Aromatase activity in larval gonads of Pleurodeles waltl (Urodele Amphibia) during normal sex differentiation and during sex reversal by thermal treatment effect.

Estrogens are involved in gonadal differentiation in birds and in reptiles with temperature-dependent sex determination, suggesting a key role for aromatase, the enzyme complex converting androgens to estrogens. Pleurodeles waltl is an amphibian with ZZ/ZW genotypic sex determination but gonadal differentiation is thermosensitive. The sexual phenotype is in conformity with the sexual genotype at ambient temperature (20 +/- 2 degrees), but ZW animals are sex-reversed in functional males when larvae are reared at 32 degrees from stage 42 to stage 54 (thermosensitive period). Histological sexual differentiation of gonads begins at stage 53. Aromatase activity was measured either in the gonadmesonephric complexes (stages 47 to 52) or in the gonads (stages 53 to 56) of ZZ and ZW larvae reared at ambient temperature or at 32 degrees and of ZW larvae shifted at stages 53, 55, or 56 from ambient temperature to 32 degrees for 48 hr. At ambient temperature, aromatase activity was detected, at low levels, in gonad-mesonephric complexes of both ZZ and ZW larvae at stages 47 and 50. At stage 52, it was significantly higher in ZW individuals than in ZZ ones. Then it remained low in gonads of ZZ males, whereas it markedly increased in gonads of ZW females. At 32 degrees, the gonad-mesonephric complexes (stage 52) and the gonads (stages 53 to 56) of ZW larvae had low aromatase activity similar to that in ZZ individuals. The exposure to 32 degrees for 48 hr of ZW individuals significantly decreased gonadal aromatase activity during the thermosensitive period (shift at stage 53) but not after the thermosensitive period (shifts at stages 55 and 56).(ABSTRACT TRUNCATED AT 250 WORDS)