title: Signals from the brain induce variation in avian facial shape.
abstract: BACKGROUND
  How developmental mechanisms generate the phenotypic variation that is the raw material for evolution is largely unknown. Here, we explore whether variation in a conserved signaling axis between the brain and face contributes to differences in morphogenesis of the avian upper jaw. In amniotes, including both mice and avians, signals from the brain establish a signaling center in the ectoderm (the Frontonasal ectodermal zone or "FEZ") that directs outgrowth of the facial primordia.
  
  
  RESULTS
  Here we show that the spatial organization of this signaling center differs among avians, and these correspond to Sonic hedgehog (Shh) expression in the basal forebrain and embryonic facial shape. In ducks this basal forebrain domain is present almost the entire width, while in chickens it is restricted to the midline. When the duck forebrain is unilaterally transplanted into stage matched chicken embryos the face on the treated side resembles that of the donor.
  
  
  CONCLUSIONS
  Combined with previous findings, these results demonstrate that variation in a highly conserved developmental pathway has the potential to contribute to evolutionary differences in avian upper jaw morphology. Developmental Dynamics 244:1133-1143, 2015. © 2015 Wiley Periodicals, Inc.
authors.affiliation: Department of Orthopaedic Surgery, San Francisco General Hospital, Orthopaedic Trauma Institute, The University of California at San Francisco, School of Medicine, San Francisco, California.
authors.forename: Diane
authors.initials: D
authors.lastname: Hu
authors.affiliation: Department of Orthopaedic Surgery, San Francisco General Hospital, Orthopaedic Trauma Institute, The University of California at San Francisco, School of Medicine, San Francisco, California.
authors.forename: Nathan M
authors.initials: NM
authors.lastname: Young
authors.affiliation: Department of Mathematics, Florida State University, Tallahassee, Florida.
authors.forename: Qiuping
authors.initials: Q
authors.lastname: Xu
authors.affiliation: Department of Cell Biology and Anatomy, Alberta Children's Research Institute for Child and Maternal Health and the McCaig Bone and Joint Institute, University of Calgary, Calgary, Canada.
authors.forename: Heather
authors.initials: H
authors.lastname: Jamniczky
authors.affiliation: Department of Cell Biology and Anatomy, Alberta Children's Research Institute for Child and Maternal Health and the McCaig Bone and Joint Institute, University of Calgary, Calgary, Canada.
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Green
authors.affiliation: Department of Mathematics, Florida State University, Tallahassee, Florida.
authors.forename: Washington
authors.initials: W
authors.lastname: Mio
authors.affiliation: Department of Orthopaedic Surgery, San Francisco General Hospital, Orthopaedic Trauma Institute, The University of California at San Francisco, School of Medicine, San Francisco, California.
authors.forename: Ralph S
authors.initials: RS
authors.lastname: Marcucio
authors.affiliation: Department of Cell Biology and Anatomy, Alberta Children's Research Institute for Child and Maternal Health and the McCaig Bone and Joint Institute, University of Calgary, Calgary, Canada.
authors.forename: Benedikt
authors.initials: B
authors.lastname: Hallgrimsson
keywords: Sonic hedgehog (Shh); craniofacial development; forebrain; frontonasal ectodermal zone (FEZ); variation