Differential perturbation of the Fgf/Erk1/2 and Shh pathways in the C57BL/6N and SWV embryonic limb buds after mid-gestational cadmium chloride administration

Abstract

The differential susceptibility of inbred mouse strains to teratogen-induced malformations can serve as a model to assess the molecular pathogenesis of dysmorphology. Using such a model, the teratogenic effect of cadmium chloride (CdCl 2), which results in limb reduction deformities in the C57BL/6N mouse strain, but not in the SWV strain, was found to correlate with reduction of the expression domains of Fgf8/4 (fibroblast growth factor-8 and -4) in the apical ectodermal ridge (AER) and Shh (sonic hedgehog) in the posterior mesenchyme, as well as reduction of MAPK/Erk1/2 (the mitogen-activated protein kinase/extracellular regulated kinase 1/2) phosphorylation (pErk1/2) in the mesenchyme throughout the limb bud. The pattern of pErk1/2 reduction did not consistently reflect the pattern of Fgf8/4 reduction suggesting that CdCl 2 might affect pErk1/2 through an Fgf-independent pathway. Other potential downstream mediators of the Fgf pathway including Mkp3 and Fgf10 as well as pMek (phosphorylated MAPK/Erk1/2 kinase) were not different in limb buds between the two strains at the studied time points. The effect of CdCl 2 on skeletogenesis was traced in time to the early stages of pre-chondrogenic condensation as determined by the Sox9 expression domain. The data of the present study indicate that a differential strain response to CdCl 2-induced forelimb digital loss may be due to a polymorphic interference with the Fgf/Shh positive feedback loop and Erk1/2 phosphorylation.