Relationship of Sertoli-Sertoli Tight Junctions to Ectoplasmic Specialization in Conventional and En Face Views

Abstract

Ectoplasmic specializations are actin filament-endoplasmic reticulum complexes that occur in Sertoli cells at sites of intercellular attachment. At sites between inter-Sertoli cell attachments, near the base of the cells, the sites are also related to tight junctions. We studied the characteristics of ectoplasmic specializations from six species using conventional views in which thin sections were perpendicular to the plane of the membranes, we used rare views in which the sections were in the plane of the membrane (en face views), and we also used the freeze-fracture technique. Tissues postfixed by osmium ferrocyanide showed junctional strands (fusion points between membranes) and actin bundles, actin sheets, or both, which could be visualized simultaneously. En face views demonstrated that the majority of tight junctional strands ran parallel to actin filament bundles. Usually, two tight junctional strands were associated with each actin filament bundle. Parallel tight junctions were occasionally extremely close together (ϳ12 nm apart). Tight junctional strands were sometimes present without an apparent association with organized actin bundles or they were tangential to actin bundles. En face views showed that gap junctions were commonly observed intercalated with tight junction strands. The results taken together suggest a relationship of organized actin with tight junction complexes. However, the occasional examples of tight junction complexes being not perfectly aligned with actin filament bundles suggest that a precise and rigidly organized actin-tight junction relationship described above is not absolutely mandatory for the presence or maintenance of tight junctions. Species variations in tight junction organization are also presented. male reproductive tract, Sertoli cells, sperm motility and transport, spermatogenesis, testis

F-actin-based extensions of the head cyst cell adhere to the maturing spermatids to maintain them in a tight bundle and prevent their premature release in Drosophila testis

“…The mammalian spermatids attach to the Sertoli cell membrane through the apical ES [66]. The F-actin-based ES forms around developing spermatids inside the Sertoli cell [13].…”

Claudin and occludin expression and function in the seminiferous epithelium

“…Although the bands of tight junctions, adherens junctions, and desmosomes support each other functionally through interactions with scaffolding proteins and the cytoskeleton, these different types of cell -cell contact are physically separate from each other in most polarized epithelia (Wong et al 2008). However, at the BTB in Sertoli cells, the tight junctions and specialized adherens junctions (basal ectoplasmic specialization and basal tubulobulbar complex), as well as the basal gap junctions and desmosome-like junctions are all intermingled with each other (Russell & Peterson 1985;Parreira et al 2002;Wong et al 2008). In addition to the tight junctions, the basal ectoplasmic specialization (Yan & Cheng 2005;Lie et al 2006;Yan et al 2007) and desmosome-like junctions (Li et al 2009) appear to be integral, functional components of the BTB.…”

Deficiency of Mkrn2 causes abnormal spermiogenesis and spermiation, and impairs male fertility

“…The ectoplasmic specialization (ES) is a specialized adhesion junction found in Sertoli cells at sites of attachment to elongated spermatids or neighboring Sertoli cells in the testes20. Spermiation failure can be indicative of disruption of ES21.…”

“…As expectedly, the sizes and weights of the testes in Mkrn2 knockout mice were lower than those in normal mouse testes. TEM analysis revealed that impaired ES structure in Mkrn2 knockout mice203031. ES is mainly characterized by the presence of a unique junction plaque containing parallel actin bundles sandwiched between the plasma membrane of Sertoli cells and affiliated endoplasmic reticulum3233.…”