Development of tight junctions in the caput epididymal epithelium of the mouse

The course of development of the epithelial tight junctions of the Wolffian duct and the caput epididymal principal cells in the mouse were examined by freeze-fracture. The histogenesis of the epididymis is briefly described. In the 12-day embryo, tight junction meshworks surround the entire circumference of the columnar cells in the juxtaluminal position. During fetal life, the strands are more discontinuous than those of postnatal mice, and two or more strands frequently run together. Up to 10 days of age, the basal compartments of the tight junctions are much larger than the luminal ones. Marked increases in both the number of strands and the depth of the tight junctions appear by 20 days. Strands with a terminal loop are often observed up to 16 days, except for the newborn stage, suggesting that the formation of the terminal loop is related to the active elongation of the strands. The tight junctions increase greatly in number and depth near three-cell junctions. Up to 20 days, the strands anastomose frequently, with no particular orientation to the cell axis. After 20 to 37 days, the direction of the strands becomes parallel to the luminal surface, with a decreased number of anastomoses as the lumen widens. In the adult, the number of sealing strands is about 10 within the depth of the tight junctions. Free-ended strands are seen in all stages examined. The formation of the tight junction meshworks is discussed in the light of the findings during the development.