Baker P J, Moore H D, Burgess A M, Mittwoch U
Department of Anatomy, Queen Mary and Westfield College, London, UK.
J Anat. 1993 Apr;182 ( Pt 2)(Pt 2):267-73.
Growth and histological differentiation were studied in 8 litters of embryos and 4 litters of neonate grey short-tailed opossums, Monodelphis domestica. The embryonic litters included 2 that had passed their expected birth date, and whose weights exceeded the usual birthweights; we refer to these litters as 'postmature'. There was an abrupt increase in the growth rate of XY gonads after birth, but this was not seen in XX gonads. Although there was evidence of testicular differentiation in XY gonads on the day before the expected birth, testicular differentiation was found to be blocked in postmature litters. The growth of XX gonads in postmature embryos was not affected. In view of evidence that exogenous oestrogens feminise the gonads of genetic males in some species of marsupials including Monodelphis domestica, the question arises whether oestrogen is responsible for the failure of testes to continue their development in utero. We suggest that the ability of functional testes to develop in the presence of oestrogen may be a fundamental requirement distinguishing eutherian mammals from other vertebrates, including marsupials.
对8窝胚胎和4窝新生灰短尾负鼠（Monodelphis domestica）的生长和组织学分化进行了研究。胚胎窝中有2窝超过了预期出生日期，其体重超过了正常出生体重；我们将这些窝称为“过熟”。出生后XY性腺的生长速率突然增加，但XX性腺未出现这种情况。尽管在预期出生前一天XY性腺有睾丸分化的证据，但发现在过熟窝中睾丸分化受阻。过熟胚胎中XX性腺的生长未受影响。鉴于有证据表明外源性雌激素会使包括Monodelphis domestica在内的一些有袋类物种的遗传雄性性腺雌性化，问题就出现了，即雌激素是否是睾丸在子宫内无法继续发育的原因。我们认为，功能性睾丸在雌激素存在下发育的能力可能是区分真兽类哺乳动物与包括有袋类在内的其他脊椎动物的一个基本要求。
