A bacterial lacZ gene was inserted into the gene such that the endogenous gene promoter drives expression of beta-galactosidase. RT-PCR analysis detects a gene transcript in all tissues examined; beta-galactosidase expression is detectable in brain, spinal cord, eyes, liver, pancreas, kidney, urinary bladder, parathyroid gland, trachea, pituitary gland, adrenal glands, skeletal muscle, skin, testis, prostate gland and cervix.