Expression of Sox9, Mis, and Dmrt1 in the gonad of a species with temperature‐dependent sex determination

Sex determination in vertebrates, the process of forming an ovary or testis from a bipotential gonad, can be initiated by genetic or environmental factors. Elements of the downstream molecular pathways underlying these different sex‐determining mechanisms have been evolutionarily conserved. We find the first evidence that Sox9 expression is preferentially organized in the testis early in the temperature‐sensitive period in a species with temperature‐dependent sex determination (Trachemys scripta). This pattern occurs before sexually dimorphic Mis expression and in a temporal hierarchy that is similar to mammals. Furthermore, we extend previous findings that Dmrt1 expression at early stages of sex determination has a dimorphic pattern consistent with a possible upstream role in determining the fate of the bipotential gonad. Developmental Dynamics 236:1055–1063, 2007. © 2007 Wiley‐Liss, Inc.