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Y. Xia, L. Zhang, J.V. Jester, W.W. Kao; Role of MEK Kinase 1 in Mouse Eyelid Morphogenesis . Invest. Ophthalmol. Vis. Sci. 2003;44(13):647.
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Purpose: Embryonic eyelid closure is essential for vertebrate eye development, its defect in mice results in eye-open at birth (EOB) phenotype that often leads to severe eye pathology. Mice deficient in MEK Kinase 1 (MEKK1), a cytoplasmic protein kinase and an upstream regulator of the mitogen activated protein kinase (MAPK) pathways, exhibit EOB. This study is undertaken to understand the molecular mechanisms and signaling pathways by which MEKK1 regulates eyelid morphogenesis. Methods: Eye sections of wild type and MEKK1-null fetuses were analyzed by histological methods. Whole mount phalloidin staining was carried out on eye tissues of E15.5 fetuses and F-actin formation was observed by Con-focal microscopy. Epithelial cells expressing active or kinase-inactive MEKK1 were examined for F-actin formation, JNK activation and c-Jun N-terminal phosphorylation. A role of MEKK1 in epithelium migration was evaluated in vitro by measurement of wound healing of keratinocytes-derived from wild type and MEKK1-deficient mice. MEKK1 signaling regulated gene expression was identified using cDNA microarray analyses of keratinocytes and of developing eyelid tissues isolated from wild type and MEKK1-deficient mice. Results:Mice deficient in MEKK1 exhibit EOB due to impairment in embryonic eyelid closure. The abundant MEKK1 expression in developing tip of eyelid epithelium suggests that it functions in this tissue. Eyelid epithelium of wild type fetus displays prominent F-actin formation, whereas MEKK1-deficient mice exhibit reduced actin polymerization in eyelid epithelium. Expression of active, but not kinase inactive, MEKK1 causes an induction of prominent actin stress fibers in epithelial cells. MEKK1 activity correlates to JNK activation and cJun N-terminal phosphorylation and a specific JNK inhibitor abolishes actin polymerization induced by MEKK1. A role of MEKK1 in epithelium movement is demonstrated by in vitro scratch assay. Keratinocytes isolated from MEKK1-deficient mice show a delayed wound healing comparing to the cells from mice that have one functional Mekk1 allele. cDNA microarray studies suggest that some effects of MEKK1 in eyelid development are due to changes in gene expression in eyelid epithelium. Conclusions: MEKK1 regulates JNK activation, cJun phosphorylation and actin polymerization in epithelial cells and in developing eyelid epithelium that are pertinent to embryonic eyelid closure. MEKK1-regulated pathway may control eyelid morphogenesis through regulation of gene expression.
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