Abstract
ObjectivesMixed 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.Materials and methodsThe 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.ResultsMLL1 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.ConclusionMLL1 facilitates proliferation of myoblasts and Pax7‐positive satellite cells by epigenetically regulating Myf5 via mediating H3K4me3 on its promoter.
Highlights
Skeletal muscle is a heterogeneous and highly complex tissue that serves a multitude of necessary functions for animal survival.[1]
The process of myoblast specification, proliferation, differentiation and fusion is controlled by many other transcription factors, including sine oculis–related homeobox 4 (Six4),[4] double-sex and mab-3–related transcription factor 2 (Dmrt2),[5] and nuclear factor I X (Nfix).[6]
We explored the expression profile of Mixed lineage leukaemia protein-1 (MLL1) during myoblast differentiation. quantitative PCR (qPCR) and Western blot results demonstrated that MLL1 was highly expressed during C2C12 cell proliferation but gradually decreased after differentiation
Summary
Skeletal muscle is a heterogeneous and highly complex tissue that serves a multitude of necessary functions for animal survival.[1]. Myogenic regulatory factors (MRFs), including Myf[5], myogenin, MyoD and Mrf[4], are key transcription factors that play a central role in transcriptional regulation during muscle formation.[2] During embryonic development, most myogenic cells are derived from dermomyotome. These cells are called progenitors and are marked by high expressions of the paired box transcription factors Pax[3] and Pax7.3 Myf[5] and MyoD are responsible for the specification of. The present study was designed to investigate the roles and regulatory mechanisms of MLL1 in myogenesis
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