Fig. 2. Fgf signaling is sufficient for expression of most but not all otic placode markers. (A) Ectoderm from the level of the presumptive trigeminal placode was isolated from 0-4 ss chick embryos and cultured in collagen gels for 24 hours in the presence or absence of Fgf2. A dose response curve for Pax2 expression cultured in Fgf2 for 24 hours is shown. (B) Pax2 is detected in explants after 6 hours of culture in collagen gels, but not at 4 hours. (C) Fgf2 (50 ng/ml) induces expression of Pax2, Dlx3, Epha4 but not Bmp7. None of the four markers are expressed in the absence of Fgf2.