Group of Genetics and Epigenetics, de Duve Institute, Université Catholique de Louvain, Brussels, Belgium.
Biochem Biophys Res Commun. 2012 Jan 6;417(1):187-91. doi: 10.1016/j.bbrc.2011.11.120. Epub 2011 Dec 1.
Several human germline-specific genes rely principally on DNA methylation for repression in somatic tissues. Many of these genes, including MAGEA1, were qualified as cancer-germline (CG), as they become activated in tumors, where losses of DNA methylation are common. The developmental stage at which CG genes acquire DNA methylation marks is unknown. Here, we show that in human preimplantation embryos, transcription of CG genes increases up to the morula stage, and then decreases dramatically in blastocysts, suggesting that CG gene silencing occurs in blastocyst stem cells. Consistently, transfection studies with MAGEA1 constructs in embryonal carcinoma (EC) cells, which represent a malignant surrogate of blastocyst-derived stem cells, revealed active repression and marked de novo methylation of MAGEA1 transgenes in these cells. Active repression of the endogenous MAGEA1 gene in human EC cells was evidenced by its rapid re-silencing following prior induction with a DNA methylation inhibitor. Moreover, de novo DNA methyltransferases DNMT3A and DNMT3B appeared to contribute to the silencing of MAGEA1 and other CG genes in EC cells. Altogether our data indicate that CG genes like MAGEA1 are programmed for repression in the blastocyst, and suggest that de novo DNA methylation is a key event in this process.
几个人类种系特异性基因主要依赖于 DNA 甲基化在体细胞组织中被抑制。这些基因中的许多，包括 MAGEA1，被定性为癌症种系（CG），因为它们在肿瘤中被激活，而肿瘤中常见 DNA 甲基化的丢失。CG 基因获得 DNA 甲基化标记的发育阶段尚不清楚。在这里，我们表明在人类胚胎前体中，CG 基因的转录在桑葚胚阶段增加，然后在囊胚中急剧下降，这表明 CG 基因沉默发生在囊胚干细胞中。一致地，用 MAGEA1 构建体转染胚胎癌细胞（EC）的研究表明，这些细胞代表了囊胚衍生的干细胞的恶性替代物，MAGEA1 转基因在这些细胞中被活跃抑制并显著从头甲基化。在人 EC 细胞中，内源性 MAGEA1 基因的活性抑制通过其在 DNA 甲基化抑制剂预先诱导后的快速重新沉默得到证明。此外，新的 DNA 甲基转移酶 DNMT3A 和 DNMT3B 似乎有助于 EC 细胞中 MAGEA1 和其他 CG 基因的沉默。总之，我们的数据表明，像 MAGEA1 这样的 CG 基因在囊胚中被编程为沉默，并且表明从头 DNA 甲基化是该过程中的一个关键事件。
