Fine structural aspects of the urothelium in the mouse ureter with special reference to cell kinetics

The present study aimed at clarifying the cell kinetics of the mouse ureteral epithelium by focusing on vesicle maturation in the cells and labeling with bromodeoxyuridine (BrdU). Electron microscopically, superficial cells were characterized by concave plaques in the apical plasma membrane and numerous fusiform vesicles in the cytoplasm. Intermediate cells were laden with ellipsoid vesicles, and basal cells had a few or no round vesicles. From the difference in number and form of vesicles among the three types of cells, it can be inferred that intermediate cells are immature in comparison with superficial cells, and likewise basal cells in comparison with intermediate cells. When BrdU was injected intraperitoneally once a day for seven days, most BrdU-labeled cells were located in the basal layer. Twelve days after the last injection, BrdU was detected in the intermediate or superficial layer in addition to the basal layer. These findings suggest that the basal cell is a progenitor cell giving rise to daughter cells that migrate upward to replace intermediate and superficial cells.