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Morphogenesis of the anterior segment in the zebrafish eye

DOI: 10.1186/1471-213x-5-12

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As in other vertebrates, the zebrafish anterior segment derives from diverse origins including surface ectoderm, periocular mesenchyme, and neuroepithelium. Similarly, the relative timing of tissue differentiation in the anterior segment is also conserved with other vertebrates. However, several morphogenic features of the zebrafish anterior segment differ with those of higher vertebrates. These include lens delamination as opposed to invagination, lack of iris muscles and ciliary folds, and altered organization in the iridocorneal angle. In addition, substantial dorsal-ventral differences exist within the zebrafish anterior segment.Cumulatively, our anatomical findings provide a reference point to utilize zebrafish for genetic studies into the mechanisms of development and maintenance of the anterior segment.The anterior segment of the vertebrate eye is comprised of the cornea, lens, iris, ciliary body, and highly specialized tissue at the iridocorneal angle. Two main functions are ascribed to the ocular anterior segment. The first is to focus incoming light onto the neural retina and the second is to regulate intraocular pressure. For mammals and other higher vertebrates, refraction of light entering the eye is accomplished by both the transparent cornea and lens. In many aquatic vertebrates, including fish, the lens is solely responsible for focusing incoming light [1,2]. In all vertebrates, intraocular pressure is maintained by the balance between aqueous humor production and outflow [3]. The dynamics of aqueous humor have been best characterized in mammals where ciliary epithelial cells produce the clear ocular fluid while the trabecular meshwork, which is situated at the iridocorneal angle overlying Schlemm's canal, regulates drainage.The structures of the anterior segment arise from diverse embryonic lineages and there is exquisite coordination among the different compartments during development. Studies in avian and mammalian species have shown that tissues


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