The Histone Variant MacroH2A1 Regulates Key Genes for Myogenic Cell Fusion in a Splice-Isoform Dependent Manner

Abstract

MacroH2A histone variants have functions in differentiation, somatic cell reprogramming and cancer. However, at present, it is not clear how macroH2As affect gene regulation to exert these functions. We have parted from the initial observation that loss of total macroH2A1 led to a change in the morphology of murine myotubes differentiated ex vivo. The fusion of myoblasts to myotubes is a key process in embryonic myogenesis and highly relevant for muscle regeneration after acute or chronic injury. We have focused on this physiological process, to investigate the functions of the two splice isoforms of macroH2A1. Individual perturbation of the two isoforms in myotubes forming in vitro from myogenic C2C12 cells showed an opposing phenotype, with macroH2A1.1 enhancing, and macroH2A1.2 reducing, fusion. Differential regulation of a subset of fusion-related genes encoding components of the extracellular matrix and cell surface receptors for adhesion correlated with these phenotypes. We describe, for the first time, splice isoform-specific phenotypes for the histone variant macroH2A1 in a physiologic process and provide evidence for a novel underlying molecular mechanism of gene regulation.

The histone variant macroH2A1.1 regulates RNA Polymerase II paused genes within defined chromatin interaction landscapes

“…The two first processes were expected based on earlier studies (Kim et al, 2018; Novikov et al, 2011; Judith C Sporn & Jung, 2012; Xu et al, 2012). However, the transcriptional role of mH2A1.1 on cytoskeleton organization and cell adhesion genes is poorly documented except the recent research of Marcus Buschbeck and colleagues showing that mH2A1.1 regulates those categories of genes in murine C2C12 cells (Hurtado-Bagès et al, 2020). Upon transfection of two different siRNA against mH2A1.1, MDA-MB231 cells became more elongated after 2-3 days ( Fig 7A and S16A ).…”

“…Currently, only one study has analyzed transcriptional activities of mH2A1.1 related to its genomic localization, and that is in murine muscle cell line C2C12 (Hurtado-Bagès et al, 2020). As in our study, although mH2A1.1 is mainly implicated in repression of transcription, a significant proportion of genes requires mH2A1.1 for their level of transcription.…”

Epigenetic Regulation of Myogenesis: Focus on the Histone Variants

“…In particular, H3mm7 overexpression positively enhances skeletal muscle gene expression and differentiation in C2C12 cells [ 36 ]. Conversely, deleting H3mm7 by Crispr/Cas9 technology in C2C12 cells leads to the opposite phenotype, i.e., an inhibition of myoblast differentiation [ 37 ]. H3mm7 -null mice are viable and indistinct from the wild type counterparts but muscle regeneration is delayed in these mice [ 37 ].…”

“…Conversely, deleting H3mm7 by Crispr/Cas9 technology in C2C12 cells leads to the opposite phenotype, i.e., an inhibition of myoblast differentiation [ 37 ]. H3mm7 -null mice are viable and indistinct from the wild type counterparts but muscle regeneration is delayed in these mice [ 37 ]. In adult mouse skeletal muscles, H3mm7 is expressed in satellite cells, with a stronger expression associated with the quiescent state, but not in myofibers.…”

“…In adult mouse skeletal muscles, H3mm7 is expressed in satellite cells, with a stronger expression associated with the quiescent state, but not in myofibers. The delay in regeneration of H3mm7 -null mouse muscles is associated with an increased number of embryonic myosin heavy chain (MYH3)-positive fibers, a higher number of fibers with smaller cross-sectional area (CSA), and the downregulation of fiber maturation-related genes [ 37 ]. The number of satellite cells was not affected, which suggests that H3mm7 is dispensable for the maintenance of the stem cell pool but required for myoblast differentiation and maturation.…”