Tamada Hiroshi, Van Thuan Nguyen, Reed Peter, Nelson Dominic, Katoku-Kikyo Nobuko, Wudel Justin, Wakayama Teruhiko, Kikyo Nobuaki
Stem Cell Institute, Division of Hematology, Oncology and Transplantation, Department of Medicine, University of Minnesota, MMC 716, 420 Delaware St. SE, Minneapolis, MN 55455, USA.
Mol Cell Biol. 2006 Feb;26(4):1259-71. doi: 10.1128/MCB.26.4.1259-1271.2006.
Somatic cell nuclear cloning has repeatedly demonstrated striking reversibility of epigenetic regulation of cell differentiation. Upon injection into eggs, the donor nuclei exhibit global chromatin decondensation, which might contribute to reprogramming the nuclei by derepressing dormant genes. Decondensation of sperm chromatin in eggs is explained by the replacement of sperm-specific histone variants with egg-type histones by the egg protein nucleoplasmin (Npm). However, little is known about the mechanisms of chromatin decondensation in somatic nuclei that do not contain condensation-specific histone variants. Here we found that Npm could widely decondense chromatin in undifferentiated mouse cells without overt histone exchanges but with specific epigenetic modifications that are relevant to open chromatin structure. These modifications included nucleus-wide multiple histone H3 phosphorylation, acetylation of Lys 14 in histone H3, and release of heterochromatin proteins HP1beta and TIF1beta from the nuclei. The protein kinase inhibitor staurosporine inhibited chromatin decondensation and these epigenetic modifications with the exception of H3 acetylation, potentially linking these chromatin events. At the functional level, Npm pretreatment of mouse nuclei facilitated activation of four oocyte-specific genes from the nuclei injected into Xenopus laevis oocytes. Future molecular elucidation of chromatin decondensation by Npm will significantly contribute to our understanding of the plasticity of cell differentiation.
体细胞核克隆已反复证明细胞分化表观遗传调控具有显著的可逆性。将供体细胞核注入卵母细胞后，其会发生整体染色质解聚，这可能通过解除对休眠基因的抑制来促进细胞核的重编程。卵母细胞中精子染色质的解聚是由卵母细胞蛋白核质蛋白（Npm）将精子特异性组蛋白变体替换为卵母细胞型组蛋白来解释的。然而，对于不含特异性凝聚组蛋白变体的体细胞核中染色质解聚的机制知之甚少。在这里，我们发现Npm可以在未分化的小鼠细胞中广泛地使染色质解聚，而无需明显的组蛋白交换，但会伴随着与开放染色质结构相关的特定表观遗传修饰。这些修饰包括全细胞核范围内的多种组蛋白H3磷酸化、组蛋白H3赖氨酸14位点的乙酰化，以及异染色质蛋白HP1β和TIF1β从细胞核中释放。蛋白激酶抑制剂星形孢菌素抑制了染色质解聚以及除H3乙酰化之外的这些表观遗传修饰，这可能将这些染色质事件联系起来。在功能水平上，对小鼠细胞核进行Npm预处理有助于激活从小鼠细胞核注入非洲爪蟾卵母细胞后所表达的四个卵母细胞特异性基因。未来对Npm介导的染色质解聚进行分子层面的阐释将极大地有助于我们理解细胞分化的可塑性。
