Evolution of sex-specific traits through changes in HOX-dependent doublesex expression.

Almost every animal lineage is characterized by unique sex-specific traits, implying that such traits are gained and lost frequently in evolution. However, the genetic mechanisms responsible for these changes are not understood. In Drosophila, the activity of the sex determination pathway is restricted to sexually dimorphic tissues, suggesting that spatial regulation of this pathway may contribute to the evolution of sex-specific traits. We examine the regulation and function of doublesex (dsx), the main transcriptional effector of the sex determination pathway, in the development and evolution of Drosophila sex combs. Sex combs are a recent evolutionary innovation and show dramatic diversity in the relatively few Drosophila species that have them. We show that dsx expression in the presumptive sex comb region is activated by the HOX gene Sex combs reduced (Scr), and that the male isoform of dsx up-regulates Scr so that both genes become expressed at high levels in this region in males but not in females. Precise spatial regulation of dsx is essential for defining sex comb position and morphology. Comparative analysis of Scr and dsx expression reveals a tight correlation between sex comb morphology and the expression patterns of both genes. In species that primitively lack sex combs, no dsx expression is observed in the homologous region, suggesting that the origin and diversification of this structure were linked to the gain of a new dsx expression domain. Two other, distantly related fly lineages that independently evolved novel male-specific structures show evolutionary gains of dsx expression in the corresponding tissues, where dsx may also be controlled by Scr. These findings suggest that changes in the spatial regulation of sex-determining genes are a key mechanism that enables the evolution of new sex-specific traits, contributing to some of the most dramatic examples of phenotypic diversification in nature.

Dynamic, mating-induced gene expression changes in female head and brain tissues of Drosophila melanogaster.

BACKGROUND: Drosophila melanogaster females show changes in behavior and physiology after mating that are thought to maximize the number of progeny resulting from the most recent copulation. Sperm and seminal fluid proteins induce post-mating changes in females, however, very little is known about the resulting gene expression changes in female head and central nervous system tissues that contribute to the post-mating response. RESULTS: We determined the temporal gene expression changes in female head tissues 0-2, 24, 48 and 72 hours after mating. Females from each time point had a unique post-mating gene expression response, with 72 hours post-mating having the largest number of genes with significant changes in expression. At most time points, genes expressed in the head fat body that encode products involved in metabolism showed a marked change in expression. Additional analysis of gene expression changes in dissected brain tissues 24 hours post-mating revealed changes in transcript abundance of many genes, notably, the reduced transcript abundance of genes that encode ion channels. CONCLUSIONS: Substantial changes occur in the regulation of many genes in female head tissues after mating, which might underlie aspects of the female post-mating response. These results provide new insights into the physiological and metabolic changes that accompany changes in female behaviors.

Doublesex establishes sexual dimorphism in the Drosophila central nervous system in an isoform-dependent manner by directing cell number.

doublesex (dsx) encodes sex-specific transcription factors (DSX(F) in females and DSX(M) in males) that act at the bottom of the Drosophila somatic sex determination hierarchy. dsx, which is conserved among diverse taxa, is responsible for directing all aspects of Drosophila somatic sexual differentiation outside the nervous system. The role of dsx in the nervous system remainsminimally understood. Here, the mechanisms by which DSX acts to establish dimorphism in the central nervous system were examined. This study shows that the number of DSX-expressing cells in the central nervous system is sexually dimorphic during both pupal and adult stages. Additionally, the number of DSX-expressing cells depends on both the amount of DSX and the isoform present. One cluster of DSX-expressing neurons in the ventral nerve cord undergoes female-specific cell death that is DSX(F)-dependent. Another DSX-expressing cluster in the posterior brain undergoes more cell divisions in males than in females. Additionally, early in development, DSX(M) is present in a portion of the neural circuitry in which the male-specific product of fruitless (fru) is produced, in a region that has been shown to be critical for sex-specific behaviors. This study demonstrates that DSX(M) and FRU(M) expression patterns are established independent of each other in the regions of the central nervous system examined. In addition to the known role of dsx in establishing sexual dimorphism outside the central nervous system, the results demonstrate that DSX establishes sex-specific differences in neural circuitry by regulating the number of neurons using distinct mechanisms.

Somatic, germline and sex hierarchy regulated gene expression during Drosophila metamorphosis.

