Functional homology in teleost and mammalian epidermal morphogenesis
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The epidermis is a stratified epithelium that makes up the outermost component of the skin. During embryogenesis, this portion of the skin undergoes a complex series of transformations to reach a mature state and provide a protective barrier. Although many of the molecular regulators of this process have been identified, they are poorly understood. IRF6, 14-3-3σ, CHUK/IKKα, and Ovol1 knockout mutant mice all exhibit phenotypes involving hyperproliferative epidermal cells. The zebrafish maternal-effect mutant poky has a similar phenotype, exhibiting a hyperproliferative epidermal layer called the enveloping layer (EVL), as well as a delay in epiboly. The poky gene has been identified as the zebrafish homolog of CHUK/IKKα which has been described as a tumor suppressor. We hypothesized that the gene regulators of mammalian epidermal morphogenesis would be functionally conserved in zebrafish. If this were true, zebrafish could provide a simpler and more cost-effective model system for studying epidermal morphogenesis and mammalian squamous cell carcinoma development. An in situ hybridization assay using zebrafish wild-type and poky mutant embryos was designed to examine expression patterns of these genes. Of the embryos that showed expression, none of them showed characteristic EVL expression suggesting that these genes do not play a role in zebrafish epidermal morphogenesis. Therefore, these genes do not appear to be functionally conserved between mice and zebrafish. Also, in order to investigate the role of IKK2 more closely, and determine if CHUK and IKK2 are functionally redundant, we planned to inject mRNA made from the full-length ikk2 gene into the poky embryos in attempt to rescue the phenotype; however, the cloning process of ikk2 was unsuccessful and no rescue attempt was made.