HP1γ regulates H3K36 methylation and pluripotency in embryonic stem cells (RNA-seq)

The heterochromatin protein 1 (HP1) family members are canonical effectors and propagators of gene repression mediated by histone H3 lysine 9 (H3K9) methylation. HP1γ exhibits an increased interaction with active transcription elongation-associated factors in embryonic stem cells (ESCs) compared to somatic cells. However, whether this association has a functional consequence remains elusive. Here we find that genic HP1γ colocalizes and enhances enrichment of transcription elongation-associated H3K36me3 rather than H3K9me3. Unexpectedly, sustained H3K36me3 deposition is dependent on HP1γ. HP1γ-deleted ESCs display reduced H3K36me3 enrichment, concomitant with decreased expression at shared genes which function to maintain cellular homeostasis. Both the H3K9me3-binding chromodomain and histone binding ability of HP1γ are dispensable for maintaining H3K36me3 levels. Instead, the chromoshadow together with the hinge domain of HP1γ that confer protein and nucleic acid-binding ability are sufficient because they retain the ability to interact with NSD1, an H3K36 methyltransferase. HP1γ-deleted ESCs have a slower self-renewal rate and an impaired ability to differentiate towards cardiac mesoderm. Our findings reveal a requirement for HP1γ in faithful establishment of transcription elongation in ESCs, which regulates pluripotency. RNA-sequencing of WT or HP1gamma KO ESCs

异染色质蛋白1（heterochromatin protein 1, HP1）家族成员是组蛋白H3赖氨酸9（histone H3 lysine 9, H3K9）甲基化所介导的基因沉默的经典效应因子与传播因子。相较于体细胞，胚胎干细胞（embryonic stem cells, ESCs）中的HP1γ与活跃转录延伸相关因子的相互作用更为增强。然而，这一关联是否存在功能性后果仍未明确。本研究发现，基因区域的HP1γ可与转录延伸相关的H3K36me3（而非H3K9me3）共定位，并增强其富集水平。出乎意料的是，持续的H3K36me3沉积依赖于HP1γ。HP1γ敲除的胚胎干细胞呈现出H3K36me3富集度降低的表型，同时伴随参与维持细胞稳态的共有基因的表达水平下调。HP1γ的H3K9me3结合染色质域（chromodomain）以及组蛋白结合能力，对于维持H3K36me3水平并非必需。取而代之的是，赋予HP1γ蛋白质与核酸结合能力的染色质阴影域（chromoshadow）与铰链结构域（hinge domain）即可发挥相应功能，因为它们能够与H3K36甲基转移酶NSD1产生相互作用。HP1γ敲除的胚胎干细胞自我更新速率减慢，且向心脏中胚层分化的能力受损。本研究结果揭示了HP1γ在胚胎干细胞转录延伸的精准建立过程中的必要性，该过程可调控细胞多能性。野生型（WT）或HP1γ敲除（KO）胚胎干细胞的RNA测序（RNA-sequencing）