Vertebrate Eye Development at Different Stages

The vertebrate eye originates from the frontal neural plate, the ectoderm of the head surface and mesenchyme drawn from the neural crest. There is a need for proper synchronization of ocular tissues to guarantee the formation of a functional eye. The frontal neural plate gives rise to the single central eye field by dividing to form the optic vesicle that evaginates in the direction of the head surface ectoderm. Consequently, the optic vessel and surface ectoderm invaginate yielding the double-layered optic cup and lens vesicle, correspondingly.

The WNT/β-catenin signalling pathway plays a role in regulating this process, particularly during the initial phases of lens formation and retinal pigment epithelium (RPE) development. TGFβ is secreted by the periocular mesenchyme. This molecule transmits its signal to the surface ectoderm and induces WNT2b, which triggers WNT/β-catenin signalling to quell the fate of the lens by inhibiting the expression of Pax6.

However, Pax6 prevents WNT/β-catenin in the lens placode, which commences lens formation. Meanwhile, the surface ectoderm produces WNTs to initiate the WNT/β-catenin pathway in the RPE, which stimulates the expression of two other molecules Otx2 and Mitf. The three (Otx2, Pax6 and Mitf) then work in synchrony to regulate the production of RPE as shown below.

Vertebrate eye development at different stages: early optic vesicle stage (A), optic vesicle stage (B), optic cup stage (C) and closing of the lens vesicle (D). E and F show the interaction of the WNT/β-catenin signalling during eye development.