An autocrine axis in the testis that coordinates spermiation and blood–testis barrier restructuring during spermatogenesis

Abstract

The mechanism(s) that regulate and coordinate the events of spermiation and blood-testis barrier (BTB) restructuring in the seminiferous epithelium that occur concurrently at stage VIII of the seminiferous epithelial cycle of spermatogenesis are unknown. In this report, fragments derived from the laminin complex composed of laminin ␣3, ␤3, and ␥3 chains (laminin-333) at the apical ectoplasmic specialization (apical ES) were shown to modulate BTB dynamics directly and/or indirectly via hemidesmosome. Experiments were performed using cultured Sertoli cells with functional tight junction (TJ) barrier and the ultrastructural features of the BTB but not apical ES. Recombinant protein fragments of laminin ␤3 and ␥3 chains were shown to reduce the protein levels of occludin and ␤1-integrin dose dependently at the Sertoli-Sertoli and Sertoli-basement membrane interface, respectively, thereby destabilizing the BTB permeability function. These results were corroborated by transient overexpression of laminin fragments in Sertoli cells. To further assess the role of ␤1-integrin in hemidesmosome, knockdown of ␤1-integrin in Sertoli cells by RNAi was found to associate with occludin redistribution at the SertoliSertoli cell interface, wherein occludin moved away from the cell surface and became associated with endosomes, thereby destabilizing the BTB. In short, an apical ES-BTB-hemidesmosome autocrine regulatory axis was identified in testes, coordinating the events of spermiation and BTB restructuring that occur at the opposite ends of the seminiferous epithelium during spermatogenesis.ectoplasmic specialization ͉ hemidesmosome ͉ seminiferous epithelium ͉ Sertoli cells ͉ tight junction D uring spermatogenesis, preleptotene/leptotene spermatocytes at the basal compartment traverse the blood-testis barrier (BTB) at stages ϷVIII-IX of the seminiferous epithelial cycle in adult rat testes, entering the adluminal compartment for further development (1). This event takes place concurrently with spermiation, wherein fully developed spermatids (i.e., spermatozoa) detach from the epithelium at the luminal edge, entering the tubule lumen for their eventual maturation in the epididymis. These morphologic changes, which occur at the opposite ends of the Sertoli cell epithelium, were first described in the 1950s (2). In this report, we provide compelling evidence regarding the mechanism that regulates and coordinates these events. The idea was based on a recent study in which a blockade of the laminin function at the apical ectoplasmic specialization (apical ES) by specific antibodies led to spermatid exfoliation and BTB restructuring (3), even though it was unclear how the anti-laminin ␥3 IgG traversed the BTB to reach the apical ES. Nonetheless, this study shows that a disruption of the apical ES may lead to a transient BTB disruption, illustrating a plausible physiological link between these two ultrastructures.The apical ES is a testis-specific adherens junction (AJ) type that anchors developing spermatids to the Sertoli cell in the ...

Focal adhesion kinase-Tyr 407 and -Tyr 397 exhibit antagonistic effects on blood–testis barrier dynamics in the rat

“…The function of p-FAK-Tyr 397 at this site is not well understood, but it may be associated with the release of mature spermatids from the epithelium at spermiation (1,5). Based on results in this study, we provide unique details in the apical ES-BTB functional axis in the seminiferous epithelium (27) regarding how spermatid release and BTB restructuring, which occur simultaneously at the opposite ends of the epithelium, are coordinated during stage VIII of the rat seminiferous epithelial cycle (1). On the release of spermatids, the dissolution of the protein complex consisting of integrin/laminin/p-FAK-Tyr 397 may lead to a transient surge of free p-FAK-Tyr 397 in the Sertoli cell cytoplasm, which induces restructuring of BTB junction complexes to allow the entry of preleptotene spermatocytes into the adluminal compartment.…”

The β1-integrin-p-FAK-p130Cas-DOCK180-RhoA-vinculin is a novel regulatory protein complex at the apical ectoplasmic specialization in adult rat testes

“…These findings are consistent with a recent report using dual-labeled immunofluorescence analysis to assess the localization of β1-integrin in the adult rat testis. 81 Immunoreactive β1-integrin was found at the apical ES as early as in stage X (Fig. 3c) Fig.…”

Molecular mechanisms by which hormones and cytokines regulate cell junction dynamics in the testis

“…The recently identified autocrine axis, coordinating the events of BTB restructuring and spermiation which take place concurrently at the opposite ends of the seminiferous epithelium, is proposed to be mediated by fragments of laminin chains released from the dissociation of spermatid-Sertoli cell adhesion (Yan et al 2008b). …”