EphB2/B3 gene expression is down-regulated during early embryogenesis in the cadmium-induced omphalocele chick model

In the chick embryo, the administration of cadmium (Cd) induces omphalocele phenotype. The earliest histologic change in this model is observed in the somite 4 hours (H) post treatment, postulating that disruption of somite development in embryogenesis may cause omphalocele phenotype. EphB2 and EphB3 are involved in many embryonic developmental processes, including somitogenesis. EphB2(-/-)EphB3(-/-) double knockouts display omphalocele phenotype. We hypothesized that EphB2/B3 genes are down-regulated in the Cd chick model during the critical period of embryogenesis.

After 60H incubation, chicks were harvested 1H, 4H, and 8H post treatment with saline or Cd and divided into control and Cd groups. Reverse transcriptase-polymerase chain reaction was performed to evaluate gene expression levels of EphB2/B3. Immunofluorescence confocal microscopy was performed to evaluate protein expression/distribution of EphB2/B3.

At 4H post treatment, the messenger RNA expression levels of EphB2/B3 were significantly down-regulated in the Cd group compared with controls (P < .05). The intensity of EphB2/B3 immunofluorescence was markedly diminished at 4H in the Cd-treated embryos, whereas strong immunoreactivity was observed in the somite in controls.

Downregulation of EphB2/B3 during the narrow window of early embryogenesis may interfere with normal somitogenesis, preventing migration of embryonic body wall ventrally and thus causing omphalocele.