title: Full regeneration of the tribasal Polypterus fin.
abstract: Full limb regeneration is a property that seems to be restricted to urodele amphibians. Here we found that Polypterus, the most basal living ray-finned fish, regenerates its pectoral lobed fins with a remarkable accuracy. Pectoral Polypterus fins are complex, formed by a well-organized endoskeleton to which the exoskeleton rays are connected. Regeneration initiates with the formation of a blastema similar to that observed in regenerating amphibian limbs. Retinoic acid induces dose-dependent phenotypes ranging from inhibition of regeneration to apparent anterior-posterior duplications. As in all developing tetrapod limbs and regenerating amphibian blastema, Sonic hedgehog is expressed in the posterior mesenchyme during fin regeneration. Hedgehog signaling plays a role in the regeneration and patterning processes: an increase or reduction of fin bony elements results when this signaling is activated or disrupted, respectively. The tail fin also regenerates but, in contrast with pectoral fins, regeneration can resume after release from the arrest caused by hedgehog inhibition. A comparative analysis of fin phenotypes obtained after retinoic acid treatment or altering the hedgehog signaling levels during regeneration allowed us to assign a limb tetrapod equivalent segment to Polypterus fin skeletal structures, thus providing clues to the origin of the autopod. We propose that appendage regeneration was a common property of vertebrates during the fin to limb transition.
authors.affiliation: Department of Developmental Genetics and Molecular Physiology, Instituto de Biotecnología,  Universidad Nacional Autónoma de México, Cuernavaca, Morelos, 62210,  Mexico.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Cuervo
authors.forename: Rocío
authors.initials: R
authors.lastname: Hernández-Martínez
authors.forename: Jesús
authors.initials: J
authors.lastname: Chimal-Monroy
authors.forename: Horacio
authors.initials: H
authors.lastname: Merchant-Larios
authors.forename: Luis
authors.initials: L
authors.lastname: Covarrubias
mesh_terms: D000818:Animals; D005075:Biological Evolution; D019521:Body Patterning; D001842:Bone and Bones / Q000378:metabolism; D005121:Extremities / Q000502:physiology*; D005399:Fishes; D053823:Hedgehog Proteins / Q000378:metabolism; D017403:In Situ Hybridization; D008954:Models, Biological; D008969:Molecular Sequence Data; D010641:Phenotype; D012038:Regeneration / Q000502:physiology*; D015398:Signal Transduction; D014212:Tretinoin / Q000737:chemistry / Q000378:metabolism; D014704:Veratrum Alkaloids / Q000378:metabolism
chemical_list: D053823:Hedgehog Proteins; D014704:Veratrum Alkaloids; D014212:Tretinoin; C000541:cyclopamine