RPS27L Enhances Myogenesis and Muscle Mass by Targeting IGF1 Through Liquid‐Liquid Phase Separation

Abstract RNA‐binding proteins (RBPs) play a pivotal role in post‐transcriptional regulation of gene expression, critically influencing skeletal myogenesis, muscle growth, and regeneration. Despite the recent identification of RBP Rps27l (ribosomal protein S27‐like) as a regulator affecting myogenic proliferation and differentiation, its functions and regulatory mechanisms in skeletal muscle development remain largely unknown. In this study, it is observed that muscle‐specific Rps27l knock‐in (M─KI) mice exhibit significantly increased muscle mass, enlarged myofiber size, a higher proportion of fast‐twitch myofibers, and enhanced muscle regeneration capabilities compared to wild‐type controls. Overexpression of Rps27l promotes myoblast proliferation while inhibiting differentiation in skeletal muscle cells. Mechanistically, it is revealed that the expression of Rps27l is negatively regulated by SIX4, a myogenic transcription factor. The N‐terminal intrinsically disordered region of RPS27L facilitates liquid‐liquid phase separation (LLPS) and interacts with IGF1 to collaboratively regulate myogenesis. The findings uncover the novel regulatory roles of RPS27L in skeletal muscle and highlight the significance of RPS27L‐driven LLPS in myogenesis.