Old experiments and new trends in avian sex differentiation |
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Authors: | Etienne Wolff |
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Institution: | (1) Collège de France, II, Place Marcelin Berthelot, 75005 Paris, France |
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Abstract: | Summary The influence of steroid hormones on sex differentiation was first demonstrated in birds in 1935. Steroid female hormones
injected in vivo into male embryos determined a partial or total feminization of gonads and genital ducts. Male hormones determined
only the sex reversal of the ducts. Some substances of the group of androgens, such as dehydroandrosterone, had a paradoxical
effect; they feminized males and masculinized females. Similar effects were observed later by several authors in all groups
of vertebrates. In placentary mammals, only genital ducts were transformed. Castration of avian embryos also demonstrated
the role of embryonic sexual hormones on genital ducts. These results, first obtained in vivo, were confirmed by experiments
in vitro. Since then numerous studies have been undertaken on the nature of the hormone responsible for the regression of
müllerian ducts in embryos of birds and other groups of vertebrates. Some authors assumed that these substances are proteins;
many offered new evidence for the role of steroid sexual hormones during sex differentiation. Thus the problem appeared more
complicated than it was thought at first. In recent years, synthesis of steroid sexual hormones have been demonstrated in
young embryos during or even before sex differentiation; and enzymes that catalyze the synthesis of these hormones, such as
hydroxysteroiddehydrogenase, also have been discovered. Further research has been oriented toward the characterization of
steroid hormones by techniques of immunochemistry and labeled isotopes confirming the results obtained by other techniques.
Specific proteins are being isolated in the effectors; they work as receptors of steroid hormones. Nuclear receptors of estradiol
have been discovered in the embryonic gonads and in the cloacal wall at the time of sexual differentiation. Thus a mechanism
can be conceived in which proteins and steroid hormones play mutual roles in the process of sex differentiation.
Presented in the formal symposium on Sexual Differentiation in Vitro and in Vivo at the 29th Annual Meeting of the Tissue
Culture Association, Denver, Colorado, June 4–8, 1978. |
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Keywords: | embryo gonads differentiation androgens estrogens |
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