Spermatogonial stem cells: Progress and prospects

Abstract

Twenty years ago, the transplantation of spermatogonial stem cells (SSCs) from a mouse to other recipient mice was shown to be feasible, which clearly demonstrated the functional identity of SSCs. Since then, several important new findings and other technical developments have followed, which included a new hypothesis on their cell kinetics and spermatogonial hierarchy in the testis, a culture method allowing their self-renewal and proliferation, a testis tissue organ culture method, which induced their complete differentiation up to sperm, and the in vitro induction of germ cells from embryonic stem cells and induced pluripotent stem cells. These advancements reinforced or advanced our understanding of this unique cell. Nonetheless, there are many unresolved questions in the study of spermatogonial stem cells and a long road remains until these cells can be used clinically in reproductive medicine.

Figure 1

Schematic view of the seminiferous epithelium.

Figure 2

Schematic view of self-renewal and differentiation of SSCs. Solid and broken arrows indicate differentiation and self-renewal, respectively.

Figure 3

Schematic view of organ culture and in vitro transplantation of SSCs for in vitro spermatogenesis.

Figure 4

Schematic view of recent progress in the study of in vitro spermatogenesis. In mice, PGC-like cells can be induced from ES and iPS cells under in vitro condition. Transplantation of PGC-like cells into the recipient mouse testis induces their differentiation up to sperm. On the other hand, SSCs can be induced to differentiate into sperm by organ culture in vitro (solid arrows). In future, a therapeutic strategy for infertile patients could be possible through same strategies, especially with in vitro culture method.