Abstract: Seasonal reproduction is a life history adaptation that helps animals survive under the changes of their environments. Seasonal reproduction is tightly regulated by the hypothalamus-pituitary-gonad (HPG) axis. Plateau zokor (Eospalax baileyi) is an underground rodent native to the Qinghai-Tibet plateau and they breed only in April to July. How gametogenesis and reproductive activities are regulated in underground mammals remains largely unclear. In the present study, we showed that spermatogenesis in adult male plateau zokor was seasonally regulated. Seminiferous tubules of plateau zokor contained well-developed germ cells including elongated sperm during breeding season (April to June). Based on the cell association and morphological features, the seminiferous epithelium can be divided into 10 stages. During non-breeding season, seminiferous tubules only contained spermatogonia and Sertoli cells, indicating spermatogenesis had been arrested. Levels of gonadotropin-releasing hormone, luteinizing hormone and testosterone were significantly increased in breeding season with notable reduction of melatonin (P < 0.05), while follicle-stimulating hormone level did not show a significant change. Further analysis revealed that biogenesis of retinoic acid, responsible for spermatogonial differentiation, was changed dramatically. As expected, supplementation of retinoic acid induced resumption of spermatogenesis in reproductively dormant animals. Together, these data demonstrated morphological features and key regulatory factors of seasonal spermatogenesis in plateau zokor. This study can provide a reference for understanding similar mechanism existed in other underground rodents.

Key words: Plateau zokor, Seasonal reproduction, Spermatogenesis, Testosterone, Retinoic acid, Spermatogonia

摘要： 季节性繁殖是动物在长期进化中为适应环境变化而形成的生活史特征，受光周期和下丘脑-垂体-性腺轴的严密调控。高原鼢鼠（Eospalax baileyi）是青藏高原特有的地下啮齿类动物，其繁殖活动表现出明显的季节性。然而，地下啮齿类动物精子发生的形态特征和关键调控因子尚不明确。本研究以成年高原鼢鼠为研究对象，发现繁殖期成年雄性睾丸曲精小管内有各级生殖细胞，附睾内有长形精子，生精上皮可分为10个期；而非繁殖期睾丸重量显著下降，曲精小管内仅见精原细胞和支持细胞。激素水平检测结果显示，与非繁殖期相比，繁殖期褪黑素水平显著降低（P < 0.05），促性腺激素释放激素、促黄体生成素和睾酮水平显著升高（P < 0.05），而卵泡刺激素水平无显著差异。进一步研究发现，精原细胞分化的关键诱导因子维甲酸水平和其调控基因表达均呈季节性变化，且外源维甲酸注射能够诱导非繁殖期高原鼢鼠重启精子发生。综上，高原鼢鼠虽为地下动物，但其精子发生与下丘脑-垂体-性腺轴激素水平明显相关，且受睾酮和维甲酸信号的调控。本研究首次揭示了高原鼢鼠精子发生的形态学特征和关键调控因子，为理解季节性繁殖动物尤其是地下啮齿类动物生殖生理的调控机制提供了重要参考。

关键词: 高原鼢鼠, 季节性繁殖, 精子发生, 睾酮, 维甲酸, 精原细胞