Important differences are detected in the gene expression profiles of bipotential gonads that either develop into ovaries under the effect of female-promoting temperature (FPT), or form ovaries when induced with exogenous E2 at the male promoting temperature (MPT) (Matsumoto et al., 2013; Ramsey and Crews, 2009; Valenzuela et al., 2013). For example, steroid hormone re- ceptors (ER alpha, ER beta and androgen receptor) show different expression patterns in Chelydra serpentina and Trachemys scripta (Ramsey and Crews, 2007). However, since the MPT and FPT induce dimorphic expression of aromatase at the end of the temperature-sensitive period
) thresholds of en- dogenous E2 levels involved in gonadal differentiation may be tightly regulated by temperature prior to the stabilization of transcriptional networks. Steroid hormone and metabolite levels in developing gonads depend on regulatory gene networks. These mainly involve autonomous cell transcription, cell-cell signaling and transducing factors. In mammals and birds, FoxL2 regulates aromatase expression . Similar regulation is inferred in reptiles with TSD; however, direct evidence is not yet available. In the slider turtle, higher FoxL2 and aromatase levels are expressed in gonads from embryos at FPT than at MPT ). Furthermore, gonads of the snapping turtle Chelydra serpentina shifted from MPT to FPT show up-reg- ulation of FoxL2 and aromatase