Enhancer Elements, Genetic; Homeodomain Proteins/genetics; Prosencephalon/embryology; Prosencephalon/metabolism; Transcription Factors/genetics; Animals; Base Sequence; Binding Sites/genetics; Cerebral Cortex/embryology; Cerebral Cortex/metabolism; Conserved Sequence; DNA/genetics; DNA/metabolism; DNA Primers/genetics; Female; Gene Expression Regulation, Developmental; Gestational Age; Mice; Mice, Knockout; Mice, Mutant Strains; Mice, Transgenic; Molecular Sequence Data; Mutation; Otx Transcription Factors/metabolism; Phenotype; Pregnancy; Sequence Homology, Nucleic Acid; Smad Proteins/metabolism; Species Specificity; TCF Transcription Factors/metabolism; Telencephalon/embryology; Telencephalon/metabolism; Transcription Factors/deficiency; Xenopus/genetics