Short-term in vitro culturing improves transplantability of type A spermatogonia in rainbow trout (Oncorhynchus mykiss)

Continuous production of sperm within the testes is supported by spermatogonial stem cells capable of both self-renewal and the production of numerous differentiated germ cells. We previously demonstrated that a subpopulation of trout type A spermatogonia transplanted into the body cavity of a recipient embryo incorporated into the genital ridge, where they produced functional gametes within the gonads. Various cell-surface proteins could have played a role in the incorporation of spermatogonia into recipient genital ridges. During the preparation of cell suspensions for transplantation in our experimental protocol, however, dissociation of testis by strong proteases was unavoidable. This was problematic as cell-surface proteins may have been at least partially digested by protease activity. In the present study, recovery of spermatogonial surface proteins using short-term culture prior to transplantation was attempted. It was found that spermatogonia cultured in vitro could be harvested by ethylenediaminetetraacetic acid (EDTA) instead of protease treatment. Furthermore, when cultured spermatogonia collected by EDTA treatment were maintained for 24hr in vitro, they exhibited high adhesiveness. These cultured spermatogonia also possessed higher survival of transplantation compared to spermatogonia newly dispersed by trypsin treatment. These results indicated that spermatogonia possess a reduced ability to migrate toward, adhere to, and/or be incorporated into the recipient genital ridge immediately after protease treatment. Short-term in vitro culturing, however, could allow spermatogonia to recover the surface proteins required for successful incorporation into the recipient genital ridge.