Mouse spermatogenesis is supported by spermatogenic stem cells (SSCs). SSCs maintain their pool while migrating over an open (or facultative) niche microenvironment of testicular seminiferous tubules, where ligands that support self-renewal are likely distributed widely. This contrasts with the classic picture of closed (or definitive) niches in which stem cells are gathered and the ligands are highly localized. Some of the key properties observed in the dynamics of SSCs in the testicular niche in vivo, which show the flexible and stochastic (probabilistic) fate behaviors, are found to be generic for a wide range of, if not all, tissue stem cells. SSCs also show properties characteristic of an open niche-supported system, such as high motility. Motivated by the properties of SSCs, in this review, I will reconsider the potential unity and diversity of tissue stem cell systems, with an emphasis on the varying degrees of ligand distribution and stem cell motility.

中文翻译：

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小鼠精子发生反映了组织干细胞生态位系统的统一性和多样性

生精干细胞 (SSC) 支持小鼠精子发生。SSC 在睾丸曲细精管的开放（或兼性）生态位微环境中迁移时维持其池，支持自我更新的配体可能分布广泛。这与封闭（或最终）生态位的经典图片形成对比，在这些生态位中聚集了干细胞并且配体高度定位。在体内睾丸生态位的 SSC 动力学中观察到的一些关键特性显示出灵活和随机（概率）的命运行为，被发现对于广泛的（如果不是全部）组织干细胞是通用的。SSC 还显示出开放利基支持系统的特性，例如高机动性。受 SSC 特性的启发，在这篇综述中，