Classical transplantation experiments using amphibian embryos suggested that the optic vesicle is the source of lens-inducing signals sufficient to generate lens tissues in competent ectoderm (reviewed in Grainger et al., 1996). More recent findings suggest a multistep model for lens induction. There is now good evidence that lens specification occurs at the neurula stage, before the optic vesicle contact the surface ectoderm, and that neural crest cell migration in the frontonasal region is required to restrict the position of the lens placode (Bailey et al., 2006)

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Ectodermal primordium of the lens of the eye. Kimmel et al, 1995.[TAO]

uberon

placoda lentis, lens placodes

(...) an essentially similar sequence of events occurs during the embryonic development of the vertebrate eye. The eye initially develops as a single median evagination of the diencephalon that soon bifurcates to form the paired optic vesicles. As each optic vesicle grows towards the body surface, its proximal part narrows as the optic stalk, and its distal part invaginates to form a two-layered optic cup. (...) The optic cup induces the overlying surface ectoderm first to thicken as a lens placode and then to invaginate and form a lens vesicle that differentiates into the lens.[well established][VHOG]

UBERON:0003073