Shemer R, Birger Y, Riggs A D, Razin A
Department of Cellular Biochemistry, Hebrew University Hadassah Medical School, P.O. Box 12272, Jerusalem, 91120, Israel.
Proc Natl Acad Sci U S A. 1997 Sep 16;94(19):10267-72. doi: 10.1073/pnas.94.19.10267.
The mouse Snrpn gene encodes the Smn protein, which is involved in RNA splicing. The gene maps to a region in the central part of chromosome 7 that is syntenic to the Prader-Willi/Angelman syndromes (PWS-AS) region on human chromosome 15q11-q13. The mouse gene, like its human counterpart, is imprinted and paternally expressed, primarily in brain and heart. We provide here a detailed description of the structural features and differential methylation pattern of the gene. We have identified a maternally methylated region at the 5' end (DMR1), which correlates inversely with the Snrpn paternal expression. We also describe a region at the 3' end of the gene (DMR2) that is preferentially methylated on the paternal allele. Analysis of Snrpn mRNA levels in a methylase-deficient mouse embryo revealed that maternal methylation of DMR1 may play a role in silencing the maternal allele. Yet both regions, DMR1 and DMR2, inherit the parental-specific methylation profile from the gametes. This methylation pattern is erased in 12.5-days postcoitum (dpc) primordial germ cells and reestablished during gametogenesis. DMR1 is remethylated during oogenesis, whereas DMR2 is remethylated during spermatogenesis. Once established, these methylation patterns are transmitted to the embryo and maintained, protected from methylation changes during embryogenesis and cell differentiation. Transfections of DMR1 and DMR2 into embryonic stem cells and injection into pronuclei of fertilized eggs reveal that embryonic cells lack the capacity to establish anew the differential methylation pattern of Snrpn. That all PWS patients lack DMR1, together with the overall high resemblance of the mouse gene to the human SNRPN, offers an excellent experimental tool to study the regional control of this imprinted chromosomal domain.
小鼠的Snrpn基因编码参与RNA剪接的Smn蛋白。该基因定位于7号染色体中部的一个区域，该区域与人15号染色体q11 - q13上的普拉德 - 威利/安吉尔曼综合征（PWS - AS）区域同线。小鼠基因与其人类对应基因一样，是印记基因且由父本表达，主要在脑和心脏中表达。我们在此详细描述该基因的结构特征和差异甲基化模式。我们在5'端鉴定出一个母本甲基化区域（DMR1），其与Snrpn父本表达呈负相关。我们还描述了该基因3'端的一个区域（DMR2），该区域在父本等位基因上优先甲基化。对甲基化酶缺陷型小鼠胚胎中Snrpn mRNA水平的分析表明，DMR1的母本甲基化可能在沉默母本等位基因中起作用。然而，DMR1和DMR2这两个区域都从配子继承了亲本特异性的甲基化谱。这种甲基化模式在合子后12.5天（dpc）的原始生殖细胞中被消除，并在配子发生过程中重新建立。DMR1在卵子发生过程中重新甲基化，而DMR2在精子发生过程中重新甲基化。一旦建立，这些甲基化模式就会传递给胚胎并维持，在胚胎发育和细胞分化过程中免受甲基化变化的影响。将DMR1和DMR2转染到胚胎干细胞中并注射到受精卵的原核中表明，胚胎细胞缺乏重新建立Snrpn差异甲基化模式的能力。所有普拉德 - 威利综合征患者都缺乏DMR1，再加上小鼠基因与人类SNRPN总体高度相似，这为研究这个印记染色体区域的区域控制提供了一个极好的实验工具。
