title: Is retinoic acid genetic machinery a chordate innovation?
abstract: Development of many chordate features depends on retinoic acid (RA). Because the action of RA during development seems to be restricted to chordates, it had been previously proposed that the "invention" of RA genetic machinery, including RA-binding nuclear hormone receptors (Rars), and the RA-synthesizing and RA-degrading enzymes Aldh1a (Raldh) and Cyp26, respectively, was an important step for the origin of developmental mechanisms leading to the chordate body plan. We tested this hypothesis by conducting an exhaustive survey of the RA machinery in genomic databases for twelve deuterostomes. We reconstructed the evolution of these genes in deuterostomes and showed for the first time that RA genetic machinery--that is Aldh1a, Cyp26, and Rar orthologs--is present in nonchordate deuterostomes. This finding implies that RA genetic machinery was already present during early deuterostome evolution, and therefore, is not a chordate innovation. This new evolutionary viewpoint argues against the hypothesis that the acquisition of gene families underlying RA metabolism and signaling was a key event for the origin of chordates. We propose a new hypothesis in which lineage-specific duplication and loss of RA machinery genes could be related to the morphological radiation of deuterostomes.
authors.affiliation: Institute of Neuroscience, University of Oregon, Eugene, OR 97403, USA.
authors.forename: Cristian
authors.initials: C
authors.lastname: Cañestro
authors.forename: John H
authors.initials: JH
authors.lastname: Postlethwait
authors.forename: Roser
authors.initials: R
authors.lastname: Gonzàlez-Duarte
authors.forename: Ricard
authors.initials: R
authors.lastname: Albalat
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D002816:Chordata, Nonvertebrate / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D004447:Echinodermata / Q000235:genetics / Q000378:metabolism; D005057:Eukaryotic Cells / Q000378:metabolism; D019143:Evolution, Molecular; D016678:Genome; D010802:Phylogeny; D018168:Receptors, Retinoic Acid / Q000235:genetics; D000072516:Retinoic Acid 4-Hydroxylase; D016415:Sequence Alignment; D015398:Signal Transduction; D014212:Tretinoin / Q000378:metabolism*; D014714:Vertebrates / Q000145:classification / Q000235:genetics* / Q000378:metabolism
chemical_list: D018168:Receptors, Retinoic Acid; D014212:Tretinoin; D003577:Cytochrome P-450 Enzyme System; D000072516:Retinoic Acid 4-Hydroxylase; D000445:Aldehyde Oxidoreductases