Lin28a forms an RNA‐binding complex with Igf2bp3 to regulate m6A‐modified stress response genes in stress granules of muscle stem cells

Abstract

AbstractIn the early embryonic stages, Lin‐28 homologue A (Lin28a) is highly expressed and declines as the embryo matures. As an RNA‐binding protein, Lin28a maintains some adult muscle stem cells (MuSCs) in an embryonic‐like state, but its RNA metabolism regulation mechanism remains unclear. BioGPS analysis revealed that Lin28a expression is significantly higher in muscle tissues than in other tissues. Lin28a‐positive muscle stem cells (Lin28a+ MuSCs) were sorted from Lin28a‐CreERT2; LSL‐tdTomato mouse skeletal muscle tissue, which exhibited a higher proliferation rate than the control group. Lin28a‐bound transcripts are enriched in various biological processes such as DNA repair, cell cycle, mitochondrial tricarboxylic acid cycle and oxidative stress response. The expression of insulin‐like growth factor 2 mRNA‐binding protein 3 (Igf2bp3) was markedly elevated in the presence of Lin28a. Co‐immunoprecipitation analysis further demonstrated that Lin28a associates with Igf2bp3. Immunofluorescence analyses confirmed that Lin28a, Igf2bp3 and G3bp1 colocalize to form stress granules (SG), and N6‐methyladenosine (m6A) modification promotes the formation of Lin28a‐SG. Sequencing of the transcriptome and RNAs immunoprecipitated by Lin28a, Igf2bp3 and m6A antibodies in Lin28a+ MuSCs further revealed that Lin28a and Igf2bp3 collaboratively regulate the expression of DNA repair‐related genes, including Fancm and Usp1. Lin28a stabilises Igf2bp3, Usp1, and Fancm mRNAs, enhancing DNA repair against oxidative or proteotoxic stress, thus promoting MuSCs self‐renewal. Understanding the intricate mechanisms through which Lin28a and Igf2bp3 regulate MuSCs provides a deeper understanding of stem cell self‐renewal, with potential implications for regenerative medicine.