Biomanipulation of bovine spermatogonial stem cells

The field of spermatogonial stem cell (SSC) technologies provides tools for genetic improvement of cattle herds and multiple opportunities for research. Spermatogonial stems cells belong to the male germ line and as such have high developmental potential, which offers many possibilities for transfer of relevant genetic traits across herds in a timely manner. Type A spermatogonia include a very small number of SSCs and their more numerous differentiating daughter cells. Initial attempts to isolate SSCs started with the isolation of type A spermatogonia and SSC purification. Type A spermatogonia can be obtained in large numbers from young prepubertal bulls, and it is important to note that there are breed differences. Type A spermatogonia isolation can be achieved through mechanical dissociation and enzymatic digestion of the testicular tissue followed by two purification steps, with a final typical bovine type A spermatogonia suspension of 70%. An evaluation for SSC activity using a transplantation assay adapted for bovine SSCs is described. Bovine Type A spermatogonia can be maintained in vitro for short periods (7 to 15 days) with simple culture conditions. However, expansion of SSC can only be achieved under certain conditions such as a specially supplemented medium, specific growth factors, and serial sub-culturing for longer periods of time. After expansion, bovine spermatogonia can be cryopreserved while retaining the ability to proliferate and survive. Despite all the challenges with development of SSC technologies, many questions arise focusing on how bovine SSCs work in a biotechnological setting. Progress in this field will probably result in new applications not only for bulls but also for other species with economical or ecological impact.