title: Frame-shifts of digit identity in bird evolution and Cyclopamine-treated wings.
abstract: A highly conserved spatio-temporal pattern of cartilage formation reveals that the digits of the bird wing develop from positions that become digits 2, 3, and 4 in other amniotes. However, the morphology of the digits of early birds like Archaeopteryx corresponds to that of digits 1, 2, and 3 of other archosaurs. A hypothesis is that a homeotic "frame-shift" occurred, such that in the bird wing, digits 1, 2, and 3 develop from the embryological positions of digits 2, 3, and 4. Experimental homeotic transformations of single digits are well-documented, but frame-shifts of more than one digit are not. We investigated the pattern of cartilage formation in the development of Cyclopamine-treated wings. When Cyclopamine was applied between stages 18 and 21, morphologies that normally develop from positions 2 and 3 developed from positions 3 and 4. The serial shift of digit identity toward posterior confirms a mechanistic possibility that was previously inferred from the evolutionary history of birds.
authors.affiliation: Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT 06520-8106, USA.
authors.forename: Alexander O
authors.initials: AO
authors.lastname: Vargas
authors.forename: Günter P
authors.initials: GP
authors.lastname: Wagner
mesh_terms: D000489:Alligators and Crocodiles; D000818:Animals; D001717:Birds / Q000235:genetics* / Q000502:physiology*; D019521:Body Patterning / Q000235:genetics; D002356:Cartilage / Q000378:metabolism / Q000502:physiology; D019143:Evolution, Molecular; D016368:Frameshift Mutation; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics; D051379:Mice; D010641:Phenotype; D013997:Time Factors; D014704:Veratrum Alkaloids / Q000494:pharmacology*; D014921:Wings, Animal / Q000033:anatomy & histology* / Q000502:physiology
chemical_list: D018398:Homeodomain Proteins; D014704:Veratrum Alkaloids; C000541:cyclopamine