MESENCHYMAL-EPITHELIAL INTERACTIONS IN THE BLADDER

During bladder development, undifferentiated mesenchymal and epithelia l cells undergo an orderly sequence of differentiation defined by the expression of smooth-muscle (alpha-actin, myosin, vinculin, desmin, vi mentin, and laminin) and epithelial (cytokeratins 5, 7, 8, 14, 18 and 19) protein markers. This process requires mesenchymal-epithelial inte ractions with bladder epithelium (urothelium) necessary for the differ entiation of bladder smooth muscle. Peptide growth factors such as ker atinocyte growth factor (KGF) and transforming growth factors (TGF) al pha and beta are likely candidates as mediators of these mesenchymal-e pithelial interactions. Transcripts for KGF, TGF alpha, and TGF beta a re regulated during bladder development and during smooth-muscle hyper trophy secondary to bladder-outlet obstruction. Finally, two experimen tal bladder models - (1) partial outlet obstruction and (2) regenerati on of bladder smooth muscle into an acellular tissue matrix - are desc ribed in the context of mesenchymal-epithelial interactions in the bla dder.