Renfree M B, Shaw G
Department of Zoology, The University of Melbourne, Victoria, Australia.
Int J Dev Biol. 2001;45(3):557-67.
The formation of the testis or ovary is a critical step in development. Alterations in gonadal development during fetal or postnatal life can lead to intersexuality or infertility. Several model systems have been particularly useful in studying gonadal differentiation, the eutherian mammal and amphibia, fish, and birds. However, marsupials provide a unique opportunity to investigate gonadal development and the interactions of genes and hormones in gonadal differentiation and germ cell development in all mammals. On the one hand the genetic mechanisms appear to be identical to those in eutherian mammals, including the testis-determining SRY gene. On the other hand, marsupials retain in part the plasticity of the amphibian gonad to hormonal manipulation. It is possible to induce female to male and also male to female gonadal sex reversal in marsupials by hormonal manipulation, and oestradiol can induce male germ cells to enter meiosis at the time the oogonia do. In addition, in marsupials the development of the scrotum and mammary glands are independent of testicular androgens and instead are controlled by a gene or genes on the X-chromosome. Thus marsupials provide a number of opportunities for manipulating the sexual differentiation of the gonads that are not possible in eutherian mammals and so provide a unique perspective for understanding the common mechanisms controlling sexual development.
睾丸或卵巢的形成是发育过程中的关键步骤。胎儿期或出生后性腺发育的改变可导致雌雄间性或不育。在研究性腺分化方面，有几种模式系统特别有用，包括真兽亚纲哺乳动物、两栖动物、鱼类和鸟类。然而，有袋类动物为研究所有哺乳动物的性腺发育以及性腺分化和生殖细胞发育过程中基因与激素的相互作用提供了独特的机会。一方面，其遗传机制似乎与真兽亚纲哺乳动物相同，包括决定睾丸的SRY基因。另一方面，有袋类动物部分保留了两栖动物性腺对激素调控的可塑性。通过激素调控，有可能在有袋类动物中诱导雌性向雄性以及雄性向雌性的性腺性反转，并且雌二醇能在卵原细胞进入减数分裂时诱导雄性生殖细胞进入减数分裂。此外，在有袋类动物中，阴囊和乳腺的发育独立于睾丸雄激素，而是由X染色体上的一个或多个基因控制。因此，有袋类动物为操纵性腺的性别分化提供了许多在真兽亚纲哺乳动物中无法实现的机会，从而为理解控制性发育的共同机制提供了独特的视角。
