Analysis of spermatogonial proliferation with technique of spermatogonial transplantation-A trial for improving spermatogenic activity

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Spermatogonial transplantation has several unique advantages when applied to the study of spermatogenesis. For instance, germ cells and testis environment composed of many somatic cells can be differently treated to see effects of the treatments. The proliferation status of spermatogonia can be also clearly observed in the early stage of colony development after transplantation. We have first introduced GFP mice in this system as donor mice by which the system became more quantitative. With GFP mice as donor, sequential transplantation of spermatogonial stem cell became possible. We have so far succeeded to passage stem cells for 4 times successively. Accumulated data indicated that spermatogonial stem cells expand as colony size increases, and as time passes by. The expansion rate was estimated to be about 30-fold during 100 days following transplantation. This expansion rate appeared to be constant for more than a year showing no sign of exhaustion. Meanwhile, we also tried to find the effect of intra-testicular microenvironment on spermatogonial proliferation. The LH-RH analogue (leuprorelin) was used to modify hormonal environment of the testis. In the leuprorelin-treated mouse testes, transplanted speramtogonia presented more densely on the basement membrane of the seminiferous tubules as early as 4 weeks after the transplantation. This finding suggests that spermatogonia are stimulated to proliferate or their apoptosis are reduced in the leuprorelin-treated mouse testes. Our present research established the spermatogonial transplantation technique as a quantitative method for evaluating various treatments on spermatogonial proliferation, differentiation, and death.