Center for Reproductive Genomics, Cornell University, Ithaca, NY, United States of America.
Department of Biomedical Sciences, Cornell University, Ithaca, NY, United States of America.
PLoS Genet. 2019 Mar 20;15(3):e1007810. doi: 10.1371/journal.pgen.1007810. eCollection 2019 Mar.
Spermatogenesis is the process by which male gametes are formed from a self-renewing population of spermatogonial stem cells (SSCs) residing in the testis. SSCs represent less than 1% of the total testicular cell population in adults, but must achieve a stable balance between self-renewal and differentiation. Once differentiation has occurred, the newly formed and highly proliferative spermatogonia must then enter the meiotic program in which DNA content is doubled, then halved twice to create haploid gametes. While much is known about the critical cellular processes that take place during the specialized cell division that is meiosis, much less is known about how the spermatocytes in the "first-wave" in juveniles compare to those that contribute to long-term, "steady-state" spermatogenesis in adults. Given the strictly-defined developmental process of spermatogenesis, this study explored the transcriptional profiles of developmental cell stages during testis maturation. Using a combination of comprehensive germ cell sampling with high-resolution, single-cell-mRNA-sequencing, we have generated a reference dataset of germ cell gene expression. We show that discrete developmental stages of spermatogenesis possess significant differences in the transcriptional profiles from neonates compared to juveniles and adults. Importantly, these gene expression dynamics are also reflected at the protein level in their respective cell types. We also show differential utilization of many biological pathways with age in both spermatogonia and spermatocytes, demonstrating significantly different underlying gene regulatory programs in these cell types over the course of testis development and spermatogenic waves. This dataset represents the first unbiased sampling of spermatogonia and spermatocytes during testis maturation, at high-resolution, single-cell depth. Not only does this analysis reveal previously unknown transcriptional dynamics of a highly transitional cell population, it has also begun to reveal critical differences in biological pathway utilization in developing spermatogonia and spermatocytes, including response to DNA damage and double-strand breaks.
精子发生是指雄性配子从睾丸中自我更新的精原干细胞（SSC）群体中形成的过程。SSC 占成人睾丸细胞总数的不到 1%，但必须在自我更新和分化之间达到稳定的平衡。一旦发生分化，新形成的高度增殖精原细胞必须进入减数分裂程序，在此程序中 DNA 含量加倍，然后减半两次以产生单倍体配子。虽然人们对减数分裂这一特殊细胞分裂过程中发生的关键细胞过程有了很多了解，但对于青少年“第一波”中的精母细胞与成年后长期“稳定状态”的精子发生相比有何不同，人们知之甚少。鉴于精子发生的严格发育过程，本研究探讨了睾丸成熟过程中发育细胞阶段的转录谱。通过综合全面的精细胞采样与高分辨率、单细胞 RNA 测序相结合，我们生成了一个精细胞基因表达的参考数据集。我们发现，与新生儿相比，精子发生的离散发育阶段在转录谱上与青少年和成人有显著差异。重要的是，这些基因表达动态在各自的细胞类型中也反映在蛋白质水平上。我们还展示了随着年龄的增长，在精原细胞和精母细胞中许多生物途径的差异利用，表明在睾丸发育和精子发生波的过程中，这些细胞类型的基础基因调控程序有显著差异。该数据集代表了在高分辨率、单细胞深度下，首次对睾丸成熟过程中的精原细胞和精母细胞进行无偏采样。该分析不仅揭示了高度过渡细胞群以前未知的转录动态，还开始揭示发育中的精原细胞和精母细胞在生物途径利用方面的关键差异，包括对 DNA 损伤和双链断裂的反应。
