Only a small population of adult Sertoli cells actively proliferates in culture.

Adult mammalian Sertoli cells (SCs) have been considered to be quiescent terminal differentiated cells for many years, but recently, proliferation of adult SCs was demonstrated in vitro and in vivo We further examined mouse SC behavior in culture and found that there are two populations of adult SCs. The first population is SCs from seminiferous tubules that hardly proliferate in vitro The second population is small and consists of SCs with atypical nuclear morphology from the terminal segments of seminiferous tubules, a transitional zone (TZ). TZ SCs multiply in culture and form colonies, display mixture of mature and immature SC characteristics, and generate cord-like structures in a collagen matrix. The specific features of TZ SCs are ACTA2 expression in vitro and DMRT1 low levels in vivo and in vitro Although the in vivo function of TZ SCs still remains unclear, this finding has significant implications for our understanding of SC differentiation and functioning in adult mammals.