Izadyar Fariborz, Pau Francis, Marh Joel, Slepko Natalia, Wang Tracy, Gonzalez Rafael, Ramos Thomas, Howerton Kyle, Sayre Chauncey, Silva Francisco
PrimeGen Biotech LLC, 213 Technology Drive, Irvine, California 92618, USA.
Reproduction. 2008 Jun;135(6):771-84. doi: 10.1530/REP-07-0479.
Spermatogonial stem cells (SSCs) maintain spermatogenesis by self-renewal and generation of spermatogonia committed to differentiation. Under certain in vitro conditions, SSCs from both neonatal and adult mouse testis can reportedly generate multipotent germ cell (mGC) lines that have characteristics and differentiation potential similar to embryonic stem (ES) cells. However, mGCs generated in different laboratories showed different germ cell characteristics, i.e., some retain their SSC properties and some have lost them completely. This raises an important question: whether mGC lines have been generated from different subpopulations in the mouse testes. To unambiguously identify and track germ line stem cells, we utilized a transgenic mouse model expressing green fluorescence protein under the control of a germ cell-specific Pou5f1 (Oct4) promoter. We found two distinct populations among the germ line stem cells with regard to their expression of transcription factor Pou5f1 and c-Kit receptor. Only the POU5F1+/c-Kit+ subset of mouse germ line stem cells, when isolated from either neonatal or adult testes and cultured in a complex mixture of growth factors, generates cell lines that express pluripotent ES markers, i.e., Pou5f1, Nanog, Sox2, Rex1, Dppa5, SSEA-1, and alkaline phosphatase, exhibit high telomerase activity, and differentiate into multiple lineages, including beating cardiomyocytes, neural cells, and chondrocytes. These data clearly show the existence of two distinct populations within germ line stem cells: one destined to become SSC and the other with the ability to generate multipotent cell lines with some pluripotent characteristics. These findings raise interesting questions about the relativity of pluripotency and the plasticity of germ line stem cells.
精原干细胞（SSCs）通过自我更新和产生致力于分化的精原细胞来维持精子发生。据报道，在某些体外条件下，来自新生和成年小鼠睾丸的SSCs能够产生具有与胚胎干细胞（ES）相似特征和分化潜能的多能生殖细胞（mGC）系。然而，不同实验室产生的mGCs表现出不同的生殖细胞特征，即一些保留了它们的SSC特性，而一些则完全丧失了这些特性。这就提出了一个重要问题：mGC系是否是从小鼠睾丸中的不同亚群产生的。为了明确识别和追踪生殖系干细胞，我们利用了一种在生殖细胞特异性Pou5f1（Oct4）启动子控制下表达绿色荧光蛋白的转基因小鼠模型。我们发现，在生殖系干细胞中，就转录因子Pou5f1和c-Kit受体的表达而言，存在两个不同的群体。只有小鼠生殖系干细胞的POU5F1+/c-Kit+亚群，当从新生或成年睾丸中分离出来并在生长因子的复杂混合物中培养时，才能产生表达多能ES标记物（即Pou5f1、Nanog、Sox2、Rex1、Dppa5、SSEA-1和碱性磷酸酶）的细胞系，表现出高端粒酶活性，并分化为多个谱系，包括跳动的心肌细胞、神经细胞和软骨细胞。这些数据清楚地表明，生殖系干细胞中存在两个不同的群体：一个注定成为SSC，另一个具有产生具有一些多能特性的多能细胞系的能力。这些发现提出了关于多能性的相对性和生殖系干细胞可塑性的有趣问题。
