Faculty of Life and Environmental Sciences, Life Science Center for Survival Dynamics, Tsukuba Advanced Research Alliance (TARA), University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Ibaraki, 305-8577, Japan.
Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8577, Japan.
Epigenetics Chromatin. 2023 Feb 17;16(1):7. doi: 10.1186/s13072-023-00482-x.
Allele-specific methylation of the imprinting control region (ICR) is the molecular basis for the genomic imprinting phenomenon that is unique to placental mammals. We previously showed that the ICR at the mouse H19 gene locus (H19 ICR) was unexpectedly established after fertilization and not during spermatogenesis in transgenic mice (TgM), and that the same activity was essential for the maintenance of paternal methylation of the H19 ICR at the endogenous locus in pre-implantation embryos. To examine the universality of post-fertilization imprinted methylation across animal species or imprinted loci, we generated TgM with two additional sequences.
The rat H19 ICR, which is very similar in structure to the mouse H19 ICR, unexpectedly did not acquire imprinted methylation even after fertilization, suggesting a lack of essential sequences in the transgene fragment. In contrast, the mouse IG-DMR, the methylation of which is acquired during spermatogenesis at the endogenous locus, did not acquire methylation in the sperm of TgM, yet became highly methylated in blastocysts after fertilization, but only when the transgene was paternally inherited. Since these two sequences were evaluated at the same genomic site by employing the transgene co-placement strategy, it is likely that the phenotype reflects the intrinsic activity of these fragments rather than position-effect variegation.
Our results suggested that post-fertilization imprinted methylation is a versatile mechanism for protecting paternal imprinted methylation from reprogramming during the pre-implantation period.
印迹控制区（ICR）的等位基因特异性甲基化是胎盘哺乳动物所特有的基因组印迹现象的分子基础。我们之前曾表明，在转基因小鼠（TgM）中，H19 基因座的 ICR（H19 ICR）是在受精后而不是在精子发生过程中建立的，并且相同的活性对于维持前植入胚胎中内源 H19 ICR 的父系甲基化是必需的。为了检查受精后印迹性甲基化在动物物种或印迹基因座中的普遍性，我们用两个额外的序列生成了 TgM。
大鼠 H19 ICR 与小鼠 H19 ICR 的结构非常相似，但即使在受精后也没有获得印迹性甲基化，这表明转基因片段中缺乏必需的序列。相比之下，在精子发生过程中在内源基因座中获得甲基化的小鼠 IG-DMR 在 TgM 的精子中没有获得甲基化，但在受精后形成的囊胚中高度甲基化，但只有当转基因是父系遗传时才会如此。由于这两个序列是通过采用转基因共定位策略在相同的基因组位点进行评估的，因此这种表型很可能反映了这些片段的内在活性，而不是位置效应的变异性。
我们的结果表明，受精后印迹性甲基化是一种通用的机制，可以保护父系印迹性甲基化在植入前时期免受重新编程。
