Human centromeric chromatin is a dynamic chromosomal domain that can spread over noncentromeric DNA
Human centromeric chromatin is a dynamic chromosomal domain that can spread over noncentromeric DNA
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DOI：
10.1073/pnas.0507947103
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发表时间：
2006-03-14
影响因子：
11.1
通讯作者：
Sullivan, BA
中科院分区：
文献类型：
--
作者：
Lam, AL;Boivin, CD;Sullivan, BA
人类着丝粒是含有着丝粒组蛋白 H3 变体 CENP-A 的特殊染色质结构域。 CENP-A 核小体散布着含有在赖氨酸 4 处二甲基化的组蛋白 H3 的核小体，将着丝粒染色质 (CEN 染色质) 与由 H3 赖氨酸 9 甲基化定义的侧翼异染色质区分开来。为了了解染色质组织和人类着丝粒基因组结构之间的关系，我们比较了由不间断的高阶a-卫星DNA定义的三个内源性人类着丝粒的分子谱，与包含不连续的高阶a-卫星DNA和非着丝粒DNA的人类人工染色体。基础序列与染色质状态无关，因为高阶 a-卫星 DNA 和非着丝粒 DNA 都富集了定义 CEN 染色质、常染色质和异染色质的修饰。人类人工染色体也被组织成不同的域。 CENP-A 和异染色质在非着丝粒 DNA（包括杀稻瘟菌素基因）上组装成非重叠结构域。杀稻瘟菌素转录物在 CENP-A 结合位点处富集，但在赖氨酸 9 甲基化的 H3 处不富集，表明在重复 DNA 环境中形成 CEN 染色质并不妨碍基因表达。最后，我们通过增加 CENP-A 剂量来扩展 CEN 结构域，测试了中心异染色质作为着丝粒边界的作用。作为响应，在所有检查的着丝粒中，H3 赖氨酸 9 的二甲基化（而非三甲基化）显着降低。我们认为，人类着丝粒区域通常处于动态状态，其中由 H3 赖氨酸 9 二甲基化定义的区域边界将 CEN 染色质与组成型异染色质分开。
Human centromeres are specialized chromatin domains containing the centromeric histone H3 variant CENP-A. CENP-A nucleosomes are interspersed with nucleosomes containing histone H3 dimethylated at lysine 4, distinguishing centromeric chromatin (CEN chromatin) from flanking heterochromatin that is defined by H3 lysine 9 methylation. To understand the relationship between chromatin organization and the genomic structure of human centromeres, we compared molecular profiles of three endogenous human centromeres, defined by uninterrupted higher-order a-satellite DNA, with human artificial chromosomes that contain discontinuous blocks of higher-order a-satellite DNA and noncentromeric DNA. The underlying sequence did not correlate with chromatin states, because both higher-order a-satellite DNA and noncentromeric DNA were enriched for modifications that define CEN chromatin, euchromatin, and heterochromatin. Human artificial chromosomes were also organized into distinct domains. CENP-A and heterochromatin were assembled over noncentromeric DNA, including the gene blasticidin, into nonoverlapping domains. Blasticidin transcripts were enriched at sites of CENP-A binding but not at H3 methylated at lysine 9, indicating that formation of CEN chromatin within a repetitive DNA environment does not preclude gene expression. Finally, we tested the role of centric heterochromatin as a centromeric boundary by increasing CENP-A dosage to expand the CEN domain. In response, H3 lysine 9 dimethylation, but not trimethylation, was markedly decreased at all centromeres examined. We propose that human centromere regions normally exist in a dynamic state in which a regional boundary, defined by H3 lysine 9 dimethylation, separates CEN chromatin from constitutive heterochromatin.