Fig. 1. Experimental approach. Embryos were injected in both cells at the two-cell stage in the animal pole with 1 ng Smad7 RNA. Ectodermal explants were isolated at stage 9 from both Smad7-injected and uninjected embryos and cultured until stage 15 (neurula). Transcriptional differences were analyzed on a 5000 clone gastrula (stage 10.5) cDNA microarray in duplicate as inverse-dye labeled competitive hybridization (Altmann et al., 2001).