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- Eye formation in the human embryo begins at approximately three weeks into embryonic development and continues through the tenth week. Cells from both the mesodermal and the ectodermal tissues contribute to the formation of the eye. Specifically, the eye is derived from the neuroepithelium, surface ectoderm, and the extracellular mesenchyme which consists of both the neural crest and mesoderm. Neuroepithelium forms the retina, ciliary body, iris, and optic nerves. Surface ectoderm forms the lens, corneal epithelium and eyelid. The extracellular mesenchyme forms the sclera, the corneal endothelium and stroma, blood vessels, muscles, and vitreous. The eye begins to develop as a pair of optic vesicles on each side of the forebrain at the end of the 4th week of pregnancy. Optic vesicles are outgrowings of the brain which make contact with the surface ectoderm and this contact induces changes necessary for further development of the eye. Through a groove at the bottom of the optic vesicle known as choroid fissure the blood vessels enter the eye. Several layers such as the neural tube, neural crest, surface ectoderm, and mesoderm contribute to the development of the eye. Eye development is initiated by the master control gene PAX6, a homeobox gene with known homologues in humans (aniridia), mice (small eye), and Drosophila (eyeless). The PAX6 gene locus is a transcription factor for the various genes and growth factors involved in eye formation. Eye morphogenesis begins with the evagination, or outgrowth, of the optic grooves or sulci. These two grooves in the neural folds transform into optic vesicles with the closure of the neural tube. The optic vesicles then develop into the optic cup with the inner layer forming the retina and the outer portion forming the retinal pigment epithelium. The middle portion of the optic cup develops into the ciliary body and iris. During the invagination of the optic cup, the ectoderm begins to thicken and form the lens placode, which eventually separates from the ectoderm to form the at the open end of the optic cup. Further differentiation and mechanical rearrangement of cells in and around the optic cup gives rise to the fully developed eye. (en)
- O desenvolvimento do olho é um processo evolutivamente conservado em vertebrados, sendo regulado por fatores de transcrição expressos de maneira dinâmica, com padrões de sobre-expressão que regulam uns aos outros.O processo se inicia entre a gastrulação e a organogênese,envolvendo células tanto da ectoderme, especificamente o neuroepitélio e a ectoderme superficial, quanto mesénquima extracelular.O neuroepitélio é responsável pela formação da retina, corpos ciliares e a retina, enquanto a ectoderme de superfície forma o cristalino, a córnea e as pálpebras.O mesénquima forma a esclera, o endotélio da córnea, os vasos sanguíneos e a musculatura associada.O organismo modelo no qual o processo é mais amplamente estudado é Xenopus laevis. (pt)
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| rdfs:comment
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- O desenvolvimento do olho é um processo evolutivamente conservado em vertebrados, sendo regulado por fatores de transcrição expressos de maneira dinâmica, com padrões de sobre-expressão que regulam uns aos outros.O processo se inicia entre a gastrulação e a organogênese,envolvendo células tanto da ectoderme, especificamente o neuroepitélio e a ectoderme superficial, quanto mesénquima extracelular.O neuroepitélio é responsável pela formação da retina, corpos ciliares e a retina, enquanto a ectoderme de superfície forma o cristalino, a córnea e as pálpebras.O mesénquima forma a esclera, o endotélio da córnea, os vasos sanguíneos e a musculatura associada.O organismo modelo no qual o processo é mais amplamente estudado é Xenopus laevis. (pt)
- Eye formation in the human embryo begins at approximately three weeks into embryonic development and continues through the tenth week. Cells from both the mesodermal and the ectodermal tissues contribute to the formation of the eye. Specifically, the eye is derived from the neuroepithelium, surface ectoderm, and the extracellular mesenchyme which consists of both the neural crest and mesoderm. Further differentiation and mechanical rearrangement of cells in and around the optic cup gives rise to the fully developed eye. (en)
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