The constitutive 20S proteasome is required for the maintenance and differentiation of spermatogonia in mice.

Proteasomes undergo dynamic changes in their types and activities during mammalian spermatogenesis. While the spermatogenesis-specific 20S proteasome (s20S), characterized by PSMA8 substitution of PSMA7, is known to be essential for meiosis I completion, the functions of the constitutive PSMA7-containing 20S proteasomes (c20S) in spermatogenesis remain poorly understood. Here, we show that c20S proteasomes are required for the maintenance and differentiation of spermatogonia. PSMA7 is ubiquitously expressed in male germ cells beginning at the early spermatogonial stage, preceding PSMA8 expression. Conditional ablation of Psma7 using Stra8-Cre impairs proteasomal degradation in differentiating spermatogonia, leading to male infertility. Single-cell RNA sequencing analysis reveals that PSMA7-deleted germ cells are arrested at the differentiating spermatogonia stage and fail to enter meiosis. Notably, sufficient overexpression of PSMA8 restores normal spermatogenesis in Psma7-null germ cells, suggesting a potential complementarity of s20S to c20S. Therefore, our results add critical insights into the complex regulation of proteasomal degradation during spermatogenesis.