Cell-adhesion molecule uvomorulin during kidney development.

We studied the expression of a cell adhesion molecule during morphogenesis of the embryonic kidney. The 120-kDa glycoprotein, called uvomorulin, is known to be present on a number of epithelia. During the development of the kidney, a mesenchyme is converted into an epithelium when it is properly induced. The uninduced mesenchyme did not express uvomorulin, as judged by immunofluorescence and immunoblotting using previously characterized antibodies. Uvomorulin does not appear in the mesenchyme as a direct consequence of induction. Rather it becomes detectable approximately 12 hr after completion of induction, at 30-36 hr in vitro when the cells adhere to each other. Distinct differences in uvomorulin expression were seen in the different parts of the nephron. In the mesenchymally derived epithelia (glomeruli, tubules), uvomorulin could be detected only in the tubules, whereas the epithelium of the glomeruli remained negative at all stages of development. Our embryonic studies show that these differences arise very early, as soon as the different parts of the nephron can be distinguished morphologically. It is likely that uvomorulin plays a role in the initial adhesion of the differentiating tubule cells. However, we failed to disrupt histogenesis by applying antibodies to the organ cultures of developing tubules although the antibodies penetrated the tissues well and bound to the differentiating cells.