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, spleen, thymus, lymph nodes and urinary bladder; beta-galactosidase expression is detectable in brain and testis, but not in the spinal cord, spleen, thymus, lymph nodes or urinary bladder.