Precise control of gene expression is fundamental to cell function and development. Although ultimately gene expression relies on DNA-binding transcription factors to guide the activity of the transcription machinery to genes, it has also become clear that chromatin and histone post-translational modification have fundamental roles in gene regulation. Polycomb repressive complexes represent a paradigm of chromatin-based gene regulation in animals. The Polycomb repressive system comprises two central protein complexes, Polycomb repressive complex 1 (PRC1) and PRC2, which are essential for normal gene regulation and development. Our early understanding of Polycomb function relied on studies in simple model organisms, but more recently it has become apparent that this system has expanded and diverged in mammals. Detailed studies are now uncovering the molecular mechanisms that enable mammalian PRC1 and PRC2 to identify their target sites in the genome, communicate through feedback mechanisms to create Polycomb chromatin domains and control transcription to regulate gene expression. In this Review, we discuss and contextualize the emerging principles that define how this fascinating chromatin-based system regulates gene expression in mammals.

基因表达的精确控制是细胞功能和发育的基础。尽管基因表达最终依赖于 DNA 结合转录因子来指导基因转录机制的活动，但染色质和组蛋白翻译后修饰在基因调控中具有重要作用也已变得很清楚。多梳抑制复合物代表了动物中基于染色质的基因调控的范例。 Polycomb 抑制系统包含两个中心蛋白复合物，即 Polycomb 抑制复合物 1 (PRC1) 和 PRC2，它们对于正常基因调控和发育至关重要。我们对 Polycomb 功能的早期理解依赖于对简单模型生物的研究，但最近很明显，这个系统在哺乳动物中已经扩展和分化。目前详细的研究正在揭示使哺乳动物 PRC1 和 PRC2 能够识别其基因组中的靶位点、通过反馈机制进行通信以创建 Polycomb 染色质结构域并控制转录以调节基因表达的分子机制。在这篇综述中，我们讨论并背景化了新兴原理，这些原理定义了这种令人着迷的基于染色质的系统如何调节哺乳动物的基因表达。