G-quadruplex structures are key regulators of mammalian spermatogenesis.

BACKGROUND: Male infertility, impacting 8–12% of couples globally, often lacks clear etiology. G-quadruplexes (G4s), noncanonical DNA structures, are implicated in genomic regulation but remain underexplored in spermatogenesis. This study investigates G4 dynamics and their roles in male fertility. METHODS: We employed antibody-based staining, cleavage under targets and tagmentation (CUT&Tag) sequencing, and a novel nanobody-based proximity labeling system (nanoG4BPL) to map G4 distribution and interacting proteins in mouse testicular cells. In vivo G4 stabilization with pyridostatin and clinical analysis of testicular tissues from patients with nonobstructive azoospermia (NOA) were conducted. RESULTS: G4 structures are enriched in testicular tissues, displaying stage-specific dynamics during spermatogonial differentiation, meiosis, and spermiogenesis. Genome-wide profiling revealed the dual roles of G4s in coordinating gene expression with active epigenetic marks and facilitating genome architecture via CTCF interactions. G4 stabilization disrupted double-strand break repair during meiosis, with nanoG4BPL identifying Nijmegen breakage syndrome 1 (NBS1) as a G4-interacting protein promoting phase separation for homologous recombination. Clinically, patients with NOA exhibited significantly elevated G4 levels in spermatocytes. CONCLUSION: G4 structures are critical regulators of spermatogenesis, orchestrating gene expression, chromatin remodeling, and meiotic fidelity. Their dysregulation, particularly in patients with NOA, suggests a mechanistic link to male infertility, providing novel insights into its pathogenesis and highlighting potential avenues for future diagnostic or therapeutic exploration.