Sperm storage and spermatozoa interaction with epithelial cells in oviduct of Chinese soft‐shelled turtle, Pelodiscus sinensis

Abstract

Spermatozoa are known to be stored within the female genital tract after mating in various species to optimize timing of reproductive events such as copulation, fertilization, and ovulation. The mechanism supporting long-term sperm storage is still unclear in turtles. The aim of this study was to investigate the interaction between the spermatozoa and oviduct in Chinese soft-shelled turtle by light and electron microscopy to reveal the potential cytological mechanism of long-term sperm storage. Spermatozoa were stored in isthmus, uterine, and vagina of the oviduct throughout the year, indicating long-term sperm storage in vivo. Sperm heads were always embedded among the cilia and even intercalated into the apical hollowness of the ciliated cells in the oviduct mucosal epithelium. The stored spermatozoa could also gather in the gland conduit. There was no lysosome distribution around the hollowness of the ciliated cell, suggesting that the ciliated cells of the oviduct can support the spermatozoa instead of phagocytosing them in the oviduct. Immune cells were sparse in the epithelium and lamina propria of oviduct, although few were found inside the blood vessel of mucosa, which may be an indication of immune tolerance during sperm storage in the oviduct of the soft-shelled turtle. These characteristics developed in the turtle benefited spermatozoa survival for a long time as extraneous cells in the oviduct of this species. These findings would help to improve the understanding of reproductive regularity and develop strategies of species conservation in the turtle. The Chinese soft-shelled turtle may be a potential model for uncovering the mechanism behind the sperm storage phenomenon.

Cytological study on Sertoli cells and their interactions with germ cells during annual reproductive cycle in turtle

“…, ; Chen et al. ). To the best of our knowledge, the seasonal changes in SC structure within the Chinese soft‐shelled turtle have not been reported.…”

“…Interestingly, in the Chinese soft-shelled turtle (Pelodiscus sinensis), spermatogenesis is active through late spring, summer, and fall (May to October), ending in a temporal rather than a spatial pattern, resulting in one massive release of sperm in late October or early November. It remains quiescent (hibernation period) throughout the rest of the year (December to April), so it is a potential model organism with which to determine seasonal effects in China (Zhang et al 2008Chen et al 2015). To the best of our knowledge, the seasonal changes in SC structure within the Chinese soft-shelled turtle have not been reported.…”

Expression of TLR2/4 on Epididymal Spermatozoa of the Chinese Soft‐Shelled Turtle Pelodiscus sinensis During the Hibernation Season

“…Unlike mammals and birds, turtle spermatozoa are known to be stored in the epididymis and oviduct for a long period of time (6–7 months in epididymis and more than 1 year in oviduct) (Xiangkun et al, ; Chen et al, ), as copulation, fertilization, and ovulation are not synchronized in turtles. Many factors affect sperm storage in vivo .…”

Cellular Evidence of Exosomes in the Reproductive Tract of Chinese Soft‐Shelled Turtle Pelodiscus sinensis

“…Nonciliated or secretory cells are involved in the production of the lubricating fluid, which maintains a moist and clean oviduct lumen (Sarkar et al., ; Gadella, ; Mondéjar et al., ). Epithelium secretions have also been reported in some reptiles (Srinivas et al., ; Sever and Hamlett, ; Chen et al., ), amphibians (Akbarsha et al., ), and mammals (Killian, ). The secretory nature of epithelium, production, and functions of these secretions is the matter of controversial dialogue (Sasanami et al., ).…”