Global Center of Excellence Program, Tokyo Medical and Dental University, Tokyo 113-8510, Japan.
Cell Res. 2011 Aug;21(8):1164-71. doi: 10.1038/cr.2011.111. Epub 2011 Jul 12.
Germline stem (GS) cells were established from gonocytes and spermatogonia of postnatal mouse testes. GS cells proliferate in the presence of several kinds of cytokines, and a small percentage of GS cells also show spermatogonial stem cell (SSC) activity, i.e., they differentiate into sperm after being transplanted into infertile mouse testes without endogenous spermatogenesis. Interestingly, in GS cell culture, we also found that pluripotent stem cells (multipotent germline stem cells (mGS cells)) could be derived and these mGS cells do not have normal androgenetic genomic imprinting marks that are shown in GS cells, e.g., H19 hypermethylation. A new culture system for fetal male germ cells (embryonic GS (eGS) cells) has also been recently developed. Although these cells exhibited SSC potential, the offspring from cultured cells showed heritable imprinting defects in their DNA methylation patterns. In an attempt to understand the self-renewal machinery in SSCs, we transfected H-Ras and cylin D2 into GS cells, and successfully reconstructed the SSC self-renewal ability without using exogenous cytokines. Although these cells showed SSC activity in germ cell transplantation assays, we also found development of seminomatous tumors, possibly induced by excessive self-renewing signal. These stem cell culture systems are useful tools not only for understanding the mechanisms of self-renewal or epigenetic reprogramming but also for clarifying the mechanism of germ cell tumor development.
生殖细胞干细胞（GS 细胞）源自出生后小鼠睾丸的精原细胞和精母细胞。GS 细胞在多种细胞因子的存在下增殖，一小部分 GS 细胞也表现出精原干细胞（SSC）的活性，即它们在没有内源性精子发生的情况下被移植到不育小鼠睾丸中后分化为精子。有趣的是，在 GS 细胞培养中，我们还发现可以衍生出多能性干细胞（多能生殖细胞干细胞（mGS 细胞）），并且这些 mGS 细胞没有 GS 细胞中显示的正常雄激素遗传印记标记，例如 H19 超甲基化。最近还开发了一种用于雄性胎儿生殖细胞（胚胎 GS（eGS）细胞）的新培养系统。尽管这些细胞表现出 SSC 潜能，但来自培养细胞的后代在其 DNA 甲基化模式中表现出可遗传的印记缺陷。为了了解 SSCs 中的自我更新机制，我们将 H-Ras 和 cylin D2 转染到 GS 细胞中，成功重建了无需外源细胞因子的 SSC 自我更新能力。尽管这些细胞在生殖细胞移植实验中表现出 SSC 活性，但我们也发现了生殖细胞瘤的发展，这可能是由过度的自我更新信号引起的。这些干细胞培养系统不仅是理解自我更新或表观遗传重编程机制的有用工具，也是阐明生殖细胞肿瘤发展机制的有用工具。
