The Pluripotent Character of Spermatogonial Stem Cells
The pluripotent character of mouse SSCs has been reported by different research teams.[69,70,71] Kanatsu-Shinohara et al were able to derive cells from neonatal mouse testes in vitro, displaying phenotypical similarities to embryonic stem cells (ESCs). These ESC-like cells showed the potency to differentiate into various types of somatic cells in vitro and to induce teratoma formation after injection into nude mice. Furthermore, germline chimeras could be produced after injecting ESC-like cells into blastocysts. Guan et al performed similar experiments with SSCs from adult mice. Adult SSCs generated cells that were able to differentiate in vitro into cell types of all three germ layers and to form teratomas once transplanted in immunodeficient mice. These cells also contributed to the development of various organs after injection into blastocysts.
Similar findings were reported for human SSCs. ESC-like cell lines could be successfully established from adult human SSCs. The cells displayed cellular and molecular characteristics of human ESCs and differentiated into various cell types of the three germ layers.[47,72] However, these results have been put into question. When comparing human adult germline stem cells (GSCs) with human ESCs and human testicular fibroblasts, Ko et al found that the "pluripotent" adult GSCs had a similar gene expression profile to human testicular fibroblasts but different from ESCs. It was reported before that some of the testis-derived cells shared more characteristics with epiblast stem cells than with ESCs.[69,74] This variety in pluripotent states might originate from differences in the derivation protocol.
The debate on the plasticity of SSCs is still ongoing and indicates a need for further characterization of the testis-derived cells before we may have a thorough understanding of their pluripotent potential.
Semin Reprod Med. 2013;31(1):39-48. © 2013 Thieme Medical Publishers