The molecular mechanisms governing mammalian development are thought to involve signal transduction pathways, that is the transfer of information from signals in the external environment to regulators of gene expression and activity within the cell. The ocular lens has long been a model system for studying morphogenesis, specifically in demonstrating (1) the importance of spatial position to the differentiation potential of cells within a developing organ and (2) the importance of inductive responses, potentially mediated by growth factor action, to regulation of this process. In vitro studies on lens cell differentiation primarily in the chick and rat have implicated insulin, insulin-like growth factor-1 and basic fibroblast growth factor as putative extracellular inducers of lens fiber cell differentiation. This proposal describes experiments designed to study the roles of these growth factors in lens development using the mouse as a model system. First, to identify which growth factors are implicated in mouse lens development, the expression and activity of growth factor receptors in the lens will be analyzed by immunohistochemistry and in situ hybridization. Secondly, the responsiveness of the mouse lens epithelial cell type to these growth factors will be characterized. And third, strategies for manipulating the lens cell's susceptibility to growth factors will be analyzed in tissue culture. These strategies will include increasing growth factor response by overexpression of the growth factor or its receptor and inhibiting growth factor response by overproducing mutant receptors which act as trans-dominant repressors of endogenous receptors. Based upon the information obtained from these in vitro studies, transgenic mice will be generated for the purpose of altering growth factor response in the lens during its development. Through this approach, the role of these growth factors in embryonic induction will be directly tested in an animal model system using approaches that permit one to alter growth factor response of a specific tissue in vivo. The potential success of this proposal is based in part on the investigator's extensive experience in successfully targeting transgenes to the mouse ocular lens at appropriate times in lens development, in part on the investigator's successful establishment of epithelial cell lines from these transgenic mice, and in part on the insights the investigator's have derived from studying growth factor response in these mouse lens epithelial cells. The studies proposed here should provide a sound basis for determining if insulin, IGF-1 or bFGF play a determinative role in the induction of lens fiber cell differentiation.
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