New insights on the mechanism of testis differentiation from the morphogenesis of experimentally induced testes in genetically female chick embryos

Abstract

Embryonic testes grafted in the extraembryonic coelom of 3-day-old genetically female chick embryos may induce total and definitive reversal of gonadal sex differentiation. In this experimental condition, the left gonad becomes a testis instead of an ovary. This makes it possible to compare testicular and ovarian morphogenesis in animals having the same genetic sex and to discount what is due to differences in the genetic determination between male and female. The morphogenesis of such testes is marked by a disappearance of the cortical germinal epithelium. The medullary sex cords keep a narrow lumen instead of becoming large lacunae. The germ cells remain few in the sex cords and do not become meiotic. Furthermore, interstitial cell development is known to be very slow. As a consequence the gross size of the gonad is much smaller than that of an ovary. All these morphogenetic phenomena are unlike those observed during normal ovarian differentiation and evidence an inhibiting influence of the grafted testes. Since inhibition and masculinization are concomitant, inhibition appears to be the mechanism responsible for gonadal sex reversal. The extraembryonic situation of the grafted testes and their relation with the embryo only via the blood stream demonstrates the role of a secreted substance or substances still to be exactly identified. Previous data suggest that this could be the anti-Müllerian-hormone (AMH). Furthermore, previous and present results show that testis differentiation can be actively induced in a bird. This does not agree with the hypothesis that the gonads of the homogametic sex, i.e., the testes in birds, do not need any inducer in order to differentiate.(ABSTRACT TRUNCATED AT 250 WORDS)

Novel sex‐determining genes in fish and sex chromosome evolution

“…Similar expression patterns of the two genes were observed in the American alligator ( Alligator mississippiensis ) (Western et al, ). In addition, AMH is suspected to be a factor responsible for female‐to‐male sex reversal in the chicken, as determined by grafting undifferentiated testes into ZW female embryos (Maraud et al, ). The above‐mentioned findings in fish species corroborate this hypothesis.…”

The potential role of microRNAs in regulating gonadal sex differentiation in the chicken embryo

“…However, chicken AMH expression precedes that of SOX9 (Oreal et al 1998), at least at the mRNA level, suggesting that its activation is not dependent upon SOX9. Interestingly, male-to-female sex reversal, including Müllerian duct regression, can be induced by grafting a late stage embryonic testis to the vasculature of female chicken embryos prior to ovarian differentiation (Frankenhuis and Kappert 1980;Maraud et al 1990;Rashedi et al 1990). The likely factor inducing sex reversal in this instance is AMH, which may have a more central role in avian testis formation than it does in mammals.…”

Sex determination: insights from the chicken

“…(41) Female-to-male sex reversal in the chicken embryo can also be achieved by grafting embryonic testes onto ZW (genetic female) embryos prior to sexual differentiation. (42) In these cases, both gonads of ZW embryos can develop as testes. It is thought that the responsible factor secreted from the graft is Anti-Mü llerian Hormone (AMH).…”