During the past grant period we cloned several new receptor tyrosine kinases and phosphatases from the lens epithelium, provided evidence that the central lens epithelium is not an important source of nutrients for the underlying lens fibers, demonstrated that cAMP controls lens fiber cell elongation by regulating the phosphorylation of a membrane potassium channel, showed that a recently-discovered receptor signaling pathway is important in controlling lens cell proliferation and provided evidence for a new stage in the differentiation of lens fiber cells. In the next grant period we will extend our studies of growth factor receptors and their signalling pathways in lens epithelial cells. The importance of the JAK- STAT pathway in controlling lens cell proliferation will be established. These studies will employ cultured lens cells and western blot assays for STAT1 and phosphotyrosine. The redistribution of STAT1 in lens cells following growth factor stimulation will be determined by confocal microscopy. The function of the IGF, FGF and PDGF receptors in the lens will be analyzed using retroviruses to deliver """"""""dominant-negative"""""""" constructs of these receptors to lens cells in vivo. Similar methods will be used to determine the function of two """"""""orphan"""""""" receptors, c-axl, and a new receptor discovered in our laboratory, M2. We will also extend our studies of changes during lens fiber formation of cytoskeletal-adhesion proteins to adult chicken, monkey and human lenses. These studies will be performed by confocal microscopy and immunocytochemistry. Specific alterations in the organization of cells, cell adhesion proteins and the lens cell cytoskeleton will be identified in human cortical cataracts. The major phosphotyrosine-containing proteins in lens adherens junctions will be identified. The role of hydrogen peroxide in regulating the phosphorylation of these proteins and the cell-substrate adhesion of lens epithelial cells will be determined. We will continue to identify and map the distribution of lens phosphatases, as these are likely targets for H2O2 in the lens. Finally, we will examine the formation of cataracts in the lenses of humans and mice having a defect in the gene responsible for the human disease, neurofibromatosis 2 (NF2). The NF2 gene codes for a tumor suppressor and defects in this gene cause CNS tumors and posterior subcapsular cataracts. Other experiments will determine the role of merlin, the protein encoded by the NF2 gene, in cataract formation. Mouse lenses from animals with one defective NF2 gene will be used to determine whether accumulated DNA damage is the cause of several kinds of cataracts.
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