Action of estradiol and tamoxifen on the testis-inducing activity of the chick embryonic testis grafted to the female embryo.

The implantation of two testes from 13-day-old male chick donor embryos into the extra-embryonic celom of 3-day-old female embryos induces the masculinization of their ovaries up to a total and definitive inversion of their gonadal sex, i.e., the differentiation of testes in the female hosts. Pretreatment of the donors with estradiol (E2) between day 11 and 13 counteracts the testis-inducing activity of the implants, while co-treatment of donors with both tamoxifen (TAM) and E2 at the same stage restores the initially observed activity. The treatment of 3-day-old male donor embryos with E2 causes the differentiation of their left gonad into an ovotestis totally devoid of testis-inducing activity once grafted in the same conditions as above. An additional treatment with TAM of the grafted host embryos does not modify the results obtained when E2-treated male gonads are grafted to normal host embryos. This shows that the lack of testis-inducing activity exhibited by the E2-treated grafts can not be attributed to a protecting action of endogenous estrogens on the gonads of the host. On account of previous work showing the inhibition by E2 of the Müllero-regressive activity of the chick embryonic testis, our present results can be interpreted in terms of E2-down regulation of Anti-Müllerian Hormone (AMH or MIS), which appears to be a good candidate as testis-inducer. The relevance of our results to the phenomenon of gonad differentiation is discussed.