Fig. 7. Upregulation of pre-placodal markers correlates with Fgf responsiveness. (A) Anterior epiblast was isolated from HH stage 3⁺-4 quail embryos and grafted into chick hosts at 0-4 ss. Grafts were placed either adjacent to the neural plate at the level of the presumptive trigeminal placode, or lateral to the presumptive trigeminal placode. Grafts were removed after 2 or 8 hours and cultured for a further 12 hours in the presence or absence of 50 ng/ml Fgf2. Control pieces of epiblast were isolated and cultured in Fgf2 for 20 hours without first being grafted into chick hosts. (B) Pax2 expression in cultured explants of transplanted quail epiblast, detected by QCPN expression. Pax2 is induced only by Fgf2 in explants grafted into the pre-placodal region for 8 hours. Two representative explants are shown for this condition, separated by broken lines. (C) Epiblast does not express Eya2 or label with pan-Dll antibodies after 20 hours of culture in the presence or absence of Fgf2.