title: Altered developmental events in the anterior region of the chick forelimb give rise to avian-specific digit loss.
abstract: BACKGROUND
  Avian forelimb (wing) contains only three digits, and the three-digit formation in the bird forelimb is one of the avian-specific limb characteristics that have been evolutionarily inherited from the common ancestral form in dinosaurs. Despite many studies on digit formation in the chick limb bud, the developmental mechanisms giving rise to the three-digit forelimb in birds have not been completely clarified.
  
  
  RESULTS
  To identify which cell populations of the early limb bud contribute to digit formation in the late limb bud, fate maps of the early fore- and hindlimb buds were prepared. Based on these fate maps, we found that the digit-forming region in the forelimb bud is narrower than that in the hindlimb bud, suggesting that some developmental mechanisms on the anterior-most region lead to a reduced number of digits in the forelimb. We also found temporal differences in the onset of appearance of the ANZ (anterior necrotic zone) as well as differences in the position of the anterior edge of the AER.
  
  
  CONCLUSIONS
  Forelimb-specific events in the anterior limb bud are possible developmental mechanisms that might generate the different cell fates in the fore- and hindlimb buds, regulating the number of digits in birds.
authors.affiliation: Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Sendai, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Nomura
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Yokoyama
authors.forename: Koji
authors.initials: K
authors.lastname: Tamura
mesh_terms: D000818:Animals; D002642:Chick Embryo; D050278:Finger Phalanges / Q000166:cytology / Q000196:embryology*; D018878:Limb Buds / Q000166:cytology / Q000196:embryology*; D014921:Wings, Animal / Q000166:cytology / Q000196:embryology*
keywords: apical ectodermal ridge; apoptosis; bird; fate map; wing