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

Abstract

Sertoli cells (SCs) play a central role in the development of germ cells within functional testes and exhibit varying morphology during spermatogenesis. This present study investigated the seasonal morphological changes in SCs in the reproductive cycle of Pelodiscus sinensis by light microscopy, transmission electron microscopy (TEM), and immunohistochemistry. During hibernation period with the quiescent of spermatogenesis, several autophagosomes were observed inside the SCs, the processes of which retracted. In early spermatogenesis, when the germ cells started to proliferate, the SCs contained numerous lipid droplets instead of autophagosomes. In late spermatogenesis, the SCs processes became very thin and contacted several round/elongated spermatids in pockets. At this time, abundant endoplasmic reticulum and numerous mitochondria were present in the SCs. The organization of the tight junctions and the adherens junctions between the SCs and germ cells also changed during the reproductive cycle. Moreover, SCs were involved in the formation of cytoplasmic bridges, phagophores, and exosome secretions during spermatogenesis. Tubulobulbar complexes (TBC) were also developed by SCs around the nucleus of the spermatid at the time of spermiation. Strong, positive expression of vimentin was noted on the SCs during late spermatogenesis compared with the hibernation stage and the early stage of spermatogenesis. These data provide clear cytological evidence about the seasonal changes in SCs, corresponding with their different roles in germ cells within the Chinese soft‐shelled turtle Pelodiscus sinensis.

Molecular and Cellular Mechanisms of Apoptosis during Dissociated Spermatogenesis

“…Strikingly, positive staining was observed most frequently in spermatids and spermatozoa during the spermatogenically quiescent phase, and typical apoptotic morphology was also demonstrated in TEM samples. Our H&E staining and previous studies demonstrated that the germ cells of male P. sinensis progressed through the process of spermatogenesis as a single cohort, leading to one spermiation event (Zhang et al, 2015; Nisar et al, 2016). Indeed, the residual spermatids and spermatozoa in the seminiferous tubules needed to be eliminated, which was an essential program for the next spermatogenesis cycle in the Chinese soft-shelled turtle (Zhang et al, 2007).…”

“…P. sinensis , like most temperate freshwater turtles, has a typical pattern of episodic germ cell development (Zhang et al, 2007; Ullah et al, 2014). The spermatogenesis of P. sinensis initiates in the spring and continues through summer and fall, with one massive release of mature sperm in early November, while it is inactive throughout the rest of the year (December to next April, the hibernation season; Nisar et al, 2016). Thus, the Chinese soft-shelled turtle can be used as a potential model organism to explore the molecular mechanisms of the dissociated spermatogenesis system.…”

Novel cellular evidence of lipophagy within the Sertoli cells during spermatogenesis in the turtle

“…These elongating steps of spermiogenesis were apically accumulated within the pockets of the Sertoli cell processes and were released in the lumen with spermiation [ 24 ]. Moreover, we observed numerous LDs within the Sertoli cells in May than in October by TEM and ORO staining, and our previous study reported that the Sertoli cells contain abundant LDs during early spermatogenesis as compared to late spermatogenesis [ 30 ]. These LDs can be used for nourishing the germ cells.…”

In vivo autophagy and biogenesis of autophagosomes within male haploid cells during spermiogenesis

“…During spermiogenesis, efficient removal of cytoplasm is thought to be important for the generation of motile and functional spermatozoa, but this mechanism remains poorly understood [ 27 ]. Previously proposed mechanisms suggest that the elimination of residual bodies and cytoplasm are mediated by the Sertoli cells via engulfment [ 28 , 29 ]. However, the role of the germ cells in this process is largely understudied [ 30 ].…”