14-3-3 Protein Regulates Cell Adhesion in the Seminiferous Epithelium of Rat Testes

Abstract

Polarity proteins have been implicated in regulating and maintaining tight junction (TJ) and cell polarity in epithelia. Here we report 14-3-3theta, the homolog of Caenorhabditis elegans Par5 in mammalian cells, which is known to confer cell polarity at TJ, is found at the apical ectoplasmic specialization (ES), a testis-specific adherens junction type restricted to the Sertoli cell-elongating spermatid interface, in which TJ is absent. 14-3-3theta was shown to play a critical role in conferring cell adhesion at the apical ES. A loss of 14-3-3theta expression at the apical ES was detected in the seminiferous epithelium before spermiation. Involvement of 14-3-3theta in Sertoli cell adhesion was confirmed by its knockdown by RNA interference in Sertoli cells cultured in vitro with established TJ permeability barrier that mimicked the blood-testis barrier (BTB) in vivo. Mislocalization of N-cadherin and zonula occludens-1, but not alpha- and beta-catenins, was observed after 14-3-3theta knockdown in Sertoli cells, moving from the cell-cell interface to cytosol, indicating a disruption of cell adhesion. Studies by endocytosis assay illustrated that this loss of cell adhesion was mediated by an increase in the kinetics of endocytosis of N-cadherin and junctional adhesion molecule-A at the BTB, which may represent a general mechanism by which polarity proteins regulate cell adhesion. In summary, the testis is using 14-3-3theta to regulate cell adhesion at the apical ES to facilitate spermiation and at the BTB to facilitate the transit of preleptotene spermatocytes at stages VIII-IX of the epithelial cycle. 14-3-3theta may act as a molecular switch that coordinates these two cellular events in the seminiferous epithelium during spermatogenesis.

Regulation of blood–testis barrier dynamics by TGF-β3 is a Cdc42-dependent protein trafficking event

“…In fact, Cdc42 is known to be involved in targeting of proteins to the basolateral domain of epithelial cells (19,24). Together with the previously published results in which Par6 and 14-3-3 (also known as Par5) were shown to be involved in endocytic vesicle-mediated protein trafficking at the BTB (25), it is likely that Cdc42 is working in concert with Par6 and 14-3-3 to play a dual role in regulating BTB dynamics. First, Cdc42 facilitates TGF-β3-enhanced endocytosis to disrupt "old" TJ-fibrils above the migrating spermatocytes.…”

Restricted Arp3 expression in the testis prevents blood–testis barrier disruption during junction restructuring at spermatogenesis

“…Furthermore, polarity proteins such as Par6 and 14-3-3 (also known as Par5) are highly expressed at the apical ES but at the convex side of the elongating spermatids. These polarity proteins are also integrated components of this anchoring device (25,26) and function to maintain proper spermatid orientation (25). It is likely that the concerted effects of polarity proteins Par6 and 14-3-3 at the convex side and N-WASP-Arp2/3 complex at the concave side of the spermatid head provide the necessary machineries to maintain spermatid orientation.…”

Differential effects of c-Src and c-Yes on the endocytic vesicle-mediated trafficking events at the Sertoli cell blood-testis barrier: an in vitro study

“…testis; spermatogenesis; seminiferous epithelial cycle; blood-testis barrier; endosome; transcytosis; recycling; ectoplasmic specialization; tight junction; c-Yes; c-Src STUDIES HAVE SHOWN that endocytic vesicle-mediated proteintrafficking events that take place in the seminiferous epithelium during the epithelial cycle are crucial to spermatogenesis (7,40,41), similar to their role in regulating cellular events in other tissue barriers, such as membrane traffic (37), autophagy (27), and intracellular cargo trafficking (8). For instance, protein endocytosis, transcytosis, and recycling are necessary for the maintenance of the blood-testis barrier (BTB) integrity during the transport of preleptotene spermatocytes at the BTB that takes places at stage VIII of the epithelial cycle (36,45,46,52). In brief, proteins at the "old" BTB site located above the preleptotene spermatocytes that are connected in clones via intercellular bridges are endocytosed, transcytosed, and recycled to assemble the "new" BTB located beneath these cells (52).…”