Mettl1-mediated m(7)G modification of Fgfr2 regulates osteogenic and chondrogenic differentiation of mesenchymal stem cells.

N7-methylguanosine (m(7)G) is a prevalent RNA modification and plays fundamental roles in embryonic stem cell self-renewal and differentiation. However, its specific contributions to mesenchymal stem cell differentiation during skeletal development remain poorly understood. In this study, we demonstrate that specific deletion of the m(7)G methyltransferase Mettl1 in mesenchymal lineage cells causes severe bone development defects, manifesting as dramatic limb shortening at birth. The absence of Mettl1 in mesenchymal stem cells significantly hinders osteoblast and chondrocyte differentiation. Integrative analyses of single-cell RNA-sequencing and m(7)G-MeRIP sequencing demonstrate that Mettl1 ablation disrupts m(7)G modifications of Fgfr2, resulting in reduced its mRNA stability. Fgfr2 downregulation impairs the PI3K-AKT and MAPK signaling pathways, which decreases Sp1 phosphorylation and promotes its ubiquitin-mediated degradation, ultimately leading to reduced transcription of Col1a1 and Col2a1. Pharmacological reactivation of Fgfr2 signaling rescues the defects caused by Mettl1 deletion. Our findings highlight the critical role of Mettl1-mediated m(7)G modification in regulating osteogenic and chondrogenic differentiation of mesenchymal stem cells during bone development and provide new insights into the regulatory mechanisms of RNA modifications in skeletal biology.