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 brain, spinal cord, pancreas, lymph nodes, skin, urinary bladder, pituitary gland, adrenal gland, small intestine and prostate gland and at lower levels in olfactory bulb, lung, liver, kidney, spleen, bone marrow, gallbladder, stomach, colon, testis, seminal vesicle, coagulating gland, ovary, uterus and white fat; beta-galactosidase expression is detectable in urinary bladder and a few cells in the muscularis, but not in brain, spinal cord, sciatic nerve, eyes, thymus, spleen, lymph nodes, bone marrow, aorta, heart, lung, liver, pancreas, kidney, thyroid gland, pituitary gland, adrenal glands, skeletal muscle, skin, testis, prostate gland, ovary, uterus and cervix.