One‐cell stage embryos were injected animally with mRNAs encoding the bmp4 (50 pg) and/or FGF dominant‐negative receptor (FGF‐DNR, 1.5 ng) proteins. AC explants were removed from control and injected embryos at blastula stage 9, and explants were cultured to neurula stage 16. Total RNA was isolated from five control embryos (lane 2), and from eighteen ACs from each group (lanes 3–6). In addition to fgf3, neural, epidermal, and mesodermal markers were examined by sqRT–PCR: hindbrain (krox20, hoxb3), spinal cord (hoxb9, hoxc10, cdx4), lateral mesoderm (osr1), dorsal–lateral mesoderm muscle actin (MA), and epidermal cytokeratin (E13). ODC is the control for quantitating RNA levels. ‐RT–PCR was performed on total RNA isolated from control embryos (lane 1).