Fig. 2. Overexpression of Pax3 and Zic1 induces ectopic expression of neural crest markers. Synthetic mRNA was injected into two left animal blastomeres (A-L) or into the ventral animal blastomeres (M-P) at the eight-cell stage. Embryos were harvested at stage 15 and subjected to in situ hybridization with Foxd3 (A,D,G-M,O,P), Slug (B,E,N), Zic1 (C) and Pax3 (F) probes. Pax3 mRNA injection (50 pg/cell; A-C), Zic1 mRNA injection (50 pg/cell; D-F), Pax3-GR mRNA injection (100 pg/cell; G-I), Zic1-GR mRNA injection (100 pg/cell; J-L), and injection of both Pax3 and Zic1 mRNAs (50 pg/cell each; E-H) with lacZ mRNA (200 pg/cell). Dexamethasone (Dex; 10 µM) was added to culture solution at stage 10.5 (H,K) or stage 12 (I,L). Arrows in A,B,H,K,M and N indicate ectopic expression of each marker gene.