The biology of spermatogonial development in sheep

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Spermatogonial stem cells (stem Sg) are the adult precursors of sperm; their health is critical to propagation of species.  Spermatogonial transplantation is a technique that isolates stem Sg from donor testes and injects them into the seminiferous tubules of a recipient for production of donor sperm by the recipient animal.  Spermatogonial transplantation in mice has proven to be a valuable new tool for studying spermatogenesis, and has opened the possibility of using stem Sg for preservation and dissemination of genetics.  In particular the sheep industry would benefit from additional ways to transport genetics without shipping animals, and from less costly ways to introduce genes directly into the germ line. Rams are a good alternative to rodents for studying post-natal development of spermatogonia in mammals.  They are comparatively small and cheap, and ram lambs are not castrated, so there is a ready supply of testes of all ages from the abattoir for study.  A major problem that must be overcome in studying stem Sg is that they are a minor population in the testis.  Therefore in order to look for molecules important to their health, we will collect individual stem Sg from frozen sections of ram lamb testes with a laser and then extract RNA from the cells to quantify important gene transcripts by PCR.  The RNA also will be used for a broad screening of genes expressed by these cells using microarrays.  The information will be used to increase the efficiency of spermatogonial transplantation in rams.  We also will develop a way to permanently incorporate genes into donor stem Sg using a retrovirus.  Finally we will use spermatogonial transplantation and transduced donor stem Sg to test the function of genes identified in the screens in development of ram spermatogonia.  In the process, we will demonstrate efficiency of spermatogonial transplantation for the farm animal industries and for researchers seeking large animal models of disease.