In males, germ cells undergo meiosis and post-meiotic differentiation within a protective environment inside the seminiferous tubules. This environment is created by the blood-testis barrier (BTB), of which tight junctions (TJ) between Sertoli cells are a major structural component. The BTB forms at puberty and remains essential for male fertility as loss of BTB function causes infertility. Our current understanding is that TJ formation is driven by hormones (FSH, testosterone) and local factors but a role for germ cells is not clear. However, we demonstrated that BTB function in vivo was significantly improved when round spermatids (rSTs) were present (1). Hence the aim of this study was to define the impact of rSTs on Sertoli cell TJs in vitro. 20-day old rat Sertoli cells were cultured to form a functional monolayer onto which isolated adult rST were added. TJ function was measured by transepithelial electrical resistance (TER) and a tracer diffusion assay measured changes in molecular weight permeability.
Sertoli cells alone formed stable TJs within 3 days, and FSH and testosterone stimulated TER >2-fold compared to control. Stimulated cells also showed a decreased (~2-fold) permeability to small- (3-5kD, 10kD) and medium- (70kD) sized tracers, but no change for a large (500kD) tracer. Importantly, the addition of rSTs significantly enhanced TJ and barrier function of the Sertoli cell monolayer; TER increased further and the cells acquired the ability to restrict the passage of higher molecular weight molecules (70 & 500kD), thus forming a more functionally mature barrier. This stimulatory effect of rSTs was time-, contact-, and cell number- dependent, and was not observed in an unrelated HEK cell control. We conclude that rSTs contribute to the establishment of a functional barrier in Sertoli cells that creates a specialised milieu necessary for sperm production.
* equal contributions