Id4 Marks Spermatogonial Stem Cells in the Mouse Testis

AbstractMammalian spermatogenesis is a classic adult stems cell–dependent process, supported by the self-renewal and differentiation of spermatogonial stem cells (SSCs). However, the identification of SSCs and elucidation of their behaviors in undisturbed testis has long been a big challenge. Here, we generated a knock-in mouse model, Id4-2A-CreERT2-2A-tdTomato, which allowed us to mark Id4-expressing (Id4+) cells at different time pointsin situand track their behaviors across distinct developmental stages during steady-state and regenerating spermatogenesis. We found that Id4+cells continue to produce spermatogonia, spermatocytes and sperm in mouse testis, showing they are capable of self-renewal and have differentiation potential. Consistent with these findings, ablation of Id4+cells in mice results in a loss of spermatogenesis. Furthermore, developmental fate mapping reveals that Id4+SSCs originate from neonate Id4+gonocytes. Therefore, our results indicate that Id4 marks spermatogonial stem cells in the mouse testis.