THE MOUSE TYROSINASE PROMOTER IS SUFFICIENT FOR EXPRESSION IN MELANOCYTES AND IN THE PIGMENTED EPITHELIUM OF THE RETINA

The mouse c locus encodes tyrosinase (monophenol monooxygenase; monophenol, L-dopa:oxygen oxidoreductase, EC 1.14.18.1), the key enzyme in melanin synthesis, which is expressed in the pigment epithelium of the retina and in melanocytes derived from the neural crest. To define regulatory regions of the gene that are important for cell type-specific expression, a deletion series of the tyrosinase 5' region was fused to a chloramphenicol acetyltransferase (CAT) reporter gene and electroporated into tyrosinase-expressing and -nonexpressing cell lines. We show that 270 base pairs 5' of the transcriptional start site is sufficient for CAT expression in a human and a mouse melanoma cell line. This 5' flanking fragment, when cloned in the context of a tyrosinase minigene construct and injected into fertilized eggs of an albino mouse strain, is sufficient for cell type-specific expression in mice. The transgenic mice were pigmented in both skin and eyes. In situ hybridization analysis shows that the 270-base-pair regulatory region contains elements sufficient for specific expression of the transgene both in the pigmented epithelial cells of the retina, which are derived from the optic cup, and in neural crest-derived melanocytes.