Molecular dynamics of the blood-testis barrier components during murine spermatogenesis

The blood-testis barrier (BTB) separates the seminiferous epithelium into the adluminal and basal compartments. During murine spermatogenesis, preleptotene/leptotene spermatocytes migrate from the basal to the adluminal compartment through the BTB during stages VIII-IX. In the present study, we focused on the tight junction (TJ) molecules and analyzed their spatiotemporal expression during the murine seminiferous epithelial cycle. Structural analysis revealed that the principal components of the BTB, for example, claudin-3, claudin-11, occludin, and zonula occludens-1 (ZO-1), were localized at the basal and luminal sides of the preleptotene/leptotene spermatocytes during the migration stages (VIII-IX). Although we detected claudin-11, occludin, and ZO-1 throughout spermatogenesis, claudin-3 was only detected during stages VI-IX. Quantitative PCR using dissected seminiferous tubules from three stages (Early: II-VI, Middle: VII-VIII, Late: IX-I) clarified that the mRNA levels of TJ molecules were not correlated with the histoplanimetrical protein levels during spermatogenesis. Additionally, tubulobulbar complexes, considered to be involved in the internalization of TJ, were observed at the BTB site. Furthermore, a significant reduction in the mRNA levels of genes for the degradation of occludin (Itch) and endocytic recycling (Rab13) were observed during the Late and Middle stages, respectively. Therefore, we hypothesized that the lag between mRNA and protein expression of TJ molecules may be due to posttranslational modulation, for example, tubulobulbar complexes and endocytic recycling processes. In conclusion, these findings indicate that the integrity of the BTB is maintained throughout spermatogenesis, and the stage-specific localization of claudin-3 protein plays an important role in regulating BTB permeability.