Opposite Sex Determination of Gonads in Two Pleurodeles Species May Be Due to a Temperature-Dependent Inactivation of Sex Chromosomes

In the urodele amphibians Pleurodeles waltl and Pleurodeles polretl, a rise from 20°C to 30°C-32°C of rearing temperature of larvae, when their gonads are still undlfferentiated, leads to sex reversal: the primordial gonads differentiate Into testes in P. waltl ZW genotypic females and Into ovaries In P. polreti ZZ genotyplc males. In both cases, sex-reversed gonads produce fertile spermatozoa or oocytes. On the basis of results from Intraand interspecific crosses, we conclude that sex reversal appears to segregate In the presence of peptidase-1 p but not peptidase1A. We propose that a heat-activated sequence is localized in the vicinity of the peptidase-1 p gene, which was demonstrated to be linked to W chromosome in P. waltl and to Z chromosome In P. polretl. This thermosensltlve locus could act as a cis-lnhibitor of sex determining genes during the heat treatment of larvae.