Identification of multiple claudins in the rat epididymis

The luminal environment of the epididymis is highly specialized with specific proteins, ions, pH, etc. required for sperm maturation. Tight junctions between epididymal principal cells are responsible for the formation of the blood-epididymal barrier, which regulates this luminal environment. Claudins (Cldns) are a recently discovered family of transmembrane proteins and are essential components of tight junctions. Previous work from our laboratory has demonstrated the presence and localization of Cldn-1 in all regions of the rat epididymis. The objective of this study was to determine the presence and localization of other Cldns in the epididymis. Using RT-PCR we have identified mRNA transcripts for Cldn-3 through -9 in each region of the adult rat epididymis. Immunolocalization of Cldn-3, Cldn-4, and Cldn-5 were done in adult as well as in 42- and 14-day-old rats. Cldn-5 in adult rats was localized exclusively in blood vessels of the interstitium. Cldn-3 was localized apically in the epididymal epithelium between adjacent principal cells throughout the epididymis, where tight junctions have been reported histologically. There were no differences in the localization of Cldn-3 in epididymides of rats at the different ages. In 14-day-old rats, Cldn-4 was localized all along the lateral plasma membrane between adjacent principal cells. The immunostaining was more pronounced in the proximal regions of the epididymis. In both 42-day-old rats and adults, Cldn-4 was localized primarily to apical tight junctions between principal cells and staining was more pronounced in the proximal region of the epididymis. Cldn-16 transcripts were also identified by RT-PCR. These transcripts were present in both proximal and distal regions of the epididymis of young (Day 14 and 21) animals, but only in the proximal (initial segment) region of the adult epididymis. These data indicate that epididymal tight junctions are composed of several Cldns, suggestive of a complex regulation of the blood-epididymal barrier.