- Polycystin, the polycystic kidney disease 1 protein, is expressed by epithelial cells in fetal, adult, and polycystic kidney. Ward, C.J., Turley, H., Ong, A.C., Comley, M., Biddolph, S., Chetty, R., Ratcliffe, P.J., Gattner, K., Harris, P.C. Proc. Natl. Acad. Sci. U.S.A. (1996)