Transgenic mice that over express the proteoglycan agrin have severe defects in ocular development. It is our hypothesis that this gain-of-function agrin mutation is perturbing eye development by disrupting the normal functions of the extracellular matrix (ECM) in the developing eye. The phenotype is also strain dependent, occurring only in a C57BL/6 genetic background, but with complete penetrance in that strain. Therefore, we also hypothesize that C57BL/6 mice provide a sensitized background for this phenotype, and that identifying the genes underlying this sensitivity will be relevant to related human conditions. The phenotype of the agrin-transgenic mice ranges from complete anophthalmia to corneal opacities caused by a failure of the lens to separate from the cornea. Frequently observed phenotypes include severe colobomas, a failure of lens to form, and an infiltration of pigmented fibrovascular tissue into the eye. The transgenic protein localizes to same structures that are affected. Based upon the localization of the transgenic protein and an increase in eye defects in a second, independent transgenic founder (though only at thirty percent initial penetrance) we conclude that the phenotype is a direct result of the presence of the transgenic protein in the eye. However, the possibilities that the phenotype is caused by a non-specific fetal stress response or by a mutation created by the transgene insertion have not been formally ruled out. The first specific aim of this proposal is to make this determination using a combination of genetic and molecular approaches. The phenotype is strain dependent and C57BL/6 mice are prone to spontaneous ocular defects at a rate of approximately five percent. The agrin-transgenic phenotypes resemble the severe extremes of the spontaneous defects. C57BL/6 provides a sensitized background for studying eye development, and the agrin-transgenic construct exacerbates this sensitivity. The second specific aim of this proposal is to use the agrin-transgenic mice in a classic genetic mapping experiment to identify the loci in the C57BL/6 background that predispose this strain to ocular dysgenesis. The haracterization of agrin overexpression as a tool for exploring the role of the ECM will open many new avenues of research. In addition, the identification of genes predisposing these transgenic mice to eye defects will be of great benefit to studies linking signaling molecules, environmental factors and protein effectors in both mice and humans. ? ?
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