Authors: Takashi Doi Prem Puri John Bannigan Jennifer Thompson
Publish Date: 2010/07/13
Volume: 26, Issue: 10, Pages: 1017-1023
Abstract
In the chick embryo administration of cadmium Cd induces omphalocele phenotype HoxB2 and HoxB4 expressed in cell types that contribute to ventral body wall VBW formation act together to mediate proper closure of the VBW involving a key downstream transcription factor Alx4 HoxB2 and HoxB4 knockout mice display VBW defects with specific downregulation of Alx4 gene expression while homozygous Alx4 knockouts show omphalocele phenotype Although the earliest histological changes in the Cd chick model occur commencing at 4H post treatment the exact timing and molecular mechanism by which Cd acts is still unclear We hypothesized that HoxB2 HoxB4 and Alx4 genes are downregulated during the critical timing of very early embryogenesis in the Cdinduced omphalocele chick modelAfter 60H incubation chick embryos were harvested at 1H 4H and 8H after treatment with saline or Cd and divided into controls and Cd group n = 24 for each group RT–PCR was performed to investigate the gene expression of HoxB2 HoxB4 and Alx4 and statistically analyzed significance was accepted at p 005 Immunohistochemical staining was also performed to evaluate the protein expression/distribution of HoxB2 HoxB4 and Alx4 in the chick embryoThe expression levels of HoxB2 HoxB4 and Alx4 gene at 4H were significantly downregulated in the Cd group as compared to controls whereas there were no significant differences at the other time points Immunoreactivity of HoxB2 HoxB4 and Alx4 at 4H is also markedly decreased in the ectoderm and the dermomyotome in the Cd chick model as compared to controlsDownregulation of HoxB2 HoxB4 and Alx4 expression during the narrow window of early embryogenesis may cause omphalocele in the Cd chick model by interfering with molecular signaling required for proper VBW formation Furthermore these results support the concept that HoxB2 HoxB4 and Alx4 genes work together to mediate proper VBW formation
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