Rat Seminiferous Epithelium Contains a Unique Junction (Ectoplasmic Specialization) with Signaling Properties Both of Cell/Cell and Cell/Matrix Junctions

Abstract

The seminiferous epithelium contains unique actin related cell-cell junctions, termed ectoplasmic specializations (ESs). Turnover of these junctions is fundamental to sperm release and to movement of spermatocytes from basal to adluminal compartments of the epithelium during spermatogenesis. In this study we report several novel observations related to the spatial and temporal distribution of integrin-related signaling molecules at ESs. We confirm the presence of beta(1)-integrin at these sites and further demonstrate co-localization of integrin linked kinase (ILK). beta(1)-Integrin and ILK were shown by immunoprecipitation to associate in whole cell lysates of seminiferous epithelium. This observation provides the first evidence for a direct beta(1)-integrin/ILK interaction in noncultured epithelium. Pan-cadherin and beta-catenin antibodies did not react at ESs. Rather, antibodies reacted with desmosome-like junctions that are present both at basal junctional complexes between Sertoli cells and at sites of attachment to spermatogenic cells. Focal adhesion kinase (FAK), a known integrin-associated molecule, did not codistribute with beta(1)-integrins and did not associate with these adhesion molecules in immunoprecipitation studies. Although FAK was expressed in the epithelium, it appeared to be limited to the cytoplasm of early spermatogenic cells. Significantly, polyclonal antibodies against phosphotyrosine-containing residues reacted strongly at ESs, with highest levels detected during sperm release and turnover of basal junction complexes. Our observations indicate that ESs share cell signaling features both of cell-cell junctions and of cell-extracellular matrix junctions.

Anchoring Junctions As Drug Targets: Role in Contraceptive Development

“…Nevertheless, it is interesting to note that there are no reported cases of hemidesmosome disassembly in the testis, suggestive of stable and robust adhesion. Moreover, ␣6␤1 integrin does not seem to localize to the intermediate filament-based hemidesmosome in the testis but apparently to the actin-based basal ectoplasmic specialization (Chapin et al, 2001;Mulholland et al, 2001). In addition, except for a single report published nearly 2 decades ago that described the presence of an uncharacterized 120-kDa protein in the testis referred to as 1-2B7B (Zhang et al, 1991), there has been no advancement in the biology of the hemidesmosome in this organ.…”

“…Generally speaking, numerous studies have linked focal contact function to cell spreading and migration. Although the existence of focal contacts in the testis has never been described, several studies from different laboratories have reported the presence of putative focal contact proteins in this organ, including ␣6␤1 integrin (Salanova et al, 1995(Salanova et al, , 1998Mulholland et al, 2001), integrin-linked kinase [ILK (Mulholland et al, 2001)], focal adhesion kinase [FAK (Siu et al, 2003)], c-Src Zhang et al, 2005), vinculin (Grove et al, 1990;Pfeiffer and Vogl, 1991), profilin III (Braun et al, 2002), talin (Santoro et al, 2000), paxillin (Wine and Chapin, 1999), zyxin , fimbrin (Grove and Vogl, 1989), and laminin (Koch et al, 1999;Siu and Cheng, 2004a;Yan and Cheng, 2006). It is noteworthy that many of these focal contact proteins were shown to localize to the ectoplasmic specialization rather than at the Sertoli cell-basement membrane interface, as expected.…”

“…So far, a growing list of proteins has been shown to underlie ectoplasmic specialization function including ␣6␤1 integrin (Palombi et al, 1992;Salanova et al, 1995;Mulholland et al, 2001), laminin , actin (Vogl et al, 1993), ␣-actinin (Russell and Goh, 1988), myosin VIIA (Hasson et al, 1997), fimbrin (Grove and Vogl, 1989), espin (Bartles et al, 1996), vinculin (Grove et al, 1990;Pfeiffer and Vogl, 1991), phosphorylated c-Src , paxillin (Mulholland et al, 2001), gelsolin , cadherin , ILK (Mulholland et al, 2001), phosphorylated FAK (Siu et al, 2003), testin (Grima et al, 1998), and Keap1 Velichkova et al, 2002) (Fig. 1).…”

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

“…␤1-Integrin and ␣6-integrin form a functional adhesion complex of ␣6␤1-integrin at the apical ES residing in Sertoli cells (9,10,15), and ␣6␤1-integrin is the receptor of laminin-333 residing in elongating/elongated spermatids (3,11). However, the precise localization of ␤1-integrin at the basal compartment is not well defined.…”

“…For instance, ␤1-integrin was reported to be a component of the basement membrane in the seminiferous tubules (14), perhaps at the hemidesmosomes. Others have reported its localization with the actin-based anchoring junction structure (i.e., basal ES) at the BTB (10,15). It is also not known whether there is cross-talk between ␤1-integrin in the apical ES, the BTB, and hemidesmosome.…”