Figure 3.

Schematic showing the proposed sites of RA (all-trans-retinoic acid; ATRA) function during eye morphogenesis (left) and differentiation (right) [102]. At the early stages of the eye development, the RA generated by RALDH1 and RALDH3 acts as a paracrine signal binding to the RARs located in the perioptic mesenchyme to support the anterior eye segment development and the closure of the optic fissure. Pitx2 is a RA/RAR-regulated transcription factor that is required both for anterior eye segment morphogenesis, as well as the closure of the optic fissure. At the later stages of development, the RA promotes the differentiation of the neural retina. The mechanism is unclear but could involve either a paracrine effect of the RA outside of the neural retina or a direct effect on the cells within the retina itself. https://creativecommons.org/licenses/by/3.0/ (accessed on 3 January 2024).