Russell A J, Gilmore D P, Mackay S, Ullmann S L, Baker P J, Payne A P
Laboratory of Human Anatomy, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK.
Anat Embryol (Berl). 2003 Apr;206(5):381-9. doi: 10.1007/s00429-002-0300-7. Epub 2003 Feb 5.
In eutherian mammals, sex differentiation is initiated by expression of the testis-determining gene on the Y chromosome. Subsequent phenotypic development of the reproductive tract and genitalia depends on the production of hormones by the differentiated testis. In marsupials the mechanisms of phenotypic development may vary from this pattern, as differentiation of the scrotal primordia has been shown to occur before that of the gonad. Thus, the development of the scrotum in the marsupial has been regarded as an androgen-independent process. We have sought to clarify the ontogeny of scrotal development and the appearance of androgen receptor immunoreactivity by examining Monodelphis domesticaembryos/pups from 1 day prior to birth until 2 days after birth. We have also used immunocytochemistry to determine the expression of the key steroidogenic enzyme 3beta-hydroxysteroid dehydrogenase as an indicator of when the developing gonad may be capable of synthesizing androgens. Expression of this enzyme was first detected in the gonads and adrenals of both sexes 1 day prior to birth and before the appearance of scrotal bulges. Androgen receptor immunoreactivity was detected in the scrotal anlagen of male opossum pups as early as 1 day following birth. This finding is significantly earlier than previous reports and coincides with the appearance 1 day after birth of distinct scrotal bulges. Androgen receptor immunoreactivity was also observed in the genital tubercles of male pups, but not female pups, 2 days after birth. These results suggest that androgens may play an important role in the development of the male genitalia at a much earlier stage than that indicated by previously published work and that scrotal development in this species may not be androgen-independent.
在真兽亚纲哺乳动物中，性别分化由Y染色体上睾丸决定基因的表达启动。生殖道和生殖器随后的表型发育取决于分化后的睾丸产生的激素。在有袋类动物中，表型发育机制可能与这种模式不同，因为阴囊原基的分化已被证明发生在性腺分化之前。因此，有袋类动物阴囊的发育被认为是一个不依赖雄激素的过程。我们试图通过检查出生前1天到出生后2天的家短尾负鼠胚胎/幼崽，来阐明阴囊发育的个体发生以及雄激素受体免疫反应性的出现情况。我们还使用免疫细胞化学来确定关键类固醇生成酶3β - 羟基类固醇脱氢酶的表达，以此作为发育中的性腺何时能够合成雄激素的指标。该酶的表达在出生前1天、阴囊隆起出现之前，首先在两性的性腺和肾上腺中被检测到。雄性负鼠幼崽出生后1天，最早在阴囊原基中检测到雄激素受体免疫反应性。这一发现比之前的报道要早得多，并且与出生后1天明显的阴囊隆起的出现时间一致。出生后2天，在雄性幼崽的生殖结节中也观察到雄激素受体免疫反应性，但在雌性幼崽中未观察到。这些结果表明，雄激素可能在比先前发表的研究表明的更早阶段，就在雄性生殖器发育中发挥重要作用，并且该物种的阴囊发育可能并非不依赖雄激素。
