抄録
Mammalians represent a extreme example of sex-divergence in the gamete production: while a human female produce a small number of eggs of around 500, spermatogenesis in male is highly productive and more than 1012 sperms are born during a man's life. This high-throughput spermatogenesis is ensured by a potent stem cell system, while mammalian females seem not depend on obvious stem cell system. The mammalian spermatogenic stem cell system involves a specified microenvironment, the niche, for proper functioning of the stem cells. However, although functionally evidenced, nature of the niche remains mostly unknown. We have previously identified ngn3 (neurogenin3) as a specifically expressed gene in undifferentiated spermatogonia (Aundiff), the small germ stem/progenitor cell population in the mouse testis. GFP labeling allowed the detailed observations of this population without fixation and staining. Adding to that, a time-lapse system has been developed to observe the GFP-positive Aundiff behaviors in the living adult testes. Such observations revealed biased localization of Aundiff with strong relationship to the interstitial cells and blood vessels that surround the tubules. Upon transition into differentiating spermatogonia, they spread out of the restricted original regions to all over the tubules. Finally, alteration of the vasculature pattern is accompanied with the relocation of Aundiff. These observations provides a novel view for the structural basis of the stem cell niche in mammalian spermatogenesis, which may be based on a flexible strategy distinct from organisms with highly polarized gonads. [J Physiol Sci. 2008;58 Suppl:S40]
