Fondazione Pasteur Cenci Bolognetti, Section of Histology and Medical Embryology, Department of Anatomical, Histological, Forensic and Orthopaedic Sciences, La Sapienza University of Rome, Via Antonio Scarpa 14, 00161 Rome, Italy.
Reproduction. 2012 Mar;143(3):325-32. doi: 10.1530/REP-11-0385. Epub 2011 Dec 5.
In mice and other mammals, spermatogenesis is maintained by spermatogonial stem cells (SSCs), a cell population belonging to undifferentiated type A spermatogonia. In the accepted model of SSC self-renewal, Asingle (As) spermatogonia are the stem cells, whereas paired (Apaired (Apr)) and chained (Aaligned (Aal)) undifferentiated spermatogonia are committed to differentiation. This model has been recently challenged by evidence that As and chained (Apr and Aal), undifferentiated spermatogonia are heterogeneous in terms of gene expression and function. The expression profile of several markers, such as GFRA1 (the GDNF co-receptor), is heterogeneous among As, Apr and Aal spermatogonia. In this study, we have analysed and quantified the distribution of GFRA1-expressing cells within the different stages of the seminiferous epithelial cycle. We show that in all stages, GFRA1+ chained spermatogonia (Apr to Aal) are more numerous than GFRA1+ As spermatogonia. Numbers of chained GFRA1+ spermatogonia are sharply reduced in stages VII-VIII when Aal differentiate into A1 spermatogonia. GFRA1 expression is regulated by GDNF and in cultures of isolated seminiferous tubules, we found that GDNF expression and secretion by Sertoli cells is stage-dependent, being maximal in stages II-VI and decreasing thereafter. Using qRT-PCR analysis, we found that GDNF regulates the expression of genes such as Tex14, Sohlh1 and Kit (c-Kit) known to be involved in spermatogonial differentiation. Expression of Kit was upregulated by GDNF in a stage-specific manner. Our data indicate that GDNF, besides its crucial role in the self-renewal of stem cells also functions in the differentiation of chained undifferentiated spermatogonia.
在小鼠和其他哺乳动物中，精子发生由精原干细胞（SSC）维持，SSC 是一种属于未分化 A 型精原细胞的细胞群。在公认的 SSC 自我更新模型中，Asingle（As）精原细胞是干细胞，而配对（Apaired（Apr））和链状（Aaligned（Aal））未分化精原细胞则分化。最近有证据表明，As 和链状（Apr 和 Aal）未分化精原细胞在基因表达和功能方面存在异质性，这对该模型提出了挑战。几种标记物（如 GDNF 共受体 GFRA1）的表达谱在 As、Apr 和 Aal 精原细胞中存在异质性。在这项研究中，我们分析并量化了 GFRA1 表达细胞在生精上皮周期不同阶段的分布。我们发现，在所有阶段，GFRA1+链状精原细胞（Apr 到 Aal）的数量都多于 GFRA1+As 精原细胞。当 Aal 分化为 A1 精原细胞时，VII-VIII 期的链状 GFRA1+精原细胞数量急剧减少。GFRA1 的表达受 GDNF 调控，在分离的生精小管培养物中，我们发现 Sertoli 细胞的 GDNF 表达和分泌具有阶段性，在 II-VI 期达到最大值，随后降低。通过 qRT-PCR 分析，我们发现 GDNF 调节基因如 Tex14、Sohlh1 和 Kit（c-Kit）的表达，这些基因已知参与精原细胞分化。GDNF 以阶段特异性方式上调 Kit 的表达。我们的数据表明，GDNF 除了在干细胞自我更新中发挥关键作用外，还在未分化链状精原细胞的分化中发挥作用。
