Polycomb-group proteins are conserved chromatin factors that maintain the silencing of key developmental genes, notably the Hox gene clusters, outside of their expression domains. Depletion of Polycomb repressive complex 1 (PRC1) proteins typically results in chromatin unfolding, as well as ectopic transcription. To disentangle these two phenomena, here we analyze the temporal function of two PRC1 proteins, Polyhomeotic (Ph) and Polycomb (Pc), on Hox gene clusters during Drosophila embryogenesis. We show that the absence of Ph or Pc affects the higher-order chromatin folding of Hox clusters prior to ectopic Hox gene transcription, demonstrating that PRC1 primary function during early embryogenesis is to compact its target chromatin. Moreover, the differential effects of Ph and Pc on Hox cluster folding match the differences in ectopic Hox gene expression observed in these two mutants. Our data suggest that PRC1 maintains gene silencing by folding chromatin domains and impose architectural layer to gene regulation.

中文翻译：

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在果蝇胚胎发生过程中，PRC1 的缺失会诱导 Hox 基因座的高阶开放，而与转录无关。

Polycomb 组蛋白是保守的染色质因子，可在其表达域之外维持关键发育基因的沉默，尤其是 Hox 基因簇。Polycomb 抑制复合物 1 (PRC1) 蛋白的消耗通常会导致染色质展开以及异位转录。为了解开这两种现象，我们在此分析了两种PRC1 蛋白Polyhomeotic (Ph) 和Polycomb (Pc) 在果蝇胚胎发生过程中对Hox 基因簇的时间功能。我们表明，在异位 Hox 基因转录之前，Ph 或 Pc 的缺失会影响 Hox 簇的高阶染色质折叠，这表明早期胚胎发生过程中 PRC1 的主要功能是压缩其靶染色质。而且，Ph 和 Pc 对 Hox 簇折叠的不同影响与在这两个突变体中观察到的异位 Hox 基因表达的差异相匹配。我们的数据表明，PRC1 通过折叠染色质结构域来维持基因沉默，并对基因调控施加结构层。