Visualization of the melanosome transfer-inhibition in a mouse epidermal cell co-culture model.

Transfer of melanin-containing melanosomes from melanocytes to neighboring keratinocytes results in skin pigmentation. To provide a more practical method of visualizing melanosomes in melanocytes as well as in keratinocytes, we attempted to use murine cell lines instead of human primary cells. We generated various fluorescent fusion proteins of tyrosinase, a melanin synthesis enzyme located in the melanosome, by using green fluorescent protein and red fluorescent protein. The intracellular localization of tyrosinase was then examined by fluorescence and confocal microscopy. Co-culture of murine melanocytes and keratinocytes was optimized and melanosome transfer was either stimulated with alphaMSH or partially inhibited by niacinamide. To the best of our knowledge, this is the first study showing that a murine co-culture model, in addition to human primary cell co-culture, can be a good tool for depigmenting agent screening by monitoring melanosome transfer.