MURDOCK, C.A.; WIBBELS, T.; University of Alabama at Birmingham: Chronology of expression for potential sex-determining genes during temperature-dependent sex determination.

Temperature-dependent sex determination (TSD) has been observed in many species of reptiles. During TSD egg incubation temperatures influence the sex determination during a critical period of embryonic development (i.e., temperature-sensitive period or TSP), which coincides with the middle-third of incubation. A number of studies have shown that ovarian differentiation can occur in response to exogenous estrogen treatment during the TSP, even at male incubation temperatures. Such findings have lead to the hypothesis that estrogens may play an important role in TSD. Additionally, other potential sex-determining genes (first identified in mammalian systems) have also been identified in TSD reptiles. In order to address both the estrogen hypothesis and the potential roles of these putative sex-determining genes, quantitative competitive RT-PCR assays have been developed and used for determining the expression patterns for aromatase, Sf-1, and Dmrt1. Expression patterns were examined in adrenal-kidney-gonad complexes from embryonic stages 15, 17, 19, 21, 23, and 26 (hatch) for all of the aforementioned genes. Aromatase mRNA levels were not significantly different between males and females during the TSP. It was only after the TSP that aromatase expression was shown to be higher in females. A developmental surge in Sf-1 expression was observed during the TSP in both males and females, but no sex-specific difference was found during the TSP. However, for Dmrt1 a significant increase was observed during the TSP in males, while expression in females remained low. Thus, of the three genes examined, only Dmrt1 displayed a sexually dimorphic pattern of expression during the TSP, and therefore Dmrt1 could be involved in male sex-determination in reptiles with TSD.