McKay L M, Wrigley J M, Graves J A
Department of Genetics and Human Variation, La Trobe University, Bundoora, Vic.
Aust J Biol Sci. 1987;40(4):397-404. doi: 10.1071/bi9870397.
The inactive mammalian X-chromosome is always late-replicating, and in eutherian mammals it is heterochromatic and hypermethylated. We propose that this multistep system has evolved from a more primitive system, remnants of which may be found in marsupials and monotremes. The heterochromatic X (sex-chromatin body) is a distinctive feature of interphase cells of certain tissues in eutherian females but not males. Thus we have searched for a sex-specific chromatin body in these same tissues in marsupials (brush-tail possum, Trichosurus vulpecula) and monotremes (platypus, Ornithorynchus anatinus), using classical histological techniques. A female-specific chromatin body was observed at low frequency in nuclei of possum corneal epithelium, but not in any other tissues. No sex difference was observed in any monotreme tissue. These data suggest that stabilization of X-chromosome inactivation by heterochromatinization is tissue-specific in marsupials and absent in monotremes.
无活性的哺乳动物X染色体总是进行晚复制，在真兽亚纲哺乳动物中，它是异染色质且高度甲基化的。我们提出，这个多步骤系统是从一个更原始的系统进化而来的，在有袋类动物和单孔目动物中可能会发现其残余部分。异染色质X（性染色质体）是真兽亚纲雌性而非雄性某些组织间期细胞的一个显著特征。因此，我们使用经典组织学技术，在有袋类动物（帚尾袋貂，Trichosurus vulpecula）和单孔目动物（鸭嘴兽，Ornithorynchus anatinus）的相同组织中寻找性别特异性染色质体。在袋貂角膜上皮细胞核中低频观察到雌性特异性染色质体，但在其他任何组织中均未观察到。在任何单孔目动物组织中均未观察到性别差异。这些数据表明，在有袋类动物中，通过异染色质化使X染色体失活的稳定作用具有组织特异性，而在单孔目动物中则不存在。
