Myosin VIIa Supports Spermatid/Organelle Transport and Cell Adhesion During Spermatogenesis in the Rat Testis

The biology of transport of spermatids and spermatid adhesion across the seminiferous epithelium during the epithelial cycle remains largely unexplored. Nonetheless, studies have implicated the role of motor proteins in these cellular events. In this article, we report findings to unravel the role of myosin VIIa, an F-actin-based barbed (+)-end-directed motor protein, to support cellular transport and adhesion in the testis. Using RNA interference to knock down myosin VIIa in Sertoli cells cultured in vitro as a study model was shown to perturb the Sertoli cell tight junction permeability barrier, mediated through disorganization of actin- or microtubule (MT)-based cytoskeletons owing to disruptive changes on the spatiotemporal expression of F-actin or MT-regulatory proteins. Consistent with these in vitro findings, knockdown of myosin VIIa in the testis in vivo also induced disorganization of the actin- and MT-based cytoskeletons across the seminiferous epithelium, mediated by disruptive changes in the spatiotemporal expression of actin- and MT-based regulatory proteins. More important, the transport of spermatids and organelles across the epithelium, as well as cell adhesion, was grossly disrupted. For instance, step 19 spermatids failed to be transported to the adluminal compartment near the tubule lumen to undergo spermiation; in this manner, step 19 spermatids were persistently detected in stage IX and XII tubules, intermingling with step 9 and 12 spermatids, respectively. Also, phagosomes were detected near the tubule lumen in stage I to III tubules when they should have been degraded near the base of the seminiferous epithelium via the lysosomal pathway. In summary, myosin VIIa motor protein was crucial to support cellular transport and adhesion during spermatogenesis.