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Fig. 10. RA-dependent eye morphogenesis is orchestrated by the NCC-derived periocular mesenchyme. RALDH1 (red) and RALDH3 (orange), expressed in the retina, the retinal-pigmented epithelium, the lens and the corneal ectoderm, are the only RA-synthesizing enzymes required in the eye region from E10.5 onwards. The RA synthesized in these locations (yellow arrows) diffuses towards the periocular mesenchyme (POM, blue), where it determines eye morphogenesis through the activation of RXR{alpha}/RARß and RXR{alpha}/RAR{gamma} heterodimers. The latter may control (1) the Eya2-dependent apoptosis involved in POM remodeling; (2) the expression of Foxc1 and Pitx2 transcription factors that are required for the eye anterior segment morphogenesis; and (3) the production of an unknown signal (question mark) necessary for the growth of the ventral retina. Asterisk indicates the RA-depleted zone expressing the catabolizing enzymes CYP26A1 and CYP26C1. This drawing is representative of the E11.5 condition.