A floxed pgk-neo cassette was inserted in intron 2 and a Cys98stop nonsense mutation was inserted in exon 2 via homologous recombination. The floxed neo cassette was then removed by Cre mediated recombination. Immunohistochemical analysis detected expression of a mutant protein in the supraoptic nucleus, the suprachiasmatic nuclei, and the paraventricular nucleus in homozygous and heterozygous mice. This analysis also confirmed the absence of wild-type protein expression in homozygous mice. (J:147993)