Biology and regulation of ectoplasmic specialization, an atypical adherens junction type, in the testis

Abstract

Anchoring junctions are cell adhesion apparatus present in all epithelia and endothelia. They are found at the cell-cell interface (adherens junction (AJ) and desmosome) and cell-matrix interface (focal contact and hemidesmosome). In this review, we focus our discussion on AJ in particular the dynamic changes and regulation of this junction type in normal epithelia using testis as a model. There are extensive restructuring of AJ (e.g., ectoplasmic specialization, ES, a testis-specific AJ) at the Sertoli-Sertoli cell interface (basal ES) and Sertoli-elongating spermatid interface (apical ES) during the seminiferous epithelial cycle of spermatogenesis to facilitate the migration of developing germ cells across the seminiferous epithelium. Furthermore, recent findings have shown that ES also confers cell orientation and polarity in the seminiferous epithelium, illustrating that some of the functions initially ascribed to tight junctions (TJ), such as conferring cell polarity, are also part of the inherent properties of the AJ (e.g., apical ES) in the testis. The biology and regulation based on recent studies in the testis are of interest to cell biologists in the field, in particular their regulation, which perhaps is applicable to tumorigenesis.

Autophagy is required for ectoplasmic specialization assembly in sertoli cells

“…6,8 The ES is an actin microfilament-rich anchoring device using F-actin for attachment 9 at the SertoliSertoli cell interface known as the basal ES (bES), which together with the tight junctions, gap junctions and the desmosome-like junction create the blood-testis barrier (BTB). [9][10][11][12] The apical compartment of the Sertoli cell-elongating spermatid interface, called apical ES (aES), interacts with the acrosome region of the elongating spermatid and mechanically grasps the head of spermatids to undergo rapid elongation and maturation. 6,7,9,11,13 The main roles of the apical ES include shaping the spermatid head, facilitating spermatid cell movement, orienting the elongated spermatid and releasing mature spermatozoa during spermiation.…”

“…[9][10][11][12] The apical compartment of the Sertoli cell-elongating spermatid interface, called apical ES (aES), interacts with the acrosome region of the elongating spermatid and mechanically grasps the head of spermatids to undergo rapid elongation and maturation. 6,7,9,11,13 The main roles of the apical ES include shaping the spermatid head, facilitating spermatid cell movement, orienting the elongated spermatid and releasing mature spermatozoa during spermiation. 10,13 In the Sertoli cell-elongating spermatid interface, the apical ES consists of a narrow layer of hexagonally packed, parallel actin bundles sandwiched between the Sertoli cell plasma membrane and an endoplasmic reticulum (ER) cistern on the Sertoli cell side of the plasma membrane.…”

“…9,19 The extensive restructuring of basal and apical ES is crucial to spermatogenesis, and recent studies have shown many molecules and signaling pathways participate in ES restructuring. 6,9,11,14,16 However, the precise mechanism remains elusive.…”

Breast cancer resistance protein (Bcrp) and the testis—an unexpected turn of events

“…The BTB also segregates the seminiferous epithelium into the basal and the adluminal compartments (Figure 2). Unlike other blood-tissue barriers, [24][25][26] which are composed almost exclusively of capillary endothelial TJs, microvessels in the interstitium between seminiferous epithelium in the testes contribute virtually no barrier function to the BTB. [27][28][29][30] However, in rodents, the peritubular myoid cell layer in the tunica propria that lies behind the basement membrane and the type I collagen layer was found to restrict the diffusion of lanthanum salt and colloidal carbon or thorium in ,75% of the tubules examined, 30,31 making it a contributing component to the BTB.…”

“…14,25 Bcrp displays a restrictive spatiotemporal pattern of expression during the epithelial cycle, such that it is only detected at the apical ES in stage VI-VIII tubules, but not at stage IX-XIV or I-V (Figure 3). 33 In short, unlike other drug transporters, such as P-glycoprotein and Oatp3, 34,35 Bcrp is not a component of the Sertoli cell BTB, 33 but is stage specifically expressed by Sertoli cells and spermatid in addition to abundant expression by endothelial cells and peritubular myoid cells in rat testes.…”