Expression of the pluripotency marker UTF1 is restricted to a subpopulation of early A spermatogonia in rat testis

The population of early A spermatogonia includes stem cells that possess spermatogonial stern cell properties. Recent reports suggest that these cells have the ability to regain pluripotent properties. Here, we show that expression of the pluripotency marker undifferentiated embryonic cell transcription factor I (UTFI) is restricted to distinct germ cells within the testis. In embryonic and neonatal testes, all gonocytes were found to strongly express UTF1. During further testicular development, expression of UTF I was restricted to a subset of A spermatogonia and with the increase in age the number of cells expressing UTF1 decreased even more. Ultimately, in the adult rat testis, only a smalli subset of the A spermatogonia expressed UTF1. Remarkably, even in testes of vitamin A-deficient rats, in which the early A spermatogonia (A(s), A(pr), and A(al)) are the only type of spermatogonia, only a subset of the spermatogonia expressed UTFI. In the adult rat testis, expression of UTF1 is restricted to a subpopulation of the ZBTBI 6 (PLZF)-positive early A spermatogonia. Furthermore, the observed distribution pattern of UTF1 expressing cells over the different stages of the cycle of the serniniferous epithelium suggests that the expression of UTF1 is restricted to those A(s), A(pr) and short chains of A(al) spermatogonia that are in the undifferentiated state and therefore maintain the ability to differentiate into Al spermatogonia in the next round of the epithelial cycle or possibly even in other directions when they are taken out of their testicular niche.