title: Embryological evidence identifies wing digits in birds as digits 1, 2, and 3.
abstract: The identities of the digits of the avian forelimb are disputed. Whereas paleontological findings support the position that the digits correspond to digits one, two, and three, embryological evidence points to digit two, three, and four identities. By using transplantation and cell-labeling experiments, we found that the posteriormost digit in the wing does not correspond to digit four in the hindlimb; its progenitor segregates early from the zone of polarizing activity, placing it in the domain of digit three specification. We suggest that an avian-specific shift uncouples the digit anlagen from the molecular mechanisms that pattern them, resulting in the imposition of digit one, two, and three identities on the second, third, and fourth anlagens.
authors.affiliation: Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai 980-8578, Japan. tam@m.tohoku.ac.jp
authors.forename: Koji
authors.initials: K
authors.lastname: Tamura
authors.forename: Naoki
authors.initials: N
authors.lastname: Nomura
authors.forename: Ryohei
authors.initials: R
authors.lastname: Seki
authors.forename: Sayuri
authors.initials: S
authors.lastname: Yonei-Tamura
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Yokoyama
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002642:Chick Embryo / Q000196:embryology*; D003370:Coturnix / Q000196:embryology*; D005552:Forelimb / Q000196:embryology / Q000637:transplantation; D053823:Hedgehog Proteins / Q000378:metabolism; D006614:Hindlimb / Q000196:embryology / Q000637:transplantation; D018878:Limb Buds / Q000196:embryology; D051379:Mice; D015398:Signal Transduction; D014034:Toes / Q000196:embryology; D014921:Wings, Animal / Q000196:embryology*
chemical_list: D053823:Hedgehog Proteins