KMT5A maintains muscle stem cell quiescence through epigenetic regulation of Notch signaling

Quiescence preserves muscle stem cell (MuSC) identity and regenerative capacity, but the chromatin mechanisms that support this state remain incompletely understood. Here, we show that the H4K20 monomethyltransferase KMT5A sustains canonical Notch signaling in quiescent MuSCs through catalytic deposition of H4K20me1. Loss of Kmt5a led to delayed reduction of Rbpj and other canonical Notch pathway genes, whereas acute catalytic inhibition of KMT5A was sufficient to suppress their expression, indicating that H4K20me1 supports transcriptional competence at Notch loci. Genetic restoration of Notch signaling rescued quiescence-associated features in Kmt5a-deficient MuSCs but did not restore post-activation survival or regenerative output. During physiological activation after injury, H4K20me1 at Notch loci remained largely preserved while H4K20me3 accumulated. Together, these findings identify KMT5A-dependent H4K20me1 as a chromatin mechanism that maintains the Notch-dependent quiescence program and distinguish homeostatic Kmt5a loss from physiological MuSC activation.