(Taken directly from the application) The kidney forms by a series of reciprocating interactions between two compartments, the ureteric bud and mesenchyme. The ureteric bud signals the mesenchyme to proliferate and epithelialize, while the mesenchyme signals the ureter to invade and branch. The results is a unit, composed of proliferating mesenchymal cells located along the stalks of the ureter. This unit is stereotyped in architecture and reproduced with the formation of each nephron. To identify ureteric molecules that regulate mesenchymal development, I have prepared cell lines from the ureteric bud (UB cells). These cells express all the known characteristics of the native ureter. Using UB cells and dissected mesenchymes for co-culture, we discovered that induction is composed of two distinct signaling mechanisms. UB cells trigger mesenchymal growth by secreting soluble proteins, while they induce conversion with cell associated molecules. In fact, the cells express multiple proteins with each activity. I have recently discovered that UB cells produce at least six distinct mesenchymal mitogens; and have now identified two as authentic ureteric proteins, basic FGF (basic fibroblast growth factor) and tissue inhibitor of metalloproteinase-2 (TIMP-2). The latter is a protease inhibitor that we discovered acts as a novel mesenchymal growth factor. In addition, by using UB cells as antigen for monoclonal production, I have isolated antibodies that recognize the basolateral membrane or basement membrane of the embryonic ureter and block induction. I propose to identify the group of ureteric proteins that control mesenchymal proliferation and conversion to epithelia. Isolation of growth factors by classical biochemical methodology and cell associated proteins using monoclonal antibodies that were selected for their neutralizing activities, are methods that have been successful in our laboratory. Further, I propose to find how the activity of these molecule is localized, so that they locally and repetitively generate units of mesenchyme and a branch of ureter. I propose that the mesenchyme itself regulates the expression, secretion and degradation of ureteric signaling proteins. In fact, the same mesenchymal proteins that stimulate ureteric branching may regulate ureteric signals that stimulate the mesenchyme. Thus, the identification of ureteric signaling molecules and their regulation by mesenchyme will demonstrate how mesenchymal and ureteric development are coordinated and seek to explain the organization of the mesenchymal-epithelial unit.
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