Division of Genome Stability Research, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.
Biochem Biophys Res Commun. 2013 Jun 28;436(2):313-8. doi: 10.1016/j.bbrc.2013.05.100. Epub 2013 Jun 4.
Trophoblast lineage differentiation is properly regulated to support embryogenesis. Besides normal developmental process, during germ cell tumor formation or development of other reproductive system diseases, unregulated trophoblast differentiation is also observed and affects the pathogenesis of the diseases. During normal embryogenesis, cell fate of late-stage blastcyst is regulated by a reciprocal repression of the key transcriptional factors; Oct3/4 dominancy inhibits Cdx2 expression in inner cell mass (ICM) and leads them to epiblast/primitive ectoderm but Cdx2 dominancy in trophectoderm (TE) leads them to trophoblast lineage. In contrast during early blastcyst stage, the Cdx2 expression is restricted in TE and not present in ICM, although Oct3/4 signaling does not inhibit the Cdx2 expression in ICM, implying that some factors could be inactivated leading to the suppressed Cdx2 expression in ICM of early blastcyst. ES cells (ESCs), which are derived from ICM, could be a unique model to study trophoblast differentiation in an ectopic context. We previously showed that poly(ADP-ribose) polymerase-1 (Parp-1) deficient ESCs highly expressed non-coding RNA H19 and could differentiate into trophoblast lineage. The expression of H19 is known to start at pre-blastcyst stage during mouse development, and the gene shows high expression only in trophoectoderm (TE) at blastcyst stage. However, its role in trophoblast differentiation has not been clarified yet. Thus, we hypothesized that the H19 activation may act as a trigger for induction of trophoblast differentiation cascade in mouse ESCs. To investigate this issue, we asked whether a forced H19 expression drives ESCs into trophoblast lineage or not. We demonstrated that the H19 induction leads to trophoblast lineage commitment through induction of the Cdx2 expression. We also showed that the expression of Cdx2 is induced in ESCs by forced H19 expression even under a high level of Oct3/4, which could act as a suppressor for Cdx2 expression. It is thus suggested that the H19 induction promotes trophoblast lineage commitment against the repression pressure by Oct3/4 in differentiating ESCs. Taken together, this study suggests that the H19 expression is able to function as a cascade activator of trophoblast lineage commitment possibly by overriding the Oct3/4 action in ESCs.
滋养细胞谱系分化受到适当的调控以支持胚胎发生。除了正常的发育过程外，在生殖细胞肿瘤形成或其他生殖系统疾病发展过程中，也观察到未受调控的滋养细胞分化，这会影响疾病的发病机制。在正常胚胎发生过程中，晚期囊胚的细胞命运由关键转录因子的相互抑制调节；Oct3/4 优势抑制内细胞团（ICM）中的 Cdx2 表达，使其向胚胎外胚层和原始外胚层分化，但在滋养层（TE）中的 Cdx2 优势使其向滋养细胞谱系分化。相反，在早期囊胚阶段，Cdx2 表达局限于 TE 而不存在于 ICM，尽管 Oct3/4 信号不抑制 ICM 中的 Cdx2 表达，但这意味着某些因素可能失活，导致早期囊胚 ICM 中 Cdx2 表达受抑制。ES 细胞（ESCs）来源于 ICM，可作为研究异位滋养细胞分化的独特模型。我们之前曾表明，多聚（ADP-核糖）聚合酶-1（Parp-1）缺陷型 ESCs 高表达非编码 RNA H19，并可分化为滋养细胞谱系。H19 的表达已知在小鼠发育的早期囊胚阶段开始，并且该基因在囊胚阶段仅在滋养外胚层（TE）中高表达。然而，其在滋养细胞分化中的作用尚未阐明。因此，我们假设 H19 的激活可能作为触发小鼠 ESCs 中滋养细胞分化级联的启动子。为了研究这个问题，我们询问强制表达 H19 是否会使 ESCs 分化为滋养细胞谱系。我们证明，通过诱导 Cdx2 的表达，H19 的诱导导致滋养细胞谱系的定向分化。我们还表明，即使在高水平的 Oct3/4 下，强制表达 H19 也会诱导 ESCs 中 Cdx2 的表达。因此，这表明 H19 的诱导促进了滋养细胞谱系的定向分化，对抗了分化 ESCs 中 Oct3/4 的抑制压力。综上所述，这项研究表明，H19 的表达能够作为滋养细胞谱系定向分化的级联激活子发挥作用，可能通过覆盖 ESCs 中的 Oct3/4 作用。
