Female-enriched expression of ERalpha during gonad differentiation of the urodele amphibian Pleurodeles waltl.

In the amphibian Pleurodeles waltl, estradiol treatment of genetically male larvae (ZZ) induces male-to-female sex reversal whereas heat treatment of genetically female larvae (ZW) inhibits estradiol synthesis and leads to female-to-male sex reversal. No data are available on estrogen receptors in this species. In the present study, we have isolated a unique full-length pwERalpha cDNA and its 5'-flanking region whose promoter activity was confirmed by transfection assays. RT-PCR studies performed in adult animals using ERalpha-specific primers, revealed that pwERalpha mRNA was present mainly in reproductive tissues: gonads, fat body and oviduct. PwERalpha transcript was also detected in liver, suggesting its implication in vitellogenesis control as in numerous oviparous species. The level of pwERalpha transcripts was also studied during gonad differentiation by quantitative real-time PCR. At stage 54(30d) pwERalpha expression in gonads of ZW larvae was significantly higher than in ZZ ones. This sex-specific discrimination was confirmed when gonad-mesonephros-interrenal complexes (GMI), taken at the same stage, were subjected to whole mount in situ hybridization. In comparison, the female-enriched expression of P450 aromatase, which was studied as a control of ovary differentiation, was observed earlier (stage 54). In ZW larvae reared at 32 degrees C, a condition leading to sex reversal, pwERalpha mRNA level at stage 54(30d) was lower than in control females. Taken together, these results showing a female-enriched and thermosensitive expression of pwERalpha suggest an important role for this receptor in gonad differentiation of the urodele amphibian Pleurodeles waltl.