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Lara Sabrina Carroll; Hoxc8 misexpression prevents embryonic eyelid fusion and transforms cornea and conjunctiva into keratinized skin. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3856.
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© ARVO (1962-2015); The Authors (2016-present)
Hox gene expression is excluded from the developing eye, although several members of this gene family are expressed in fetal and adult epidermis. We found that misexpression of Hoxc8 throughout mouse embryonic ectoderm results in pups born with their eyes open (eyes open at birth-EOB), and the cornea and conjunctiva transformed into a skin-like, keratinized epidermis. We examined expression of essential genes for eyelid fusion and corneal and conjunctival development to determine how Hoxc8 expression hijacks these specific epithelial programs to initiate epidermal development.
Mice carrying a conditional CAGGSHoxc8iresEGFP cassette were bred to Wnt6cre mice to create double heterozygous offspring that misexpress Hoxc8 throughout the Wnt6 domain, which is expressed broadly across the embryonic ectoderm. Pregnant dams were sacrificed to collect offspring between E11.5 and birth for phenotypic characterization. Tissue was collected for RNA and immunohistochemical analysis of genes involved in eyelid fusion pathways and corneal differentiation, including: Wnt, Bmp, Shh, Fgf10, ERK, and retinoic acid signaling, as well as Pax6 and various cytokeratin markers.
Newborn H&E staining showed sloughing squamous epithelium covering the cornea and conjunctiva of conditional mutants, with aberrant hair follicles present in the conjunctiva. Examination of earlier timepoints showed that mutants fail to develop an eyelid fusion front with associated migrating periderm and aligned F-actin fibers. Mutant eyelid tips lacked localized expression of p-cJun, p-ERK, Shh, Bmp4, and failed to downregulate Wnt signaling in contrast to age-matched control embryos. Conversely, mutant corneal epithelium failed to upregulate Wnt signaling, as evidenced by the lack of Lef1. Pax6, which is essential for maintaining corneal epithelium, was absent in mutant corneas, while skin specific keratins, K1 and K10 were upregulated throughout the corneal and conjunctival epithelium.
Emerging evidence suggests that Hox genes play a key role in regionalization of the skin and epidermal organs. Aberrant expression of Hoxc8 in the developing eye field ectoderm aborts Pax6 expression in corneal epithelium, leading to corneal and conjunctival keratinization, and disrupts most known signaling pathways for eyelid fusion, the last major morphogenetic event to occur in mammalian eye development.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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