Polycomb group (PcG) and Trithorax group (TrxG) proteins orchestrate development of a multicellular organism by faithfully maintaining cell fate decisions made early in embryogenesis. An important chromatin mark connected to PcG/TrxG regulation is bivalent domains, the simultaneous presence of H3K27me3 and H3K4me3 on a given locus, originally identified in mammalian embryonic stem cells but considered to be absent in invertebrates. Here, we provide evidence for the existence of bivalency in fly embryos. Using a recently described PcG reporter fly line, we observed a strong reporter inducibility in the embryo and its sharp decrease in larval and adult stages. Analysis of the chromatin landscape of the reporter revealed a strong signal for the repressive PcG mark, H3K27me3, in all three developmental stages and, surprisingly, a strong signal for a transcriptionally activating H3K4me3 mark in the embryo. Using re-chromatin immunoprecipitation experiments, bivalent domains were also uncovered at endogenous PcG targets like the Hox genes.

中文翻译：

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果蝇胚胎中的双亲性与Polycomb靶基因的强诱导性有关。

Polycomb组（PcG）和Trithorax组（TrxG）蛋白通过忠实地维持胚胎发生早期做出的细胞命运决定，来协调多细胞生物的发育。与PcG / TrxG调控相关的重要染色质标记是二价域，即在给定的基因座上同时存在H3K27me3和H3K4me3，最初是在哺乳动物胚胎干细胞中鉴定出来的，但在无脊椎动物中不存在。在这里，我们提供了蝇胚胎中双价存在的证据。使用最近描述的PcG记者飞行路线，我们观察到了在胚胎中很强的记者可诱导性，并且在幼虫和成年阶段它的急剧减少。对记者染色质分布的分析显示，在所有三个发育阶段中，抑制性PcG标记H3K27me3均具有强烈信号，令人惊讶的是，在胚胎中转录激活H3K4me3标记的强信号。使用重染色质免疫沉淀实验，还在内源性PcG靶标（如Hox基因）上发现了二价域。