Development of Sertoli cell junctional specializations and the distribution of the tight‐junction‐associated protein ZO‐1 in the mouse testis

Abstract

Basally located tight junctions between Sertoli cells in the postpubertal testis are the largest and most complex junctional complexes known. They form at puberty and are thought to be the major structural component of the "blood-testis" barrier. We have now examined the development of these structures in the immature mouse testis in conjunction with immunolocalization of the tight-junction-associated protein ZO-1 (zonula occludens 1). In testes from 5-day-old mice, tight junctional complexes are absent and ZO-1 is distributed generally over the apicolateral, but not basal, Sertoli cell membrane. As cytoskeletal and reticular elements characteristic of the mature junction are recruited to the developing junctions, between 7 and 14 days, ZO-1 becomes progressively restricted to tight junctional regions. Immunogold labeling of ZO-1 on Sertoli cell plasma membrane preparations revealed specific localization to the cytoplasmic surface of tight junctional regions. In the mature animal, ZO-1 is similarly associated with tight junctional complexes in the basal aspects of the epithelium. In addition, it is also localized to Sertoli cell ectoplasmic specializations adjacent to early elongating, but not late, spermatids just prior to sperm release. Although these structures are not tight junctions, they do have a similar cytoskeletal arrangement, suggesting that ZO-1 interacts with the submembrane cytoskeleton. These results show that, in the immature mouse testis, ZO-1 is present on the Sertoli cell plasma membrane in the absence of recognizable tight junctions. In the presence of tight junctions, however, ZO-1 is found only at the sites of junctional specializations associated with tight junctions and with elongating spermatids.

Regulation of blood-testis barrier dynamics: an in vivo study

“…3A). Weak staining was also found around early elongating spermatids, consistent with an earlier report (Byers et al, 1991). This immunostaining pattern of ZO-1 in the seminiferous epithelium persisted until 7 hours after the CdCl2 treatment (Fig.…”

“…Immunohistochemical localization of ZO-1 in the seminiferous epithelium after CdCl2 treatment The localization of ZO-1, a TJ peripheral adaptor found at the site of the BTB (Byers et al, 1991), in the seminiferous epithelium was examined to assess its changes during the CdCl2-induced BTB damage. Immunoreactive ZO-1 appeared as reddish-brown precipitates at the basal compartment of normal rat seminiferous tubules consistent with its localization at the site of the BTB (Fig.…”

AKAP9 Is Essential for Spermatogenesis and Sertoli Cell Maturation in Mice

“…We hypothesized that abnormal Sertoli cell numbers and fertility defects in males reflected a failure to establish junctions characteristic of the BTB, a prediction substantiated by the abnormal localization of germ cells (Figure 4). In prepubertal animals, testis ZO-1 is localized apicolaterally (Stevenson et al 1986;Anderson et al 1988;Byers et al 1991), and shifts to associate almost exclusively with Sertoli cell basolateral tight junctions in peri-and postpubertal mice (Byers et al 1991). In the wild-type adult testis, we observed ZO-1 proximal to the basement membrane ( Figure 7A, red signal, white arrows; higher magnification in Figure 7C), whereas Akap9 mei2.5/mei2.5 testes exhibit ZO-1 expression towards the apical surface of Sertoli cells, with weak or no localization along the seminiferous tubule basement membrane ( Figure 7B, open arrowheads; higher magnification in Figure 7D).…”

“…Basal tight junctions between Sertoli cells form the principal structural component of the BTB by day 16 (Nagano and Suzuki 1976). The expression of the tightjunction protein, zonula occludens 1 (ZO-1, also known as TJP1), in the testis is restricted primarily to the inter-Sertoli cell tight junction interface by puberty (Byers et al 1991). In Sertoli cells, ZO-1 is known to interact with Cx43 to regulate gap junction integrity (Giepmans and Moolenaar 1998;Toyofuku et al 1998;Hunter et al 2005) and proliferation (Rhett et al 2011) and thus is an important functional marker for Sertoli cell tight junctions and maturation.…”

AKAP9, a Regulator of Microtubule Dynamics, Contributes to Blood-Testis Barrier Function

“…15 To delineate the role of AKAP9 and its MT-regulating activity in BTB function, we generated mice with conditional and inducible Akap9 deletion for spatiotemporal restriction of Akap9 deficiency and mice with global Akap9 deletion. The BTB, established at postnatal day 15 in mice, 16 separates the mitotic/spermatogonial and meiotic/ spermatocyte compartment and undergoes remodeling at stage VIII of the seminiferous epithelial cell cycle to facilitate the transport of preleptotene spermatocytes across the barrier so that meiosis I/II and subsequent postmeiotic spermatid development can take place in the adluminal compartment behind the BTB. 1 We exploited the VEcadherin promoter for a conditional Cre recombinase deletion of Akap9 in the testes because in addition to its well known expression in endothelial cells, 17 VE-cadherin exhibits epithelial cycle stageespecific expression in the Sertoli cells 18,19 and in differentiating spermatids at stage II and elongated spermatids of mouse testes.…”