MAP7-driven cytoskeletal cross-talk establishes Sertoli cell polarity crucial for germ cell meiotic progression

Abstract

How specialized apical membrane domains are assembled in vivo remains poorly understood. In the mouse testis, Sertoli cells build a luminal apical domain after birth that organizes the seminiferous epithelium and supports germ cell differentiation, distinct from fetal polarity established during cord formation. Here, we identify the microtubule-associated protein MAP7 as a key regulator of cytoskeletal organization during apical domain formation. MAP7 preferentially localizes to apical microtubules in Sertoli cells, showing limited overlap with stable microtubule markers. Native-tissue imaging indicates that MAP7-decorated microtubules, initially lacking obvious directionality, become increasingly aligned along the tubule axis as the apical domain matures. In Map7-deficient testes, microtubule abundance is maintained, but higher-order organization is disrupted and accompanied by persistent luminal F-actin accumulation. These defects compromise apical domain maturation and lumen formation during the first wave of spermatogenesis and are associated with altered tight-junction patterning. Proteomic analysis identifies the non-muscle myosin II heavy chains MYH9 and MYH10 among MAP7-associated proteins. MYH9 becomes enriched at luminal regions where microtubules and F-actin converge, but remains diffuse in Map7-deficient Sertoli cells despite ectopic luminal cytoskeletal assemblies, suggesting that MAP7 helps establish a cytoskeletal context that supports spatially restricted NMII enrichment. Single-cell RNA sequencing shows that Sertoli transcriptional differentiation largely proceeds without MAP7, whereas germ cells exhibit delayed meiotic progression with expansion of pachytene-stage subpopulations. Together, these findings establish MAP7-dependent microtubule remodeling as an organizing mechanism for postnatal apical domain maturation and suggest how epithelial cytoskeletal architecture shapes a niche that helps pace developmental progression of neighboring germ cells.