Abstract
Malat1 is one of the most abundant long non-coding RNAs in various cell types; its exact cellular function is still a matter of intense investigation. In this study we characterized the function of Malat1 in skeletal muscle cells and muscle regeneration. Utilizing both in vitro and in vivo assays, we demonstrate that Malat1 has a role in regulating gene expression during myogenic differentiation of myoblast cells. Specifically, we found that knockdown of Malat1 accelerates the myogenic differentiation in cultured cells. Consistently, Malat1 knockout mice display enhanced muscle regeneration after injury and deletion of Malat1 in dystrophic mdx mice also improves the muscle regeneration. Mechanistically, in the proliferating myoblasts, Malat1 recruits Suv39h1 to MyoD-binding loci, causing trimethylation of histone 3 lysine 9 (H3K9me3), which suppresses the target gene expression. Upon differentiation, the pro-myogenic miR-181a is increased and targets the nuclear Malat1 transcripts for degradation through Ago2-dependent nuclear RNA-induced silencing complex machinery; the Malat1 decrease subsequently leads to the destabilization of Suv39h1/HP1β/HDAC1-repressive complex and displacement by a Set7-containing activating complex, which allows MyoD trans-activation to occur. Together, our findings identify a regulatory axis of miR-181a-Malat1-MyoD/Suv39h1 in myogenesis and uncover a previously unknown molecular mechanism of Malat1 action in gene regulation.
Highlights
Long non-coding RNAs are emerging as important regulators of gene expression in major biological processes in the nucleus or cytoplasm, having an impact on cell differentiation, stem cell function andIn addition to interacting with proteins, emerging evidence indicates frequent association of MALAT1 with microRNAs
When C2C12 myoblasts were induced to differentiate by switching the cells from proliferation to serumdeprived differentiation medium (DM), according to the published high-throughput RNA-sequencing (RNA-seq) data [41], Malat1 expression was highly expressed in myoblasts and continuously upregulated in a course of 0, 60, 120 and 168 h in DM (Figure 1a and b); this was confirmed by northern blot analysis: a strong signal was detected around 7 kb with the intensity increasing from 0 to 6 days in DM (Figure 1c)
When taking a closer look at the earlier time points of differentiation (o24 h), Malat1 was markedly downregulated at DM 12 h (86% decrease) and 24 h (79% decrease), whereas the early-differentiation marker gene, Myogenin, was continuously induced (Figure 1d and Supplementary Figure S1a and b), suggesting that Malat1 may act as an anti-myogenic factor during the early differentiation of C2C12 myoblasts
Summary
Long non-coding RNAs (lncRNAs) are emerging as important regulators of gene expression in major biological processes in the nucleus or cytoplasm, having an impact on cell differentiation, stem cell function andIn addition to interacting with proteins, emerging evidence indicates frequent association of MALAT1 with microRNAs. Myogenesis, which occurs in both postnatal growth and the regeneration of skeletal muscle after an injury, is a highly ordered process that can be subdivided into multiple steps These steps include the activation of satellite cells (SCs or adult muscle stem cells) into committed myoblasts, followed by proliferation and differentiation of myoblasts, resulting in cell fusion to form myotubes [19, 20]. Owing to the early discovery of the myogenic factors that act downstream, the myoblast differentiation has been extensively studied It is a powerful system for investigating the biological functions of lncRNAs because it can be partially recapitulated in vitro using a C2C12 murine myoblast cell line and because the transcriptional networks coordinating gene expressions are well investigated. The underlying molecular mechanism needs to be further explored and the function of Malat in myogenesis needs further clarification in a regeneration setting in vivo
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