Butler John T, Hall Lisa L, Smith Kelly P, Lawrence Jeanne B
Department of Cell Biology, University of Massachusetts Medical School, Worcester, 01655, USA.
J Cell Biochem. 2009 Jul 1;107(4):609-21. doi: 10.1002/jcb.22183.
The complex nuclear structure of somatic cells is important to epigenomic regulation, yet little is known about nuclear organization of human embryonic stem cells (hESC). Here we surveyed several nuclear structures in pluripotent and transitioning hESC. Observations of centromeres, telomeres, SC35 speckles, Cajal Bodies, lamin A/C and emerin, nuclear shape and size demonstrate a very different "nuclear landscape" in hESC. This landscape is remodeled during a brief transitional window, concomitant with or just prior to differentiation onset. Notably, hESC initially contain abundant signal for spliceosome assembly factor, SC35, but lack discrete SC35 domains; these form as cells begin to specialize, likely reflecting cell-type specific genomic organization. Concomitantly, nuclear size increases and shape changes as lamin A/C and emerin incorporate into the lamina. During this brief window, hESC exhibit dramatically different PML-defined structures, which in somatic cells are linked to gene regulation and cancer. Unlike the numerous, spherical somatic PML bodies, hES cells often display approximately 1-3 large PML structures of two morphological types: long linear "rods" or elaborate "rosettes", which lack substantial SUMO-1, Daxx, and Sp100. These occur primarily between Day 0-2 of differentiation and become rare thereafter. PML rods may be "taut" between other structures, such as centromeres, but clearly show some relationship with the lamina, where PML often abuts or fills a "gap" in early lamin A/C staining. Findings demonstrate that pluripotent hES cells have a markedly different overall nuclear architecture, remodeling of which is linked to early epigenomic programming and involves formation of unique PML-defined structures.
体细胞复杂的核结构对表观基因组调控很重要，但对于人类胚胎干细胞（hESC）的核组织却知之甚少。在这里，我们研究了多能性和正在转变的hESC中的几种核结构。对着丝粒、端粒、SC35斑点、卡哈尔体、核纤层蛋白A/C和emerin、核形状和大小的观察表明，hESC中存在非常不同的“核景观”。这种景观在一个短暂的过渡窗口期间重塑，与分化开始同时或就在分化开始之前。值得注意的是，hESC最初含有丰富的剪接体组装因子SC35信号，但缺乏离散的SC35结构域；这些结构域在细胞开始特化时形成，可能反映了细胞类型特异性的基因组组织。与此同时，随着核纤层蛋白A/C和emerin整合到核纤层中，核大小增加且形状改变。在这个短暂的窗口期间，hESC表现出截然不同的由早幼粒细胞白血病（PML）定义的结构，而在体细胞中这些结构与基因调控和癌症有关。与众多球形的体细胞PML小体不同，hES细胞通常显示大约1 - 3个两种形态类型的大PML结构：长线性“杆状”或精致的“玫瑰花结”，它们缺乏大量的小泛素样修饰蛋白1（SUMO - 1）、死亡结构域相关蛋白（Daxx）和Sp100。这些结构主要出现在分化的第0 - 2天之间，此后变得罕见。PML杆状结构可能在其他结构（如着丝粒）之间“拉紧”，但明显显示出与核纤层有某种关系，在早期核纤层蛋白A/C染色中，PML常常邻接或填充一个“间隙”。研究结果表明，多能性hES细胞具有明显不同的整体核结构，其重塑与早期表观基因组编程相关，并涉及独特的由PML定义的结构的形成。
