Fig. 3.

Blocking fibroblast growth factor (FGF) signaling prevents cells from delaminating and contributing to the mesenchyme. Transverse section through the ophthalmic trigeminal (opV) placode region of a 15 somite stage (ss) embryo cultured for 18 hr to approximately the 27 ss. Embryo head was cultured in either dimethyl sulfoxide (DMSO) or SU5402, immunostained for Pax3 (red; A, C) and Islet1 (green; B, D). A,C: In SU5402-cultured embryo heads, significantly fewer Pax3+ cells delaminate and migrate into the mesenchyme, whereas in DMSO-cultured embryos the cells continue to delaminate normally and move into the mesenchyme. B,D: Placode cells in SU5402 did not increase neuronal differentiation as shown by the scarce Islet-1 expression in the ectoderm. E: Histogram showing Pax3+ mesenchyme cells in DMSO (n = 7) or SU5402 (n = 9) embryos. Error bars depict SEM. The reduction in the number of Pax3+ cells in the mesenchyme of experimental embryos compared with controls is statistically significant (P < 0.01).