The multistage model of sex chromosome evolution. An endoplasmic reticulum protein, calreticulin, is transported into the acrosome of rat sperm. The next gene in the fly pathway, doublesex dsxis alternatively spliced to produce female-specific and male-specific isoforms of DSX proteins, which are master regulators of the female and male transcriptome, respectively [ Arbeitman et al.
Western et al. Figure 1. Although it is an XY system, the platypus' sex chromosomes share no homologues with eutherian sex chromosomes.
In contrast, the Y-chromosome ordinarily occurs only in one of the two sexes of a species, e. Most research on the molecular biology of sex determination in reptiles describes expression patterns for orthologs of mammalian sex-determining genes.
Alternative pre-mRNA splicing: the logic of combinatorial control. We understand GSD and TSD as two dichotomous sex-determining systems that do not differ in thermal dependency of sex ratios, but basically in the presence or absence of sex chromosomes.
In Pejerrey, a fish species with TSD, individuals treated with cortisol presented elevated levels of ketotestosterone KT and testosterone and typical molecular signatures of masculinization including up-regulation of amh expression and down-regulation of cyp19a1a expression [ ].
Because the amount of information on these novel pathways is quite limited, we focused our review on the cortisol-mediated pathway and the epigenetic regulatory pathway.
Based on these studies, it is tempting to speculate that methylation of the cyp19a promoter may participate in the mechanism that links environmental temperature and sex ratios in vertebrate species with TSD but future research is necessary to support this hypothesis.
Thus, ESR females i. Expression differences are taken as evidence that the gene of interest is involved in TSD. Pieau Biology. The genetic risk associated with stock enhancement of fish with TSD, for example in the Japanese flounder, [ ], or the consequences of ESR induced by climate changes temperature variation on populations [ ], have been theoretically evaluated.
Evolution of sex determining mechanisms. Trends Endocrinol Metab.
Cytogenetics : chromosomes. In reptiles, the gene is not differentially expressed in response to temperature variation during the TSP, therefore, its role in reptile sex determination is unclear. We have used differential display PCR to identify genes that are differentially expressed in gonads early in the temperature-sensitive period in the common snapping turtle.