A bacterial lacZ gene was inserted into the gene such that the endogenous gene promoter drives expression of beta-galactosidase. While RT-PCR analysis detects a gene transcript in most tissues analyzed, highest levels are seen in skin, gallbladder, skeletal muscle, tongue and ovary and no transcripts are detectable in bone marrow and cecum. Beta-galactosidase expression from this allele is detectable in brain, sciatic nerve, eyes, heart, larynx, skeletal muscle, testis and connective tissue.