Retinoic acid (RA)-signaling pathway. Extracellular binding and import of retinol, retinol conversion, oxidation of retinaldehyde to ATRA and/or 9-cis-RA, binding to RA receptors (RAR, RXR), degradation of RA to metabolites, and activation/repression of retinoic acid response elements (RARE). This diagram shows the activation (Arrow) of a target gene (Red box). Lightning bolts indicate genes with associated human eye development diseases. Abbreviations: RBP4, retinol-binding protein 4; STRA6, stimulated by retinoic acid 6; RDH5, retinol dehydrogenase 5; RDH10, retinol dehydrogenase 10; ADH1, alcohol dehydrogenase 1; ADH7, alcohol dehydrogenase 7; CRBP, cellular retinol-binding protein; ALDH1A1, aldehyde dehydrogenase 1 family member A1; ALDH1A2, aldehyde dehydrogenase 1 family member A2; ALDH1A3, aldehyde dehydrogenase 1 family member A3; CYP26A1, cytochrome P450 family 26 subfamily A member 1; CYP26B1, cytochrome P450 family 26 subfamily B member 1; CYP26C1, cytochrome P450 family 26 subfamily C member 1; ATRA, all-trans-retinoic acid ; 9-cis-RA; RAR, retinoic acid receptor ; RXR, Retinoic X Receptor; RARE, retinoic acid response elements.