The nuclear architecture of rod photoreceptor cells in nocturnal mammals is unlike that of other animal cells. Murine rod cells have an “inverted” chromatin organization with euchromatin at the nuclear periphery and heterochromatin packed in the center of the nucleus. In conventional nuclear architecture, euchromatin is mostly in the interior, and heterochromatin is largely at the nuclear periphery. We demonstrate that inverted nuclear architecture is achieved through global relabeling of the rod cell epigenome. During rod cell maturation, H3K9me2-labeled nuclear peripheral heterochromatin is relabeled with H3K9me3 and repositioned to the nuclear center, while transcriptionally active euchromatin is labeled with H3K9me2 and positioned at the nuclear periphery. Global chromatin relabeling is correlated with spatial rearrangement, suggesting a critical role for histone modifications, specifically H3K9 methylation, in nuclear architecture. These results reveal a dramatic example of genome-wide epigenetic relabeling of chromatin that accompanies altered nuclear architecture in a postnatal, postmitotic cell.

中文翻译：

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全局染色质重新标记伴随视杆细胞中染色质的空间倒置

夜间哺乳动物视杆细胞的核结构不同于其他动物细胞。鼠视杆细胞具有“倒置”的染色质组织，常染色质位于核外围，异染色质位于细胞核中心。在传统的核结构中，常染色质主要位于内部，异染色质主要位于核外围。我们证明了倒置的核结构是通过对杆状细胞表观基因组进行全局重新标记来实现的。在视杆细胞成熟过程中，H3K9me2 标记的核外周异染色质被 H3K9me3 重新标记并重新定位到核中心，而转录活性常染色质被 H3K9me2 标记并定位在核外周。全局染色质重新标记与空间重排相关，表明组蛋白修饰，特别是 H3K9 甲基化在核结构中的关键作用。这些结果揭示了染色质全基因组表观遗传重新标记的一个引人注目的例子，它伴随着出生后有丝分裂后细胞中核结构的改变。