Breast cancer resistance protein regulates apical ectoplasmic specialization dynamics stage specifically in the rat testis.

Drug transporters determine the bioavailability of drugs in the testis behind the blood-testis barrier (BTB). Thus, they are crucial for male contraceptive development if these drugs (e.g., adjudin) exert their effects behind the BTB. Herein breast cancer resistance protein (Bcrp), an efflux drug transporter, was found to be expressed by both Sertoli and germ cells. Interestingly, Bcrp was not a component of the Sertoli cell BTB. Instead, it was highly expressed by peritubular myoid cells at the tunica propria and also endothelial cells of the microvessels in the interstitium at all stages of the epithelial cycle. Unexpectedly, Bcrp was found to be expressed at the Sertoli-step 18-19 spermatid interface but limited to stage VI-early VIII tubules, and an integrated component of the apical ectoplasmic specialization (apical ES). Apparently, Bcrp is being used by late-stage spermatids to safeguard their completion of spermiogenesis by preventing harmful drugs to enter these cells while they transform to spermatozoa. Also, the association of Bcrp with actin, Eps8 (epidermal growth factor receptor pathway substrate 8, an actin barbed end capping and bundling protein), and Arp3 (actin-related protein 3, a component of the Arp2/3 complex known to induce branched actin polymerization) at the apical ES suggest that Bcrp may be involved in regulating the organization of actin filament bundles at the site. Indeed, a knockdown of Bcrp by RNAi in the testis perturbed the apical ES function, disrupting spermatid polarity and adhesion. In summary, Bcrp is a regulator of the F-actin-rich apical ES in the testis.