Branching morphogenesis is a key developmental process which requires exquisite regulation in order to successfully generate a variety of important tissues such as the lung, kidney, mammary gland and circulatory system. How this process is promoted and regulated to such an incredible degree is only beginning to be understood. One important player in this complex process is the fibroblast growth factor (FGF) receptor signalling pathway which has been shown conclusively to regulate branching morphogenesis in both the Drosophila tracheal system, and the mammalian lung. Evidence is emerging that this pathway is a conserved method of regulating branching, and that is may also function in other tissues. Murine mammary epithelial cells are also stimulated to undergo branching morphogenesis in vitro by FGF family members, and also by matrix metalloproteinases (MMPs). The aim of my project is to identify the role of FGFs, downstream signalling molecules and MMPs in regulating branching morphogenesis of the murine mammary gland, and to determine the relationship between FGF and MMP mediated branching. Firstly, the expression pattern of genes involved in the FGF pathway will be determined by RT-PCR and RNA in situ hybridisation in murine mammary tissue, initially concentrating of Fgf-10, Sprouty and Dof. The next step is to determine the function of these genes, and their role in branching morphogenesis using a variety of in vitro and in vivo assays which will also allow the relationship between genes and between signalling pathways to be studied. The effect of MMPs in isolation and in combination with those of FGFs can be analysed using recombinant proteins, transgenically modified cells and transgenic animals, to discover the relationship between these two inducers of epithelial branching. Finally, by grafting various combinations of wild-type, mutant and transgenic epithelium and/or stroma, I can identify the specific roles but the epithelium and the stroma have in regulating branching.