Methods: We used PD98059, an ERK inhibitor, to inhibit the ERK signaling in facial region. We implanted PD98059-soaked bead into the first branchial arch of chick embryo at the early stage of facial development. After the proper incubation and the skeletal staining, the skeletal morphology was microscopically analyzed. To elucidate the detailed underlying mechanism for its morphologic change, we searched the change of cell differentiation and condensation. In addition, the pattern of cell migration with DiI (dioctadecyl tetramethylindocarbocyanine perchlorate) and the change of gene expression by in situ hybridization were made.
Results: The inhibition of ERK signaling with PD98059 caused the various morphologic changes. The inhibition of ERK signaling resulted in the deviation of upper beak toward the treated side and the shortening of lower beak with abnormal cartilage formation. And we analyzed the relationship between malformation and cell migration, the change of cell condensation. As a result, there is no change of cell migration. But cell condensation was increased in mandibular prominence. We also confirm that inhibition of ERK signaling caused the change of expression pattern of Fgf8 in nasal fit.
Conclusion: All the results demonstrated that ERK signaling is involved in the regulation of chondrogenic cell differentiation and skeletal facial patterning.