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 high level of gene transcript in whole brain, cortex, subcortical region, brainstem, olfactory bulb, spinal cord, eye, spleen and testis and low levels in cerebellum, thymus, skin, urinary bladder, pituitary gland, epididymis, coagulating gland, prostate gland, and white fat. However, beta-galactosidase expression from this allele is faintly detectable in only in a few follicles in the ovary.