Post-testicular maturation of spermatozoa is crucial for attaining the morphological and functional capabilities needed for successful fertilization. Epididymal epithelia offer a favorable environment for spermatozoa that are stored long term in the turtle epididymis; however, sperm–epithelial interactions during storage, which are enormously important for sperm functional and morphological maturation, are still largely unknown in turtles. The present study examined the epididymis during the sperm-storage period (November–April) in the Chinese soft-shelled turtle (Pelodiscus sinensis). Light and transmission electron microscopy were used to determine the cellular features of each epididymal segment (caput, corpus, and cauda) and their epithelial interactions with the spermatozoa. Spermatozoa were mainly located in the lumena of caput, corpus, and cauda epididymides. Numerous spermatozoa were bound to apical surfaces of the epithelia, and several were even embedded in the epithelial cytoplasm of the caput and corpus epididymides. No embedded spermatozoa were found in the cauda epididymis. In all epididymal segments, principal and clear cells showed the synthetic activity, evidenced by a well-developed endoplasmic reticulum network and high and low electron-dense secretory materials, respectively. Principal and clear cells in the caput and corpus segments showed embedded spermatozoa in electron-dense secretions and in the lipid droplets within the cytoplasm. No lysosomes were observed around the embedded spermatozoa. The lumena of the caput and corpus segments showed few apocrine and low electron density secretions. In the lumen of the cauda epididymidis, different secretions, such as holocrine with low and high electron density and their fragmentation, apocrine, and dictyosome, were found and are summarized. Altogether, sperm physical interactions with secretions either in the cytoplasm of epithelium or in the lumen may support the viability, morphological maintenance, and transfer of various proteins involved in long-term sperm storage in the turtle. This interaction could help us to understand the mechanisms of long-term sperm storage and provide more insights into the reproductive strategies of turtle sperm preservation.

中文翻译：

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附睾上皮及其分泌物与精子的相互作用支持中华鳖 (Pelodiscus sinensis) 长期储存期间的功能和形态变化

精子的睾丸后成熟对于获得成功受精所需的形态和功能能力至关重要。附睾上皮为精子在龟附睾中长期储存提供了有利的环境；然而，储存过程中精子-上皮的相互作用对精子的功能和形态成熟非常重要，但在海龟中仍然很大程度上是未知的。本研究检查了中华鳖精子储存期（11 月至 4 月）的附睾。中华鳖）。光学和透射电子显微镜用于确定每个附睾节段（头、体和尾）的细胞特征及其上皮与精子的相互作用。精子主要分布在头腔、体腔和附睾尾部。许多精子与上皮的顶端表面结合，有几个甚至嵌入到附睾头和附睾体的上皮细胞质中。附睾尾部未发现包埋精子。在所有附睾节段中，主细胞和透明细胞都表现出合成活性，分别由发达的内质网网络和高和低电子密集的分泌材料证明。头节和体节中的主要细胞和透明细胞在电子致密的分泌物中和细胞质内的脂滴中显示出嵌入的精子。在嵌入的精子周围没有观察到溶酶体。头段和体段的管腔显示出很少的大汗腺和低电子密度分泌物。在附睾尾管腔中发现并总结了不同的分泌物，如低电子密度和高电子密度的全分泌及其碎片、顶泌体和网状体。总之，精子与上皮细胞质或腔内分泌物的物理相互作用可能支持龟体内长期精子储存所涉及的各种蛋白质的活力、形态维持和转移。