THE EFFECT OF EPIDERMAL GROWTH-FACTOR AND TRANSFORMING-GROWTH-FACTOR BETA(1) ON PROLIFERATION AND DIFFERENTIATION OF UROTHELIAL CELLS IN URINARY-BLADDER EXPLANT CULTURE

The effects of two growth factors, EGF and TGF beta 1, on growth and d ifferentiation of different populations of urothelial cells in explant cultures of mouse urinary bladder have been studied by electron micro scopy and lectin analysis. Ln an explant culture 10 days after the imp lantation three different populations of urothelial cells can be disti nguished. Original urothelial cells, which are integral part of the ex plant, new urothelial cells, which cover the base-lateral sides of the explant and are organized in a multilayer epithelium, and new urothel ial cells, which are not any more in direct contact with, the explant and grow over the membrane in epithelium-like structure. Exogenously a dded EGF or TGF beta(1) did not affect either the formation or the thi ckness of multilayered urothelium, so cells were proliferating on the free surfaces of stroma as well as on the epithelium expanding over th e membrane. In the absence of growth factors in medium, the newly form ed base-lateral multilayered epithelium bordering the stroma shows ult rastructural signs of terminal differentiation suggesting that for cel l proliferation and differentiation the action of stroma is of crucial importance. On the other hand, the differentiation of the epithelium spreading over the membrane, but not its thickness, is affected by exo genously added TGF beta(1). Solely in TGF beta(1)-treated cultures a d ifferentiation similar to that in vivo takes place. The apoptosis of t he urothelial cells was not increased by TGF beta(1). The lectin analy sis by WGA and ConA conjugated with ferritin revealed that ConA-ferrit in combines only with the surface cells which grow over the membrane i n the absence of TGF beta(1).