TRANSFORMATIONS BETWEEN EPITHELIUM AND MESENCHYME - NORMAL, PATHOLOGICAL, AND EXPERIMENTALLY-INDUCED

In this review, we define the two major tissue types, epithelium and m esenchyme, and we describe the transformations (transdifferentiations) of epithelium to mesenchyme (EMT) and mesenchyme to epithelium (MET) that occur during embryonic development, The differentiation of the me tanephric blastema provides a striking example of MET, Differentiation of metanephric epithelium is promoted by matrix molecules and recepto rs (nidogen, laminins, alpha 6 integrins), hepatic growth factor/scatt er factor, and products of the genes wnt-1, wnt-4, and Pax-2, Transfor mation of MDCK epithelium to mesenchyme-like cells is promoted in vitr o by antibodies to E-cadherin, products of v-src, v-ras, and v-mos, an d by manipulation of the epithelium on collagen gels. Suspension in co llagen gel, transforming growth factors, and c-fos have also been show n to promote EMT in epithelia. We present studies from our laboratory showing that alpha 5 beta 1 integrin has a role in the EMT of lens epi thelium that is brought about by suspension in collagen gel, Our labor atory has also shown that transfection with the E-cadherin gene induce s embryonic corneal fibroblasts to undergo MET and that this MET is en hanced by interaction of the differentiating epithelium with living fi broblasts, This review calls attention to the roles that EMT and MET m ight have in kidney pathologies and urges further study of the involve ment of these phenomena in renal development, renal injury, and renal malignancy. (C) 1995 by the National Kidney Foundation, Inc.