Aponte Pedro M, van Bragt Maaike P A, de Rooij Dirk G, van Pelt Ans M M
Department of Endocrinology, Faculty of Biology, Utrecht University, The Netherlands.
APMIS. 2005 Nov-Dec;113(11-12):727-42. doi: 10.1111/j.1600-0463.2005.apm_302.x.
The continuation of the spermatogenic process throughout life relies on a proper regulation of self-renewal and differentiation of the spermatogonial stem cells. These are single cells situated on the basal membrane of the seminiferous epithelium. Only 0.03% of all germ cells are spermatogonial stem cells. They are the only cell type that can repopulate and restore fertility to congenitally infertile recipient mice following transplantation. Although numerous expression markers have been helpful in isolating and enriching spermatogonial stem cells, such as expression of THY-1 and GFRalpha-1 and absence of c-kit, no specific marker for this cell type has yet been identified. Much effort has been put into developing a protocol for the maintenance of spermatogonial cells in vitro. Recently, coculture systems of testicular cells on various feeder cells have made it possible to culture spermatogonial stem cells for a long period of time, as was demonstrated by the transplantation assay. Even expansion of testicular cells, including the spermatogonial stem cells, has been achieved. In these culture systems, hormones and growth factors are investigated for their role in the process of proliferation of spermatogonial stem cells. At the moment the best culture system known still consists of a mixture of testicular cells with about 1.33% spermatogonial stem cells. Recently pure SV40 large T immortalized spermatogonial stem cell lines have been established. These c-kit-negative cell lines did not show any differentiation in vitro or in vivo. A telomerase immortalized c-kit-positive spermatogonial cell line has been established that was able to differentiate in vitro. Spermatocytes and even spermatids were formed. However, spermatogonial stem cell activity by means of the transplantation assay was not tested for this cell line. Both the primary long-term cultures and immortalized cell lines have represented a major step forward in investigating the regulation of spermatogonial self-renewal and differentiation, and will be useful for identifying specific molecular markers.
生精过程在一生中的持续进行依赖于对精原干细胞自我更新和分化的适当调控。这些细胞是位于生精上皮基底膜上的单个细胞。在所有生殖细胞中，精原干细胞仅占0.03%。它们是唯一一种在移植后能够使先天性不育受体小鼠重新繁殖并恢复生育能力的细胞类型。尽管众多表达标志物有助于分离和富集精原干细胞，如THY-1和GFRalpha-1的表达以及c-kit的缺失，但尚未鉴定出针对这种细胞类型的特异性标志物。人们已投入大量精力来开发体外培养精原细胞的方案。最近，在各种饲养细胞上进行睾丸细胞共培养系统已使得长时间培养精原干细胞成为可能，移植试验已证明了这一点。甚至包括精原干细胞在内的睾丸细胞的扩增也已实现。在这些培养系统中，人们研究了激素和生长因子在精原干细胞增殖过程中的作用。目前已知的最佳培养系统仍然是含有约1.33%精原干细胞的睾丸细胞混合物。最近已建立了纯的SV40大T抗原永生化精原干细胞系。这些c-kit阴性细胞系在体外和体内均未表现出任何分化。已建立了一种端粒酶永生化的c-kit阳性精原细胞系，该细胞系能够在体外分化。形成了精母细胞甚至精子细胞。然而，尚未通过移植试验检测该细胞系的精原干细胞活性。原代长期培养物和永生化细胞系在研究精原干细胞自我更新和分化的调控方面都代表了一个重大进展，并且将有助于鉴定特异性分子标志物。
