Association of mammalian PcG multimeric protein complexes to Hoxb8 gene

为了研究PcG抑制HOX基因表达的分子机制，我们重点研究了PcG蛋白、Rnf2(Ring1b)、Edr1(Rae28/Mph1)、Ring1(Ring1a)和Cbx2(M33)以及组蛋白H3在赖氨酸9(H3K9)上乙酰化后如何与Hoxb8基因侧翼区域结合。在12.5DPC胚胎中，Rnf2与已知的Hoxb8顺式作用调控元件的关联主要发生在HOX基因转录沉默的前胚胎组织中，而Edr1和Cbx2的存在与HOX基因的转录状态无关。相反，H3K9在Hoxb8的乙酰化在胚胎中被发现在尾部增加，与转录活性的分布相一致。这些结果以及整个Hoxb簇中Rnf2结合和H3K9乙酰化的发育概况表明，含有Rnf2的PcG复合体和乙酰化的H3K9的数量相反，可能参与了维持HOX基因表达的前边界。

To address molecular mechanisms underlying Polycomb group (PcG) -mediated repression of Hox gene expression, we have focused on how PcG proteins, Rnf2 (Ring1B), Edr1 (Rae28/Mph1), Ring1 (Ring1A) and Cbx2 (M33), and histone H3 acetylated on lysine 9 (H3K9) bind to flanking regions of the Hoxb8 gene. In 12.5 dpc embryos, association of Rnf2 to known Hoxb8 cis-acting regulatory elements was found predominantly in anterior embryonic tissues where transcription of this Hox gene is silent, whereas the presence of Edr1 and Cbx2 was observed irrespective of Hox transcriptional states. Conversely, acetylation of H3K9 at Hoxb8 was found in caudally increasing amounts in embryos, corresponding with the distribution of transcriptional activity. These results, and the developmental profile of Rnf2 association and H3K9 acetylation across the Hoxb cluster, suggest that inversely graded amounts of Rnf2-containing PcG complex and acetylated H3K9, may be involved in maintaining the anterior boundaries of Hox gene expression.