Fig. 4.

The EGFR pathway induces wntD expression and limits the dorsoventral concentration gradient of nuclear Dorsal. (A-C) Stage 6 wild-type (A) and mutant DSor (B) and Egfr (C) embryos were hybridized using a digoxigenin-labeled wntD RNA probe. RTK signaling is impeded in DSor (B) and Egfr (C) mutants, and the expression of wntD is blocked. The weak ventral wntD expression in the mutant embryos (B,C) probably results from ineffective induction by Dl alone. Arrows point to the domain of wntD expression. (D-F) Representative cross-section images of stage 6 wild-type (D), wntD (E) and rho vn (F) embryos, stained for Dl (red). (A-C) Embryos are oriented with anterior to the left and dorsal side upwards. (G,H) Quantification of nuclear Dl gradients along the DV axis in wild-type and mutant embryos. Data are the average gradients±s.e.m. Ventral levels of nuclear Dl are significantly higher in wntD (G; red; n=40 measurements) and rho vn mutants (H; red; n=28 measurements), relative to wild-type controls (blue; n=36 and 42 measurements, respectively), suggesting that EGFR-induced WntD antagonizes nuclear accumulation of Dl along the DV axis. For the nuclear Dl gradient, two values were extracted from each embryo (see Materials and methods).