An avian sexual revolution

Identification of genes related to sexual differentiation and sterility in embryonic gonads of Mule ducks by transcriptome analysis

The key genes of avian gonadal development are of great significance for sex determination. Transcriptome sequencing analysis of Mule duck gonad as potential sterile model is expected to screen candidate genes related to avian gonad development. In this study, the embryonic gonadal tissues of Mule ducks, Jinding ducks, and Muscovy ducks were collected and identified. Six sample groups including female Mule duck (A), male Mule duck (B), female Jinding duck (C), male Jinding duck (D), female Muscovy duck (E), and male Muscovy duck (F) were subjected to RNA sequencing analysis. A total of 9,471 differential genes (DEGs) and 691 protein-protein interaction pairs were obtained. Totally, 12 genes (Dmrt1, Amh, Sox9, Tex14, Trim71, Slc26a8, Spam1, Tdrp, Tsga10, Boc, Cxcl14, and Hsd17b3) were identified to be specifically related to duck testicular development, and 11 genes (Hsd17b1, Cyp19a1, Cyp17a1, Hhipl2, Tdrp, Uts2r, Cdon, Axin2, Nxph1, Brinp2, and Brinp3) were specifically related to duck ovarian development. Seven genes (Stra8, Dmc1, Terb1, Tex14, Tsga10, Spam1, and Plcd4) were screened to be specifically involved in the female sterility of Mule ducks; eight genes (Gtsf1, Nalcn, Tat, Slc26a8, Kmo, Plcd4, Aldh4a1, and Hgd) were specifically involved in male sterility; and five genes (Terb1, Stra8, Tex14 Tsga10 and Spam1) were involved in both female and male sterility. This study provides an insight into the differential development between male and female gonads of ducks and the sterility mechanism of Mule ducks through function, pathway, and protein interaction analyses. Our findings provide theoretical basis for the further research on sex determination and differentiation of birds and the sterility of Mule ducks.

Changes in gonadal gene network by exogenous ligands in temperature-dependent sex determination

We examined the expression of candidate sex-determining genes in the red-eared slider turtle (Trachemys scripta) during the temperature-sensitive period (TSP). Aromatase and Rspo1 were used as markers of ovarian differentiation and Sox9 was used as a marker of testicular differentiation. Eggs were incubated at a male-producing temperature (26 °C or MPT) and a female-producing temperature (31 °C or FPT). First, eggs at the beginning of the TSP (stage 16) were topically treated with the steroid hormones 17β-estradiol (E2), testosterone in combination with aromatase inhibitor (AI+T), the E2 antagonist (ICI 182 780), and the androgen antagonist (flutamide). Secondly, gonads were removed at stage 16 and treated in vitro with E2, AI+T, or hormone antagonists. At the FPT, AI+T in ovo suppressed aromatase and Rspo1, while activating Sox9. At the MPT, E2 treatment rapidly increased aromatase and Rspo1, while suppressing Sox9. Treatment with the E2 antagonist in ovo decreased aromatase at the FPT. Treatment with the androgen antagonist in ovo increased aromatase and Rspo1 at early time points at MPT and decreased Sox9 at MPT at later developmental stages. Treatment of isolated gonads cultured in vitro with AI+T at FPT decreased aromatase and Rspo1 and E2 increased the expression of these genes at MPT. In vitro treatment with E2 antagonist suppressed aromatase and Rspo1 expression at FPT. Overall, our results suggest that exogenous ligands dictate gonadal development by redirecting the expression of candidate sex-determining genes within the genetic cascades induced by temperature.

Sex determination strategies in 2012: towards a common regulatory model?

Sex determination is a complicated process involving large-scale modifications in gene expression affecting virtually every tissue in the body. Although the evolutionary origin of sex remains controversial, there is little doubt that it has developed as a process of optimizing metabolic control, as well as developmental and reproductive functions within a given setting of limited resources and environmental pressure. Evidence from various model organisms supports the view that sex determination may occur as a result of direct environmental induction or genetic regulation. The first process has been well documented in reptiles and fish, while the second is the classic case for avian species and mammals. Both of the latter have developed a variety of sex-specific/sex-related genes, which ultimately form a complete chromosome pair (sex chromosomes/gonosomes). Interestingly, combinations of environmental and genetic mechanisms have been described among different classes of animals, thus rendering the possibility of a unidirectional continuous evolutionary process from the one type of mechanism to the other unlikely. On the other hand, common elements appear throughout the animal kingdom, with regard to a) conserved key genes and b) a central role of sex steroid control as a prerequisite for ultimately normal sex differentiation. Studies in invertebrates also indicate a role of epigenetic chromatin modification, particularly with regard to alternative splicing options. This review summarizes current evidence from research in this hot field and signifies the need for further study of both normal hormonal regulators of sexual phenotype and patterns of environmental disruption.