Conserved regulatory mechanisms of tyrosinase genes in mice and humans.

In vertebrates, melanin production is restricted to pigment cells. This cell type-specific melanogenesis is considered to involve cell type-specific expression of the tyrosinase gene. Recently, there have been several reports that sequences in the 5' flanking region of the mouse tyrosinase gene are responsible for cell type-specific expression of the transgene in mice. As the first step in the study of the evolution of the regulatory mechanisms for tyrosinase gene function in vertebrates, we constructed a fused gene, hg-Tyrs-J, which includes a 1.0-kb 5' flanking sequence of the human tyrosinase gene fused with mouse tyrosinase cDNA. By introducing the fused gene into fertilized eggs of albino mice, we obtained two mice that exhibited pigmentation in the skin and eyes and established a transgenic line from one of them. Further analyses revealed that the transgene was expressed cell type-specifically in these transgenic mice. We conclude, therefore, that the 1.0 kb 5' upstream region of the human tyrosinase gene contains conserved cis-elements essential for cell type-specific expression of the tyrosinase genes in mice and humans. Results of our study may provide a clue to elucidate the evolutionary process of regulatory mechanisms of the tyrosinase gene.