Decoding Spermatogenesis: The Pivotal Role of Protein Phosphorylation in Male Fertility

Protein phosphorylation is a rapid, reversible post-translational modification that plays a central role in mammalian spermatogenesis and sperm functional maturation. This review integrates evidence from phosphoproteomics, genetics, and functional studies to summarize how phosphorylation networks govern key steps of germ-cell development. We outline how major kinases and phosphatases – including the testis-specific serine/threonine kinases (TSSKs), Polo-like kinases (PLKs), IGF1R tyrosine kinase, metabolic kinases (AMPK, AK9, GK2), tyrosine kinases (C-kit, TAM family: TYRO3, AXL, MER), and the PP2A/PP1 phosphatases – coordinate spermatogonial proliferation and differentiation, meiotic chromosome dynamics, spermiogenesis, and post-epididymal capacitation. Metabolic kinases bridge phosphorylation signaling with energy metabolism to support sperm motility, while C-kit and TAM family kinases regulate germ cell maturation and Sertoli cell homeostasis (e.g., blood-testis barrier integrity, phagocytosis of apoptotic germ cells). We also highlight extensive crosstalk between phosphorylation and other regulatory layers, particularly histone modifications and ubiquitination, which together form an integrated network required for normal sperm development and function. Recent advances in mass spectrometry–based phosphoproteomics – especially DIA/SWATH-MS and emerging single-cell phosphoproteomic approaches – have enabled stage-resolved, system-level maps of phosphorylation dynamics, revealing critical sites and pathways that define specific developmental transitions. Importantly, disruption of these networks (including aberrant activity of metabolic kinases and tyrosine kinases) is closely associated with male infertility phenotypes, including oligozoospermia, asthenozoospermia, teratozoospermia, and increased sperm DNA fragmentation, supporting the use of phosphorylation signatures and kinase/phosphatase expression patterns as candidate diagnostic biomarkers. Finally, we propose a “mechanism–technology–clinical” research framework that combines spatiotemporally resolved phosphoproteomics, epigenetic interaction analyses, and AI-assisted network inference to define causal phosphorylation circuits. Prioritizing key regulatory nodes – such as the TSSK family, AKAP proteins, metabolic kinases, and TAM/C-kit tyrosine kinases – may accelerate the development of phosphorylation-based diagnostics and enable non-hormonal strategies for male contraception and fertility restoration. Overall, this review provides a unified view of how phosphorylation, integrating metabolic and tyrosine kinase signaling, shapes sperm development and function and offers direction for translational research in male reproductive health.