Neural Tube DefectsNeural TubeNeurulationGene Expression Regulation, DevelopmentalNeural CrestSpinal DysraphismAnencephalyNeural PlateNervous SystemBody PatterningEmbryo, MammalianCentral Nervous SystemNotochordMorphogenesisCell PolarityChick EmbryoEmbryo LossPaired Box Transcription FactorsEmbryonic DevelopmentEctodermIn Situ HybridizationXenopus ProteinsTeratogensRhombencephalonFolic AcidEmbryonic and Fetal DevelopmentPregnancyMice, Mutant Strains