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

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.