Body PatterningHedgehog ProteinsEmbryonic InductionGastrulaNotochordEmbryo, NonmammalianMorphogenesisDrosophila ProteinsGene Expression Regulation, DevelopmentalDrosophilaEctodermBone Morphogenetic ProteinsMesodermZebrafish ProteinsGenes, InsectXenopus ProteinsHomeodomain ProteinsTranscription FactorsZebrafishTrans-ActivatorsSignal TransductionIn Situ HybridizationRepressor ProteinsDNA-Binding ProteinsChick EmbryoProteinsMutation