Department of Cell and Developmental Biology, University of Illinois, Urbana, IL 61801, USA.
J Cell Biol. 2010 Sep 6;190(5):761-76. doi: 10.1083/jcb.200912167.
Interphase chromatin compaction well above the 30-nm fiber is well documented, but the structural motifs underlying this level of chromatin folding remain unknown. Taking a reductionist approach, we analyzed in mouse embryonic stem (ES) cells and ES-derived fibroblasts and erythroblasts the folding of 10-160-megabase pair engineered chromosome regions consisting of tandem repeats of bacterial artificial chromosomes (BACs) containing approximately 200 kilobases of mammalian genomic DNA tagged with lac operator (LacO) arrays. Unexpectedly, linear mitotic and interphase chromatid regions formed from noncontiguously folded DNA topologies. Particularly, in ES cells, these model chromosome regions self-organized with distant sequences segregating into functionally distinct, compact domains. Transcriptionally active and histone H3K27me3-modified regions positioned toward the engineered chromosome subterritory exterior, with LacO repeats and the BAC vector backbone localizing within an H3K9me3, HP1-enriched core. Differential compaction of Dhfr and alpha- and beta-globin transgenes was superimposed on dramatic, lineage-specific reorganization of large-scale chromatin folding, demonstrating a surprising plasticity of large-scale chromatin organization.
间期染色质的紧密压缩远高于 30nm 纤维已得到充分证实，但这种染色质折叠水平的结构基序仍然未知。采用简化的方法，我们在小鼠胚胎干细胞 (ES) 细胞和 ES 衍生的成纤维细胞和红细胞中分析了由串联重复细菌人工染色体 (BAC) 组成的 10-160Mb 工程染色体区域的折叠，这些 BAC 包含大约 200kb 的带有 lac 操纵子 (LacO) 阵列的哺乳动物基因组 DNA。出乎意料的是，来自非连续折叠 DNA 拓扑结构的有丝分裂和间期染色单体线性区域。特别是在 ES 细胞中，这些模型染色体区域与远距离序列自我组织，这些序列分离成功能不同的、紧密的结构域。转录活性和组蛋白 H3K27me3 修饰区域定位于工程染色体亚域外部，LacO 重复序列和 BAC 载体骨架定位于富含 H3K9me3 和 HP1 的核心内。Dhfr 和 alpha-和 beta-珠蛋白转基因的差异压缩叠加在大规模染色质折叠的显著的、谱系特异性的重排上，证明了大规模染色质组织的惊人的可塑性。
