Gene-environment interactions in epithelial morphogenesis

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Project Summary/Abstract The dioxin-like chemicals (DLCs) are global environmental pollutants that pose a significant health threat to humans. It is widely believed that the genetic make-up is a major determinant of disease risk from exposure, but the actual gene-environment mechanisms that predispose individuals to disease are poorly understood. We have developed a mouse model to investigate gene mutations that sensitize developmental tissues to dioxin toxicity. The model is based on embryonic eyelid closure, a developmental process conserved in all mammals. Eyelid closure is a major morphogenetic event occurring in late embryogenesis, driven by forward movement of the eyelid epithelial cells leading to fusion of the opposing eyelids. Failure of eyelid closure is not life threatening but results in an eye open at birth (EOB) phenotype in the newborns. The EOB phenotype is easy to spot, and consequently is found in a large number of genetic mutant strains. Over the years, the EOB mice serve as a powerful tool to elucidate the genetic network and signaling mechanisms underlying epithelium morphogenesis. Building on this model, we have identified the MAP3K1-JNK signaling cascades in the regulation of eyelid closure. We recently applied this system to investigate the genetic susceptibility to environmental chemical toxicity, and showed that the combination of Map3k1 gene heterozygosity and in utero dioxin exposure blocks eyelid closure whereas neither condition alone has a detrimental effect. These observations suggest that eyelid closure defect can be a multifactorial disorder resulting from gene-environment (GxE) interactions. The current proposal will investigate in three Specific Aims the mechanisms of GxE interactions by testing the hypothesis that genetic and environmental stresses converge on repression of the MAP3K1-JNK pathway to disrupt epithelial morphogenesis. Aim 1 will determine the molecular link between the dioxin signals and the MAP3K1- JNK pathways. Guided by preliminary findings, we will test whether the EGFR pathway mediates the crosstalk between these signals in eyelid development. Results will define a novel mechanism where the genetic and environmental factors target separate signaling pathways, but the crosstalk of the pathways leads to adverse outcomes. Aim 2 will identify novel genetic components of the MAP3K1 pathway in dioxin toxicity. Results will lead to a mechanistic understanding of the genetic conditions susceptible to chemical toxicity. Aim 3 will bridge the gap between basic and translational research by taking advantage of the identification of MAP3K1 heterozygosity in a patient with congenital eye structural abnormalities. We will use patient-specific induced pluripotent stem cells (iPSCs) to examine whether dioxin treatment during in vitro differentiation leads to inactivation of MAP3K1 signaling and impaired epithelial cell migration, which are biological endpoints linked to defective eyelid closure. Results will bring us a step closer to translate mechanistic discoveries in mice to understanding human diseases. Studies proposed in this project will provide critical insights into the mechanisms of GxE interactions and an experimental paradigm to study multifactorial etiology underlying birth defects.