DNA G-quadruplex profiling in skeletal muscle stem cells reveals functional and mechanistic insights.

BACKGROUND: DNA G-quadruplexes (G4s) are non-canonical secondary structures formed in guanine-rich DNA sequences and play important roles in modulating biological processes through a variety of gene regulatory mechanisms. Emerging G4 profiling allows global mapping of endogenous G4 formation. RESULTS: Here in this study, we map the G4 landscapes in adult skeletal muscle stem cells (MuSCs), which are essential for injury-induced muscle regeneration. Throughout the myogenic lineage progression of MuSCs, we uncover dynamic endogenous G4 formation with a pronounced G4 induction when MuSCs become activated and proliferating. We further demonstrate that the G4 induction promotes MuSC activation thus the regeneration process. Mechanistically, we found that promoter-associated G4s regulate gene transcription through facilitating chromatin looping. Furthermore, we found that G4 sites are enriched for transcription factor (TF) binding events in activated MuSCs; MAX binds to G4 structures to synergistically facilitate chromatin looping and gene transcription, thus promoting MuSC activation and regeneration. The above uncovered global regulatory functions/mechanisms are further dissected on the paradigm of Ccne1 promoter, demonstrating that Ccne1 is a bona fide G4/MAX regulatory target in activated MuSCs. CONCLUSIONS: Altogether, our findings for the first time demonstrate the prevalent and dynamic formation of G4s in adult MuSCs and the mechanistic role of G4s in modulating gene expression and MuSC activation/proliferation.