Zyxin, axin, and Wiskott-Aldrich syndrome protein are adaptors that link the cadherin/catenin protein complex to the cytoskeleton at adherens junctions in the seminiferous epithelium of the rat testis
Lee,Nikki P.Y.; Mruk,Dolores D.; Conway,Anne M.; Cheng,Chuen-yan
Journal of Andrology 25(2): 200-215
Publication date: 2004
During spermatogenesis, the movement of germ cells across theseminiferous epithelium is associated with extensive junctionrestructuring. Yet the underlying mechanism (or mechanisms)that regulates these events is largely unknown. If the moleculararchitecture of the cell-cell actin-based adherens junction(AJ), such as ectoplasmic specialization (ES) and tubulobulbarcomplex- two testis-specific AJ types, is known, manyfunctional mechanistic studies can be designed. We thus undertookan investigation to study 3 adaptors in the seminiferous epithelium:zyxin, axin, and Wiskott-Aldrich syndrome protein (WASP). All3 adaptors were shown to be products of Sertoli and germ cells.Zyxin was shown to be a stage-specific protein that was mostprominent during stages V-VII and restricted mostly topachytene spermatocytes, but it could also be detected at thesite of basal and apical ectoplasmic specialization (ES). Zyxin,axin, and WASP were shown to be structurally linked to theN-cadherin/ß-catenin/-actinin/actin complex but notto the nectin-3/afadin or the ß1-integrin-mediatedprotein complexes. Interestingly, zyxin, axin, and WASP arealso structurally linked to vimentin (an intermediate filamentprotein) and -tubulin (the subunit of a microtubule), whichsuggests that they have a role (or roles) in the regulationof the dynamics of the desmosome-like junction and microtubule.These results illustrate that zyxin, axin, and WASP are adaptorsin both AJs and intermediate filament-based desmosome-likejunctions. This raises the possibility that classic cadherinsare also associated with vimentin-based intermediate filamentsvia these adaptors in the testis. While virtually no N-cadherinwas found to associate with vimentin in the seminiferous tubules,it did associate with vimentin when testis lysates were used.Interestingly, about 5% of the E-cadherin associated with vimentinin isolated seminiferous tubules, and about 50% of the E-cadherinin the testis used vimentin as its attachment site. These datasuggest that cadherins in the testis, unlike those in otherepithelia, use different attachment sites to anchor the cadherin/catenincomplex to the cytoskeleton. The levels of zyxin, axin, andWASP were also assessed during AF-2364-mediated AJ disruptionof the testis, which illustrated a time-dependent protein reductionthat was similar to the trends observed in nectin-3 and afadinbut was the opposite of those observed for N-cadherin and ß-catenin,which were induced. Collectively, these results illustratethat while these adaptors are structurally associated withthe cadherin/catenin complex in the testis, they are regulateddifferently.