Proteomics and single-cell RNA analysis of Akap4-knockout mice model confirm indispensable role of Akap4 in spermatogenesis

Sperm fibrous sheath, a unique cytoskeletal structure, is implicated in various sperm physiological functions, such as sperm maturation, motility and capacitation. AKAP4 has been described to be required for structural and functional integrity of the fibrous sheath. We generated Akap4-knockout mice line using CRISPR-Cas9 system. Cytomorphology and motility of sperm and testes were studied, confirming loss of Akap4 led to abnormal sperm morphology, motility and infertility. The proteomic components of testes were studied and Akap4 was found to be significantly decreased in the Akap4-knockout mice. Testis single-cell RNA sequencing and analysis revealed three genes with significant change in the general cell population, i.e., Akap4, Haspin, and Ccdc38. The single-cell RNA expression profiles also showed that the major difference between Akap4-knockout and wild-type testes existed in the elongating cell cluster, where in the Akap4-knockout testes, a subgroup of elongating cells with marker genes involved in cell adhesion and migration were increased, while a subgroup of elongating cells marked by mitochondrial sheath genes were decreased. Our results revealed the complex and well-coordinated procedures of spermatogenesis, and substantiated Akap4's indispensable roles in the integrity of sperm flagellum and the step-wise maturation of spermatozoa.