Figure 7

wanderer is a nonsense allele of the cortical transcription factor Emx2. (A) The wanderer mutation was mapped to the distal end of chromosome 19 in a region containing the Emx2 gene. Sequencing revealed a T-to-A change (red asterisk) in the first coding exon of Emx2 in wanderer mutants. This mutation (underlined TAT to TAA in chromatogram) is predicted to create an in-frame premature termination codon after 129 residues. (B) The wanderer allele fails to complement a knockout allele of Emx2. A wan/ko trans-heterozygote E18.5 brain displayed both the stereotypically shaped small forebrain and the aberrant TCA fascicles (red arrows) on the ventral surface of the forebrain, seen here with the TCA-TLZ transgene. Open arrowhead indicates normal optic tract. (C-E) DiI or DiA crystals placed in dorsal thalamus of a wild-type E18.5 brain (C) labeled only the optic tract (open arrowhead at optic chiasm) on the ventral surface of the forebrain. However, in an Emx2 homozygous knockout brain (D) or a wanderer homozygous mutant brain (E), the dye labels aberrant TCA fascicles growing on the ventral surface (white arrows), as well as the normal optic tract (open arrowhead). Mutant brain in (D) is slightly tilted back relative to brain in (C).