Retinoic acid and development of the retina

Abstract

Abstract Retinoic acid (RA) is known as the activating trigger for a large number of processes in developing and mature vertebrates, and it plays a pivotal role in eye development. We present here a brief review of the RA system in general, and we summarize the evidence for a determining role of RA in the embryonic eye. The earliest and most significant ocular feature influenced by RA is the dorso-ventral axis. A lasting differential expression of different RA generating enzymes along the retinal dorso-ventral axis then creates very high endogenous RA levels, as well as a ventro-dorsal RA gradient, features that are likely to direct morphogenesis along this axis in the embryonic eye. RA is also likely to play a significant role in the function of the mature eye, as some of the chromophore released from photo-bleached rhodopsin is converted to RA, a mechanism for light to directly influence gene expression. The pivotal role of RA in eye morphogenesis may represent a developmental correlate of an evolutionary origin of RA-mediated transcriptional regulation from retinoid usage in vision.