Ohmura Masako, Naka Kazuhito, Hoshii Takayuki, Muraguchi Teruyuki, Shugo Haruhiko, Tamase Akira, Uema Noriyuki, Ooshio Takako, Arai Fumio, Takubo Keiyo, Nagamatsu Go, Hamaguchi Isao, Takagi Minoru, Ishihara Masahiko, Sakurada Kazuhiro, Miyaji Hiromasa, Suda Toshio, Hirao Atsushi
Division of Molecular Genetics, Center for Cancer and Stem Cell Research, Cancer Research Institute, Kanazawa University, Kanazawa, Ishikawa, Japan.
Stem Cells. 2008 Dec;26(12):3237-46. doi: 10.1634/stemcells.2008-0506. Epub 2008 Sep 18.
The nucleostemin (NS) gene encodes a nucleolar protein found at high levels in several types of stem cells and tumor cell lines. The function of NS is unclear but it may play a critical role in S-phase entry by stem/progenitor cells. Here we characterize NS expression in murine male germ cells. Although NS protein was highly expressed in the nucleoli of all primordial germ cells, only a limited number of gonocytes showed NS expression in neonatal testes. In adult testes, NS protein was expressed at high levels in the nucleoli of spermatogonia and primary spermatocytes but at only low levels in round spermatids. To evaluate the properties of cells expressing high levels of NS, we generated transgenic reporter mice expressing green fluorescent protein (GFP) under the control of the NS promoter (NS-GFP Tg mice). In adult NS-GFP Tg testes, GFP and endogenous NS protein expression were correlated in spermatogonia and spermatocytes but GFP was also ectopically expressed in elongated spermatids and sperm. In testes of NS-GFP Tg embryos, neonates, and 10-day-old pups, however, GFP expression closely coincided with endogenous NS expression in developing germ cells. In contrast to a previous report, our results support the existence in neonatal testes of spermatogonial stem cells with long-term repopulating capacity. Furthermore, our data show that NS expression does not correlate with cell-cycle status during prepuberty, and that strong NS expression is essential for the maintenance of germline stem cell proliferation capacity. We conclude that NS is a marker of undifferentiated status in the germ cell lineage during prepubertal spermatogenesis.
核仁素（NS）基因编码一种核仁蛋白，该蛋白在多种类型的干细胞和肿瘤细胞系中高水平表达。NS的功能尚不清楚，但它可能在干细胞/祖细胞进入S期过程中起关键作用。在此，我们对小鼠雄性生殖细胞中NS的表达进行了表征。尽管NS蛋白在所有原始生殖细胞的核仁中高度表达，但在新生睾丸中只有有限数量的生殖母细胞显示出NS表达。在成年睾丸中，NS蛋白在精原细胞和初级精母细胞的核仁中高水平表达，但在圆形精子细胞中仅低水平表达。为了评估高水平表达NS的细胞的特性，我们构建了在NS启动子控制下表达绿色荧光蛋白（GFP）的转基因报告小鼠（NS-GFP转基因小鼠）。在成年NS-GFP转基因睾丸中，GFP和内源性NS蛋白在精原细胞和精母细胞中的表达相关，但GFP也在伸长的精子细胞和精子中异位表达。然而，在NS-GFP转基因胚胎、新生小鼠和10日龄幼鼠的睾丸中，GFP表达与发育中的生殖细胞中的内源性NS表达密切一致。与之前的一份报告相反，我们的结果支持新生睾丸中存在具有长期重建能力的精原干细胞。此外，我们的数据表明，在青春期前，NS表达与细胞周期状态无关，并且强烈的NS表达对于维持生殖系干细胞增殖能力至关重要。我们得出结论，NS是青春期前精子发生过程中生殖细胞谱系未分化状态的标志物。
