Temperature induced-masculinisation in the Nile tilapia causes rapid up-regulation of both dmrt1 and amh expressions.

Nile tilapia has primarily a XX/XY sex determining system but minor genetic factors as well as temperature can override the major factors. Female XX progenies can be sex-reversed into functional males by rearing at high temperatures (>34°C) from 10dpf onwards. Temperature effects on the molecular pathways during sex differentiation in teleosts need to be deciphered. The temporal expression profiles of cyp19a1a and foxl2, two ovarian-developmental genes and dmrt1 and amh, two testes-developmental genes were analysed during key stages of the sex differentiation of genetic all-females, all-males and temperature-masculinised XX females (TM) tilapia. Overall QPCR analysis was similar between gonads and trunks. Both amh and dmrt1 expressions were up-regulated simultaneously in TM already at 13-15dpf. Dmrt1 expression became markedly elevated ∼3-fold higher than XY male levels at 20-26dpf whereas amh had similar levels to XY males. Foxl2 and cyp19a1a expression profiles were similar. Both were up-regulated at early stages in TM but repressed after 17-19dpf, whilest levels continued to increase in XX-females. Our results show that temperature action on tilapia testis development induces the rapid increase of both dmrt1 and amh expressions followed by the down-regulation of foxl2 and cyp19a1a. This suggests that dmrt1 and/or amh may be the modulator(s) of the down-regulation of foxl2 and/or cyp19a1a.