Spermatogonial stem cell
Type B spermatogonia, on the other hand, differentiate into spermatocytes, which in turn undergo meiosis to eventually form mature sperm cells.
[21] Cells present in the testes express molecules that play key roles in the regulation of SSC self-renewal.
SSCs survive within microenvironments, termed niches, which provide extrinsic stimuli that drive stem cell differentiation or self-renewal.
[24] The SSC niche is found in the seminiferous epithelium of mammalian testis and is primarily constituted of Sertoli and peritubular myoid cells.
[26] SSCs have the potential to become increasingly clinically relevant in treating sterility (in vitro spermatogenesis) and preserving fertility before gonadotoxic treatments.
Once isolated, SSC populations are cultured for amplification, characterization, line maintenance, and potentially in vitro spermatogenesis or genomic editing.
[30] The main challenges to SSC culturing are the interactions between media substances and the epigenetic makeup that underlies pluripotency and can affect future offspring.
[31] The long-term culture of human SSCs is not established yet, however, one group reports successful proliferation in feeder cell-free media supplied with growth factors and hydrogel.
[33] These mice were then able to produce viable offspring which opened new exciting doors for future potential therapies in humans.
[34] Spermatogonial stem cell therapy (SSCT) has been proposed as a potential method to restore fertility in cancer survivors who desire to have children later in life.
The method has been tested in numerous animal models including non-human primates; Hermann et al.[35] took out and isolated SSCs from prepubertal and adult rhesus macaques before treating them with busulfan (an alkylating agent used in chemotherapy).
SSCs were then injected back into the rete testis of the same animal that they were taken from ~10–12 weeks after treatment, and spermatogenesis was observed in almost all recipients (16/17).
The viability of embryos fertilized by donor sperm after SSC transplantation needs to be evaluated to truly determine the usefulness of this technique.
Roe et al. [36] suggested that the reproductive lifespan of such species could be extended by transplanting their germ cells into a domestic host.
This allows the isolation of mature sperm later on in development from the host even after the donor has deceased which can be used in future fertilization and potentially more successful conservation.
