The sex determination gene doublesex regulates expression and secretion of the basement membrane protein Collagen IV

Tissue-specific metabolomic signatures for a doublesex model of reduced sexual dimorphism

Sex has a major effect on the metabolome. However, we do not yet understand the degree to which these quantitative sex differences in metabolism are associated with anatomical dimorphism and modulated by sex-specific tissues. In the fruit fly, Drosophila melanogaster, knocking out the doublesex (dsx) gene gives rise to adults with intermediate sex characteristics. Here we sought to determine the degree to which this key node in sexual development leads to sex differences in the fly metabolome. We measured 91 metabolites across head, thorax and abdomen in Drosophila, comparing the differences between distinctly sex-dimorphic flies with those of reduced sexual dimorphism: dsx null flies. Notably, in the reduced dimorphism flies, we observed a sex difference in only 1 of 91 metabolites, kynurenate, whereas 51% of metabolites (46/91) were significantly different between wildtype XX and XY flies in at least one tissue, suggesting that dsx plays a major role in sex differences in fly metabolism. Kynurenate was consistently higher in XX flies in both the presence and absence of functioning dsx. We observed tissue-specific consequences of knocking out dsx. Metabolites affected by sex were significantly enriched in branched chain amino acid metabolism and the mTOR pathway. This highlights the importance of considering variation in genes that cause anatomical sexual dimorphism when analyzing sex differences in metabolic profiles and interpreting their biological significance.

Finishing the egg

Gamete development is a fundamental process that is highly conserved from early eukaryotes to mammals. As germ cells develop, they must coordinate a dynamic series of cellular processes that support growth, cell specification, patterning, the loading of maternal factors (RNAs, proteins, and nutrients), differentiation of structures to enable fertilization and ensure embryonic survival, and other processes that make a functional oocyte. To achieve these goals, germ cells integrate a complex milieu of environmental and developmental signals to produce fertilizable eggs. Over the past 50 years, Drosophila oogenesis has risen to the forefront as a system to interrogate the sophisticated mechanisms that drive oocyte development. Studies in Drosophila have defined mechanisms in germ cells that control meiosis, protect genome integrity, facilitate mRNA trafficking, and support the maternal loading of nutrients. Work in this system has provided key insights into the mechanisms that establish egg chamber polarity and patterning as well as the mechanisms that drive ovulation and egg activation. Using the power of Drosophila genetics, the field has begun to define the molecular mechanisms that coordinate environmental stresses and nutrient availability with oocyte development. Importantly, the majority of these reproductive mechanisms are highly conserved throughout evolution, and many play critical roles in the development of somatic tissues as well. In this chapter, we summarize the recent progress in several key areas that impact egg chamber development and ovulation. First, we discuss the mechanisms that drive nutrient storage and trafficking during oocyte maturation and vitellogenesis. Second, we examine the processes that regulate follicle cell patterning and how that patterning impacts the construction of the egg shell and the establishment of embryonic polarity. Finally, we examine regulatory factors that control ovulation, egg activation, and successful fertilization.

A male-specific doublesex isoform reveals an evolutionary pathway of sexual development via distinct alternative splicing mechanisms

The doublesex/mab-3 related transcription factor (Dmrt) genes regulate sexual development in metazoans. Studies of the doublesex (dsx) gene in insects, in particular Drosophila melanogaster, reveal that alternative splicing of dsx generates sex-specific Dsx isoforms underlying sexual differentiation. Such a splicing-based mechanism underlying sex-specific Dmrt function is thought to be evolved from a transcription-based mechanism used in non-insect species, but how such transition occurs during evolution is not known. Here we identified a male-specific dsx transcript (dsx^M2) through intron retention (IR), in addition to previously identified dsx^M and dsx^F transcripts through alternative polyadenylation (APA) with mutually exclusive exons. We found that Dsx^M2 had similarly masculinizing function as Dsx^M. We also found that the IR-based mechanism generating sex-specific dsx transcripts was conserved from flies to cockroaches. Further analysis of these dsx transcripts suggested an evolutionary pathway from sexually monomorphic to sex-specific dsx via the sequential use of IR-based and APA-based alternative splicing.

An ancestral male-specific doublesex isoform, dsxM2, is identified via intron retention, with a masculinizing function weaker than the modern dsxM

The doublesex gene regulates dimorphic sexual and aggressive behaviors in Drosophila

Most animal species display dimorphic sexual behaviors and male-biased aggressiveness. Current models have focused on the male-specific product from the fruitless (fru^M) gene, which controls male courtship and male-specific aggression patterns in fruit flies, and describe a male-specific mechanism underlying sexually dimorphic behaviors. Here we show that the doublesex (dsx) gene, which expresses male-specific Dsx^M and female-specific Dsx^F transcription factors, functions in the nervous system to control both male and female sexual and aggressive behaviors. We find that Dsx is not only required in central brain neurons for male and female sexual behaviors, but also functions in approximately eight pairs of male-specific neurons to promote male aggressiveness and approximately two pairs of female-specific neurons to inhibit female aggressiveness. Dsx^F knockdown females fight more frequently, even with males. Our findings reveal crucial roles of dsx, which is broadly conserved from worms to humans, in a small number of neurons in both sexes to establish dimorphic sexual and aggressive behaviors.