Mechanism for Developmental Regulation by Genomic Imprinting in the Female Germ Line.

在哺乳动物中，配子发生过程中基因组的表观遗传修饰导致亲本等位基因和发育所必需的印记基因的表达不对等。为了更深入地了解基因组印记，我们做了几条线的实验。首先，为了准确地研究母体初级印记建立的时间和方式，我们从1到20天的小鼠的非生长期或生长期的卵母细胞中获得了包含一个基因组的孤雌胚胎，并从成年小鼠的完全发育的卵母细胞中获得了一个基因组。利用这些胚胎对8个印记基因：Snrpn、Znfl27、NDN、Peg3、Igf2r、p57^&lt；Kip2&gt；、Peg1和Impact进行了表达分析。结果表明，每个印记基因的表观遗传标记并不是在卵母细胞生长过程中的某一特定时刻一起施加的，而是在初级卵泡期到有腔卵泡期的大范围内出现的。构建的孤雌生殖…的发育能力随着核供体卵母细胞的生长，更多的ic胚胎逐渐减少。因此，本研究清楚地表明，在卵母细胞的生长阶段，母体的初级印记是以一种循序渐进的方式发生的。其次，我们研究了H19单等位基因表达的调节是否提高了孤雌胚胎的存活率。结果表明，携带H19转录单位缺失的ng-卵母细胞基因组的ng/FG孤雌胚胎在17.5天内成功发育为活胎。对照实验表明，这一独特现象的发生与遗传背景效应无关。组织学分析表明，单性生殖胎盘出现萎缩，并伴有严重的中性粒细胞增多等异常。本研究结果提示，H19基因在ng等位基因表达的停止导致了胚胎发育的延长，胎盘功能缺陷对个体发育可能是致命的。较少

In mammals, epigenetic modification of genomes during gametogenesis leads to an unequivalent expression of imprinted genes between parental alleles and necessary for term development. To understand the further insight into genomic imprinting we have done several lines of experiment. Firstly, to investigate when and how, precisely, maternal primary imprinting is established, we produced parthenogenetic embryos containing one genome from a non-growing or growth stage oocyte from 1- to 20-day old mice, and one from a fully-grown oocyte from adult mice. Using these embryos, expression analysis of eight imprinted genes, Snrpn, Znfl27, Ndn, Peg3, Igf2r, p57^<KIP2>, Peg1 and Impact, was conducted. The results show that the epigenetic markers for each imprinted gene are not imposed all together at a specific time during oocyte growth, but rather occurs within a wide range during the period from primary to antral follicle stage oocytes. The developmental ability of the constructed parthenogenet … More ic embryos is gradually reduced with the growth of nuclear donor oocytes. Thus, the present study clearly demonstrate that maternal primary imprinting occurs in a stepwise fashion for groups of imprinted genes during the oocyte growth stages. Secondly, we examined whether the regulation of H19 monoallelic expression enhances the survival of parthenogenetic embryos. The results clearly show that the ng/fg parthenogenetic embryos carrying the ng-oocyte genome that had been deleted by the H19 transcription unit successfully developed as live fetuses for 17.5 gestation days. Control experiments revealed that this unique phenomenon occurs irrespective of the genetic background effect. Histological analysis showed that the placenta of ng^<H19-KO>/fg^<WT> parthenotes was resulted in atrophia with sever negro-cytosis and other anomalies. The present results suggest that the cessation of H19 gene expression from the ng-allele causes the extended development and that functional defection of the placenta could be fatal for the ontogeny. Less