Exon 1 was disrupted by insertion of a PGK-neo cassette by homologous recombination. RNase protection assays using probes to exon 1 and exon 3 did not detect gene expression in brain of homozygous mutant animals. Western blot analysis and immunohistochemistry of brain sections from homozygous mutant animals confirmed the absence of protein expression. (J:47438)