Telomerase inactivation causes loss of the male germline in worms, fish, and mice, indicating a conserved dependence on telomere maintenance in this cell lineage. Here, using telomerase reverse transcriptase (Tert) reporter mice, we found that very high telomerase expression is a hallmark of undifferentiated spermatogonia, the mitotic population where germline stem cells reside. We exploited these high telomerase levels as a basis for purifying undifferentiated spermatogonia using fluorescence-activated cell sorting. Telomerase levels in undifferentiated spermatogonia and embryonic stem cells are comparable and much greater than in somatic progenitor compartments. Within the germline, we uncovered an unanticipated gradient of telomerase activity that also enables isolation of more mature populations. Transcriptomic comparisons of Tert(High) undifferentiated spermatogonia and Tert(Low) differentiated spermatogonia by RNA sequencing reveals marked differences in cell cycle and key molecular features of each compartment. Transplantation studies show that germline stem cell activity is confined to the Tert(High) cKit(-) population. Telomere shortening in telomerase knockout strains causes depletion of undifferentiated spermatogonia and eventual loss of all germ cells after undifferentiated spermatogonia drop below a critical threshold. These data reveal that high telomerase expression is a fundamental characteristic of germline stem cells, thus explaining the broad dependence on telomerase for germline immortality in metazoans.

中文翻译：

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高端粒酶是未分化精原细胞的标志，是维持雄性生殖系干细胞所必需的。

端粒酶失活会导致蠕虫、鱼类和小鼠中雄性种系的丢失，表明该细胞谱系对端粒维持的保守依赖。在这里，使用端粒酶逆转录酶 (Tert) 报告小鼠，我们发现非常高的端粒酶表达是未分化精原细胞的标志，这是生殖系干细胞所在的有丝分裂群体。我们利用这些高端粒酶水平作为使用荧光激活细胞分选纯化未分化精原细胞的基础。未分化的精原细胞和胚胎干细胞中的端粒酶水平与体细胞祖细胞区室中的端粒酶水平相当并且高得多。在种系中，我们发现了一个意想不到的端粒酶活性梯度，它也能够分离出更成熟的种群。通过 RNA 测序对叔（高）未分化精原细胞和叔（低）分化精原细胞进行转录组学比较，揭示了细胞周期和每个隔室的关键分子特征的显着差异。移植研究表明，种系干细胞活性仅限于 Tert(High) cKit(-) 群体。端粒酶敲除菌株中的端粒缩短会导致未分化精原细胞耗尽，并在未分化精原细胞下降到临界阈值以下后最终丢失所有生殖细胞。这些数据表明端粒酶的高表达是种系干细胞的一个基本特征，从而解释了后生动物种系永生对端粒酶的广泛依赖。