific organization of gender role behaviour in later life. Furthermore, the organization periods for sex-specific gonadotrophin secretion, sexual orientation and gender role behaviour are not identical but overlapping. Thus, combinations as well as dissociations between deviations of the neuroendocrine organization of sex-specific gonadotrophin secretion, sexual orientation and gender role behaviour are conceivable. Most recently, female-type sexual orientation could be converted to male-type sexual orientation in adult rats by administration of the dopamine agonist and serotonin antagonist lisuride.     

Sex differences in motor unit behaviour: A review

The lack of systematic investigations on sex-related differences in motor unit behaviour poses a challenge in understanding and optimizing health and performance in males and females. Limited investigations revealed that sex differences in motor unit behaviour might be present in human muscles. This review summarizes the current knowledge on sex differences in motor unit behaviour and potential factors that may contribute to these differences. We show significant under-representation of female participants in motor unit studies and a limited number of studies investigating sex differences in motor unit behaviour. We place the current insights within the context of methodological limitations and outline several recommendations and future directions to improve female representation in this research area. We conclude that there is an urgent need to gather more data in females and investigate sex differences in motor unit behaviour. The knowledge gained could be used to develop sex-specific approaches to improve neuromuscular performance and rehabilitation.