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, eye, pancreas, kidneys, trachea, larynx, esophagus, pituitary gland, parathyroid gland, tongue, skin, male and female reproductive systems.