OPPOSITE SEX DETERMINATION OF GONADS IN 2 PLEURODELES SPECIES MAY BE DUE TO A TEMPERATURE-DEPENDENT INACTIVATION OF SEX-CHROMOSOMES

In the urodele amphibians Pleurodeles waltl and Pleurodeles poireti, a rise from 20 degrees C to 30 degrees C-32 degrees C of rearing temper ature of larvae, when their gonads are still undifferentiated, leads t o sex reversal: the primordial gonads differentiate into testes in P. waltl ZW genotypic females and into ovaries in P. poireti ZZ genotypic males. in both cases, sex-reversed gonads produce fertile spermatozoa or oocytes. On the basis of results from intra- and interspecific cro sses, we conclude that sex reversal appears to segregate in the presen ce of peptidase-1 beta but not peptidase-1A. We propose that a heat-ac tivated sequence is localized in the vicinity of the peptidase-1 beta gene, which was demonstrated to be linked to W chromosome in P. waltl and to Z chromosome in P. poireti. This thermosensitive locus could ac t as a cis-inhibitor of sex determining genes during the heat treatmen t of larvae.