The effect of lamina propria on the growth and differentiation of urothelial cells in vitro.

The effect of lamina propria on the growth and differentiation of the mouse urinary bladder urothelial cells in vitro has been studied by light and electron microscopy using morphological and immunohistochemical methods. Three different types of urothelial cultures were maintained on a porous membrane in serum-free medium for 10 days. Our results showed that urothelial cells in culture types I and II were organised as the multilayer epithelium showing terminal differentiation, from the porous membrane toward the surface. On the surface of culture type I and II, superficial urothelial cells were highly differentiated. They formed tight junctions and had plaques of an asymmetric unit membrane, a hallmark of terminal differentiation in bladder superficial cells. These cultured superficial cells were also cytokeratin 20 positive. On the contrary, urothelial cells in culture type III have shown a limited capacity for survival and have grown as poorly differentiated monolayer. These results revealed that reciprocal intercellular signalling between the lamina propria and urothelial cells is essential to achieve terminal differentiation of urothelial cells in vitro.