Feil R, Khosla S, Cappai P, Loi P
Programme in Developmental Genetics, The Babraham Institute, Cambridge CB2 4AT, United Kingdom.
Mamm Genome. 1998 Oct;9(10):831-4. doi: 10.1007/s003359900876.
Studies in the mouse have established that both parental genomes are essential for normal embryonic development. Parthenogenetic mouse embryos (which have two maternal genomes and no paternal genome), for example, are growth-retarded and die at early postimplantation stages. The distinct maternal and paternal contributions are mediated by genomic imprinting, an epigenetic mechanism by which the expression of certain genes is dependent on whether they are inherited from mother or father. Although comparative studies have established that many imprinted mouse (and rat) genes are allele-specifically expressed in humans as well (and vice versa), so far imprinting studies have not been performed in other mammalian species. When considering evolutionary theories of genomic imprinting, it would be important to know how widely it is conserved among placental mammals. We have investigated its conservation in a bovid ruminant, the domestic sheep, by comparing parthenogenetic and normal control embryos. Our study establishes that, like in the mouse, parthenogenetic development in sheep is associated with growth-retardation and does not proceed beyond early fetal stages. These developmental abnormalities are most likely caused by imprinted genes. We demonstrate that, indeed, like in mice and humans, the growth-related PEG1/MEST and Insulin-like Growth Factor 2 (IGF2) genes are expressed from the paternal chromosome in sheep. These observations suggest that genomic imprinting is conserved in a third, evolutionarily rather diverged group of placental mammals, the ruminants.
对小鼠的研究已证实，双亲基因组对正常胚胎发育至关重要。例如，孤雌生殖的小鼠胚胎（有两个母本基因组且无父本基因组）生长迟缓，在植入后早期阶段死亡。母本和父本的不同贡献是由基因组印记介导的，这是一种表观遗传机制，某些基因的表达取决于它们是从母亲还是父亲遗传而来。尽管比较研究已证实，许多印记小鼠（和大鼠）基因在人类中也呈等位基因特异性表达（反之亦然），但到目前为止，尚未在其他哺乳动物物种中进行印记研究。在考虑基因组印记的进化理论时，了解其在胎盘哺乳动物中的保守程度有多广泛将很重要。我们通过比较孤雌生殖胚胎和正常对照胚胎，研究了其在一种牛科反刍动物——家养绵羊中的保守情况。我们的研究证实，与小鼠一样，绵羊的孤雌生殖发育与生长迟缓相关，且不会超过胎儿早期阶段。这些发育异常很可能是由印记基因引起的。我们证明，实际上，与小鼠和人类一样，与生长相关的PEG1/MEST和胰岛素样生长因子2（IGF2）基因在绵羊中从父本染色体表达。这些观察结果表明，基因组印记在胎盘哺乳动物的第三个进化上相当不同的群体——反刍动物中是保守的。