BACKGROUND: Drosophila melanogaster undergoes a complete metamorphosis, during which time the larval male and female forms transition into sexually dimorphic, reproductive adult forms. To understand this complex morphogenetic process at a molecular-genetic level, whole genome microarray analyses were performed. RESULTS: The temporal gene expression patterns during metamorphosis were determined for all predicted genes, in both somatic and germline tissues of males and females separately. Temporal changes in transcript abundance for genes of known functions were found to correlate with known developmental processes that occur during metamorphosis. We find that large numbers of genes are sex-differentially expressed in both male and female germline tissues, and relatively few are sex-differentially expressed in somatic tissues. The majority of genes with somatic, sex-differential expression were found to be expressed in a stage-specific manner, suggesting that they mediate discrete developmental events. The Sex-lethal paralog, CG3056, displays somatic, male-biased expression at several time points in metamorphosis. Gene expression downstream of the somatic, sex determination genes transformer and doublesex (dsx) was examined in two-day old pupae, which allowed for the identification of genes regulated as a consequence of the sex determination hierarchy. These include the homeotic gene abdominal A, which is more highly expressed in females as compared to males, as a consequence of dsx. For most genes regulated downstream of dsx during pupal development, the mode of regulation is distinct from that observed for the well-studied direct targets of DSX, Yolk protein 1 and 2. CONCLUSION: The data and analyses presented here provide a comprehensive assessment of gene expression during metamorphosis in each sex, in both somatic and germline tissues. Many of the genes that underlie critical developmental processes during metamorphosis, including sex-specific processes, have been identified. These results provide a framework for further functional studies on the regulation of sex-specific development.

Ecdysone receptor acts in fruitless- expressing neurons to mediate drosophila courtship behaviors.

In Drosophila melanogaster, fruitless (fru) encodes male-specific transcription factors (FRU(M); encoded by fru P1) required for courtship behaviors (reviewed in). However, downstream effectors of FRU(M) throughout development are largely unknown. During metamorphosis the nervous system is remodeled for adult function, the timing of which is coordinated by the steroid hormone 20-hydroxyecdysone (ecdysone) through the ecdysone receptor, a heterodimer of the nuclear receptors EcR (isoforms are EcR-A, EcR-B1, or EcR-B2) and Ultraspiracle (USP) (reviewed in). Here, we show that genes identified as regulated downstream of FRU(M) during metamorphosis are significantly overrepresented with genes known to be regulated in response to ecdysone or EcR. FRU(M) and EcR isoforms are coexpressed in neurons in the CNS during metamorphosis in an isoform-specific manner. Reduction of EcR-A levels in fru P1-expressing neurons of males caused a significant increase in male-male courtship activity and significant reduction in size of two antennal lobe glomeruli. Additional genes were identified that are regulated downstream of EcR-A in fru P1-expressing neurons. Thus, EcR-A is required in fru P1-expressing neurons for wild-type male courtship behaviors and the establishment of male-specific neuronal architecture.

Positive regulation of IkappaB kinase signaling by protein serine/threonine phosphatase 2A.

Transcription factor NF-kappaB plays a key regulatory role in the cellular response to pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF). In the absence of TNF, NF-kappaB is sequestered in the cytoplasm by inhibitory IkappaB proteins. Phosphorylation of IkappaBby the beta-catalytic subunit of IKK, a multicomponent IkappaB kinase, targets the inhibitor for proteolytic destruction and facilitates nuclear translocation of NF-kappaB. This pathway is initiated by TNF-dependent phosphorylation of T loop serines in IKKbeta, which greatly stimulates IkappaB kinase activity. Prior in vitro mixing experiments indicate that protein serine/threonine phosphatase 2A (PP2A) can dephosphorylate these T loop serines and inactivate IKK, suggesting a negative regulatory role for PP2A in IKK signaling. Here we provided several in vivo lines of evidence indicating that PP2A plays a positive rather than a negative role in the regulation of IKK. First, TNF-induced degradation of IkappaB is attenuated in cells treated with okadaic acid or fostriecin, two potent inhibitors of PP2A. Second, PP2A forms stable complexes with IKK in untransfected mammalian cells. This interaction is critically dependent on amino acid residues 121-179 of the IKKgamma regulatory subunit. Third, deletion of the PP2A-binding site in IKKgamma attenuates T loop phosphorylation and catalytic activation of IKKbeta in cells treated with TNF. Taken together, these data provide strong evidence that the formation of IKK.PP2A complexes is required for the proper induction of IkappaB kinase activity in vivo.