Novel epigenetic mechanisms that control pluripotency and quiescence of adult bone marrow-derived Oct4(+) very small embryonic-like stem cells.
Novel epigenetic mechanisms that control pluripotency and quiescence of adult bone marrow-derived Oct4(+) very small embryonic-like stem cells.
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最近，我们在成体组织中发现了一群 Oct4+SSEA-1+Sca-1+lin-CD45-非常小的胚胎样干细胞 (VSEL)。首先，为了解决最近关于从成体器官分离的细胞中 Oct4 表达的争议，我们在此展示了骨髓 (BM) 来源的 VSEL 中的 Oct4 启动子具有开放染色质结构并且活跃转录的证据。接下来，为了解释 VSEL 的静止和畸胎瘤形成的缺乏，我们在一些发育至关重要的印记基因中展示了独特的 DNA 甲基化模式，显示父系甲基化中的印记的低甲基化/擦除和母系甲基化的印记的高甲基化。这些表观遗传特征导致 H19 和 p57KIP2（也称为 Cdkn1c）的 VSEL 上调以及 Igf2 和 Rasgrf1 的抑制，解释了 VSEL 的静止状态。有趣的是，当 VSEL 被诱导形成 VSEL 衍生球体 (VSEL-DS) 时，这种印记基因甲基化的独特模式在与 C2C12 支持细胞系共培养中得到恢复，这些球体富含能够分化为所有三个胚层的干细胞。因此，我们认为Oct4+ VSEL的增殖/发育潜力受到Oct4和一些印记基因的表达的表观遗传调节，并假设恢复印记基因的适当甲基化模式将是在再生医学中使用这些细胞的关键步骤。
Recently, we identified in adult tissues a population of Oct4+SSEA-1+Sca-1+lin-CD45- very small embryonic-like stem cells (VSELs). First, to address recent controversies on Oct4 expression in cells isolated from adult organs we show here an evidence that Oct4 promoter in bone marrow (BM)-derived VSELs has an open chromatin structure and is actively transcribed. Next, to explain VSELs quiescence and lack of teratoma formation we demonstrate a unique DNA methylation pattern at some developmentally crucial, imprinted-genes, showing hypomethylation/erasure of imprints in paternally methylated and hypermethylation of imprints in maternally methylated ones. These epigenetic characteristics leading to upregulation in VSELs of H19 and p57KIP2 (also known as Cdkn1c) and repression of Igf2 and Rasgrf1 explain VSEL's quiescent status. Interestingly, this unique pattern in imprinted-genes methylation is reverted in co-cultures with a C2C12 supportive cell-line when VSELs are induced to form VSEL-derived spheres (VSEL-DSs) enriched for stem cells able to differentiate into all three germ layers. Therefore, we suggest that the proliferative/developmental potential of Oct4+ VSELs is epigenetically regulated by expression of Oct4 and some imprinted-genes, and postulate that restoring the proper methylation pattern of imprinted-genes will be crucial step for employing these cells in regenerative medicine.