State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, Guangdong, China.
Cell Prolif. 2020 Feb;53(2):e12744. doi: 10.1111/cpr.12744. Epub 2019 Dec 15.
Mixed lineage leukaemia protein-1 (MLL1) mediates histone 3 lysine 4 (H3K4) trimethylation (me3) and plays vital roles during early embryonic development and hematopoiesis. In our previous study, we found its expression was positively correlated with embryonic myogenic ability in pigs, indicating its potential roles in mammalian muscle development. The present work aimed to explore the roles and regulation mechanisms of MLL1 in myogenesis.
The expression of MLL1 in C2C12 cells was experimentally manipulated using small interfering RNAs (siRNA). 5-ethynyl-2'-deoxyuridine (EdU) assay, cell cycle assay, immunofluorescence, qRT-PCR and Western blot were performed to assess myoblast proliferation and differentiation. Chromatin immunoprecipitation assay was conducted to detect H3K4me3 enrichment on myogenic factor 5 (Myf5) promoter. A cardiotoxin (CTX)-mediated muscle regeneration model was used to investigate the effects of MLL1 on myogenesis in vivo.
MLL1 was highly expressed in proliferating C2C12 cells, and expression decreased after differentiation. Knocking down MLL1 suppressed myoblast proliferation and impaired myoblast differentiation. Furthermore, knockdown of MLL1 resulted in the arrest of cell cycle in G1 phase, with decreased expressions of Myf5 and Cyclin D1. Mechanically, MLL1 transcriptionally regulated Myf5 by mediating H3K4me3 on its promoter. In vivo data implied that MLL1 was required for Pax7-positive satellite cell proliferation and muscle repair.
MLL1 facilitates proliferation of myoblasts and Pax7-positive satellite cells by epigenetically regulating Myf5 via mediating H3K4me3 on its promoter.
混合谱系白血病蛋白 1（MLL1）介导组蛋白 3 赖氨酸 4（H3K4）三甲基化（me3），在早期胚胎发育和造血中发挥重要作用。在我们之前的研究中，我们发现其表达与猪胚胎肌生成能力呈正相关，表明其在哺乳动物肌肉发育中具有潜在作用。本研究旨在探索 MLL1 在成肌中的作用和调控机制。
采用小干扰 RNA（siRNA）实验操作 C2C12 细胞中 MLL1 的表达。通过 5-乙炔基-2'-脱氧尿苷（EdU）检测、细胞周期检测、免疫荧光、qRT-PCR 和 Western blot 评估成肌细胞的增殖和分化。采用染色质免疫沉淀实验检测肌生成因子 5（Myf5）启动子上 H3K4me3 的富集情况。利用心肌毒素（CTX）介导的肌肉再生模型研究 MLL1 对体内成肌的影响。
MLL1 在增殖的 C2C12 细胞中高表达，分化后表达降低。敲低 MLL1 抑制成肌细胞增殖并损害成肌细胞分化。此外，敲低 MLL1 导致细胞周期停滞在 G1 期，Myf5 和细胞周期蛋白 D1 的表达减少。机制上，MLL1 通过介导其启动子上的 H3K4me3 转录调控 Myf5。体内数据表明，MLL1 是 Pax7 阳性卫星细胞增殖和肌肉修复所必需的。
MLL1 通过介导其启动子上的 H3K4me3 促进成肌细胞和 Pax7 阳性卫星细胞的增殖，从而促进 Myf5 的表达。
