title: Disturbance of SHH signalling pathway during early embryogenesis in the cadmium-induced omphalocele chick model.
abstract: BACKGROUND
  Administration of cadmium (Cd) after 60 h (H) incubation induces ventral body wall defect (VBWD) similar to the omphalocele phenotype in the chick embryo. In this model, the earliest histological changes have been observed in somites commencing at 4-h post-treatment (4H). The molecular mechanism by which Cd acts in this critical period of embryogenesis still remains unclear. Sonic hedgehog (SHH) signalling plays an important role in vertebrate development, including somitogenesis and thus ventral body wall formation. Patched (PTCH), a cell membrane receptor for SHH, is expressed in somites and Patched knockout mice display somite dysfunction. Another transmembrane receptor, Smoothened (SMO), is also expressed in somites and transduces the SHH signal regulated by PTCH. We designed this study to test the hypothesis that SHH signalling is downregulated during the critical period of early embryogenesis in the Cd-induced omphalocele chick model.
  
  
  METHODS
  After 60 h of incubation, chicks were exposed to either chick saline or 50 μL of 50 μM cadmium acetate and divided into two groups: control and Cd (n = 24 for each group). Chicks were harvested 1, 4, and 8 h post-treatment. Real-time RT-PCR was performed to evaluate the relative mRNA expression level of SHH, PTCH and SMO. Immunofluorescence confocal microscopy was then performed to evaluate protein expression/distribution of SHH, PTCH and SMO.
  
  
  RESULTS
  The relative mRNA expression levels of SHH, PTCH and SMO were significantly downregulated in the Cd group compared to controls at 4H post treatment, whereas, there were no significant differences at the other time points. Immunohistochemistry revealed that the intensity of SHH, PTCH and SMO was markedly diminished at 4 h in Cd-treated embryos compared to controls.
  
  
  CONCLUSIONS
  Disturbance of the SHH signalling pathway as evidenced by SHH, PTCH and SMO downregulation during the narrow window of early embryogenesis may result in somite maldevelopment, contributing to the omphalocele phenotype in the Cd chick model.
authors.affiliation: The National Children's Research Centre, Our Lady's Children Hospital, Dublin 12, Ireland.
authors.forename: Naho
authors.initials: N
authors.lastname: Fujiwara
authors.forename: Johannes
authors.initials: J
authors.lastname: Duess
authors.forename: Prem
authors.initials: P
authors.lastname: Puri
authors.forename: Jennifer
authors.initials: J
authors.lastname: Thompson
mesh_terms: D000818:Animals; D002104:Cadmium; D002642:Chick Embryo; D004195:Disease Models, Animal; D015536:Down-Regulation / Q000235:genetics; D047108:Embryonic Development / Q000235:genetics*; D053823:Hedgehog Proteins / Q000235:genetics*; D006554:Hernia, Umbilical / Q000196:embryology* / Q000235:genetics*; D018613:Microscopy, Confocal; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015398:Signal Transduction / Q000235:genetics
chemical_list: D053823:Hedgehog Proteins; D002104:Cadmium