Expression of opsin molecule in cultured murine melanocyte.

Recently, we demonstrated the expression of rhodopsin in the tail fin of the Xenopus tadpole, in which photosensitive melanophores exist (Miyashita et al, The photoreceptor molecules in Xenopus tadpole tail fin, in which melanophores exist. Zool Sci 18:671-674, 2001). The presence of opsin molecules in pigment cells of lower vertebrates raises the possibility that pigment cells in animal skin function as photosensors generally. To explore this possibility in higher vertebrates, we tried to detect photoreception molecules in mammalian melanocytes. We extracted total RNA from Melan a2, a cell line of immortal murine melanocyte, which is derived from C57BL mice. The DNA sequence obtained by reverse transcriptase-polymerase chain reaction (RT-PCR) amplification was homologous to the corresponding portion of the sequence of ocular rhodopsin of mice. Western blotting and fluorescent immunocytochemistry showed the existence of the opsin protein in the melanocytes. Another cell line, EL4, which is derived from lymphoma of C57BL/6N, scarcely expresses opsin mRNA, as judged by RT-PCR. Thus expression of the opsin gene is not ubiquitous among immortal cell lines. Detection of rhodopsin mRNA in murine tissues of C57BL/6N by RT-PCR showed its presence in the eye and skin but not in the liver. The role of the opsin molecule in melanocyte is not known at present, but this will provide additional insight into photoreception systems in animal skin.