title: Signaling by SHH rescues facial defects following blockade in the brain.
abstract: BACKGROUND
  The Frontonasal Ectodermal Zone (FEZ) is a signaling center in the face that expresses Sonic hedgehog (Shh) and regulates patterned growth of the upper jaw. Blocking SHH in the forebrain blocks Shh expression in the FEZ and creates malformations resembling holoprosencephaly (HPE), while inhibition of BMP signaling in the mesenchyme blocks FEZ formation and causes similar dysmorphology. Thus, the brain could regulate FEZ formation by SHH or BMP signaling, and if so, activating one of these pathways in the face might alleviate the effects of repression of SHH in the brain.
  
  
  RESULTS
  We blocked SHH signaling in the brain while adding SHH or BMP between the neural and facial ectoderm of the frontonasal process. When applied early, SHH restored Shh expression in the FEZ and significantly improved shape outcomes, which contrasts with our previous experiments that showed later SHH treatments have no effect. BMP-soaked beads introduced early and late caused apoptosis that exacerbated malformations. Finally, removal of Smoothened from neural crest cells did not inhibit Shh expression in the FEZ.
  
  
  CONCLUSIONS
  Collectively, this work suggests that a direct, time-sensitive SHH signal from the brain is required for the later induction of Shh in the FEZ. We propose a testable model of FEZ activation and discuss signaling mediators that may regulate these interactions.
authors.affiliation: Department of Orthopaedic Surgery, University of California, San Francisco, San Francisco, California, USA.
authors.forename: H Jonathan
authors.initials: HJ
authors.lastname: Chong
authors.forename: Nathan M
authors.initials: NM
authors.lastname: Young
authors.forename: Diane
authors.initials: D
authors.lastname: Hu
authors.forename: Juhee
authors.initials: J
authors.lastname: Jeong
authors.forename: Andrew P
authors.initials: AP
authors.lastname: McMahon
authors.forename: Benedikt
authors.initials: B
authors.lastname: Hallgrimsson
authors.forename: Ralph S
authors.initials: RS
authors.lastname: Marcucio
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D002642:Chick Embryo; D019465:Craniofacial Abnormalities / Q000378:metabolism*; D053823:Hedgehog Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D015398:Signal Transduction
chemical_list: D053823:Hedgehog Proteins