Abstract:

To adapt to cyclical changes in their environment, mammals have developed different reproductive strategies over long periods of evolution. Seasonal changes in spermatogenesis are one of the typical adaptive features of seasonally breeding animals. During the reproductive period, spermatogenic cells at all levels of the testicular spermatogenic epithelium differentiate in an orderly manner to produce a steady stream of spermatozoa, whereas during the nonreproductive period, spermatogenic cell development is blocked and the testis degenerates. Seasonal spermatogenesis is cyclic in response to dynamic changes in hormone levels, a process that is tightly regulated by the photoperiod and the Hypothalamic-Pituitary-Gonadal (HPG) axis. As a major environmental signal regulating seasonal reproduction, photoperiod affects gonadotropin-releasing hormone (GnRH) neuronal activity through melatonin-mediated neurotransmission, which in turn acts on the gonads to regulate testosterone secretion and spermatogonial differentiation. In addition, thyroid hormones play a key role in the animal’s response to light signaling and maintenance of the HPG axis. Within the gonads, spermatogenic cell development in non-reproducing animals exhibits different patterns of blockage, including reduced proliferative activity of spermatogonia, autophagy and spermatocyte apoptosis, and detachment, with testosterone-regulated changes in retinoic acid concentration playing a central role in the blockage of spermatogonial differentiation. This article summarizes the mechanisms by which key environmental factors, the reproductive axis, and the testicular microenvironment synergistically regulate seasonal spermatogenesis in mammals, outlining new findings on the regulation of seasonal reproduction in animals. This paper focuses on a more systematic review of the roles of testosterone- and retinoic acid-regulated testicular microenvironments in seasonal spermatogenesis, with a view to providing reference information for the study of the molecular regulatory mechanisms of both on mammalian seasonal spermatogenesis, as well as an in-depth understanding of the physiology of reproduction and physiological ecology of veterinary species, and the development of techniques for the regulation of animal populations.

Key words: Mammal, Seasonal spermatogenesis, Hypothalamic-Pituitary-Gonadal axis, Photoperiod

摘要：

为适应环境的周期性变化，哺乳动物在长期进化中形成了不同的生殖策略。精子发生的季节性变化是季节性繁殖动物典型的适应性特征之一。在繁殖期，睾丸生精上皮的各级生精细胞有序分化以源源不断地生成精子；而在非繁殖期，生精细胞发育阻断，睾丸退化。季节性精子发生随着激素水平的动态变化而呈现周期性变化，该过程主要受光周期和下丘脑-垂体-性腺 (Hypothalamic‑Pituitary‑Gonadal, HPG) 轴的严密调控。作为调控季节性繁殖的主要环境信号，光周期通过褪黑激素介导相关神经递质影响促性腺激素释放激素神经元活动，继而作用于性腺，调控睾酮分泌和生精细胞分化。此外，甲状腺激素也在动物对光信号的响应和HPG轴的维持中发挥关键作用。在性腺内，非繁殖期动物生精细胞发育呈现不同的阻断模式，包括精原细胞增殖活性降低、自噬和精母细胞凋亡以及脱落等，其中睾酮调控的维甲酸浓度变化在生精细胞分化阻断中发挥核心作用。本文总结了关键环境因子、生殖轴和睾丸微环境协同调控哺乳动物季节性精子发生的机制，概括了动物季节性繁殖调控的新发现。文章重点对睾酮-维甲酸信号在季节性精子发生中的调控作用进行了较为系统的综述，以期为两者对哺乳动物季节性精子发生的分子调控机制研究提供参考资料，同时对深入理解兽类繁殖生理和生理生态，开发动物种群调控技术具有重要意义。

关键词: 哺乳动物, 季节性精子发生, 下丘脑-垂体-性腺轴, 光周期