Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing 210023, China.
Genes (Basel). 2021 Nov 10;12(11):1780. doi: 10.3390/genes12111780.
During embryonic development in mammals, the testicles generally descend into the scrotum, making the testicular temperature 2-4 °C lower than the core temperature via heat exchange and clearance, and thus more beneficial for normal spermatogenesis. Failure to descend, known as cryptorchidism, carries a series of risks such as infertility and testicular cancer. However, some mammals have evolved abdominal testes while maintaining healthy reproduction. To explore the underlying molecular mechanism, we conducted comparative genomic analyses and functional assays on the spermatogenesis-related ubiquitin-proteasome system (UPS) genes essential to sperm formation in representative laurasiatherians. Here, positive selection and rapid evolution of spermatogenesis-related UPS genes were identified in the abdominal testicular laurasiatherians. Moreover, potential convergent amino acids were found between distantly related species with similar abdominal testicles and functional analyses showed RNF8 (V437I) in abdominal testicular species (437I) has a stronger ubiquitination ability, which suggests that the mammals with abdominal testes might exhibit enhanced sperm cell histone clearance to maintain sperm formation. This evidence implies that, in response to "cryptorchidism injury", spermatogenesis-related UPS genes in the abdominal testicular species might have undergone adaptive evolution to stabilize sperm formation. Thus, our study could provide some novel insights into the reproductive adaptation in abdominal testicular mammals.
在哺乳动物的胚胎发育过程中，睾丸通常会下降到阴囊中，通过热交换和清除使睾丸温度比核心温度低 2-4°C，从而更有利于正常的精子发生。如果睾丸没有下降，即隐睾症，会带来一系列风险，如不育和睾丸癌。然而，一些哺乳动物在保持健康繁殖的情况下，已经进化出了腹部睾丸。为了探索潜在的分子机制，我们对与精子形成相关的泛素-蛋白酶体系统（UPS）基因进行了比较基因组分析和功能分析，这些基因对代表性有胎盘哺乳动物的精子发生至关重要。在这里，我们在腹部睾丸有胎盘哺乳动物中鉴定出了与精子发生相关的 UPS 基因的正选择和快速进化。此外，在具有相似腹部睾丸的远缘物种之间发现了潜在的趋同氨基酸，功能分析表明，腹部睾丸物种中的 RNF8（V437I）具有更强的泛素化能力，这表明具有腹部睾丸的哺乳动物可能表现出增强的精子细胞组蛋白清除能力，以维持精子形成。这一证据表明，在“隐睾损伤”的情况下，腹部睾丸物种中的与精子发生相关的 UPS 基因可能经历了适应性进化，以稳定精子形成。因此，我们的研究可以为腹部睾丸哺乳动物的生殖适应提供一些新的见解。
