The gene was disrupted by replacement of exon 1 and flanking sequences with a PGK-Hprt cassette via homologous recombination. The gene targeting event results in deletion of a splice acceptor site necessary for processing different protein isoforms, a 16 amino acid signal sequence, and 18 amino acids of the mature protein. Northern blot analysis of various tissues from homozygous mutant animals using a 620 bp cDNA probe did not detect gene expression. (J:47610)