Human skin pigmentation is caused by the synthesis of melanin and by its distribution in skin and in hair follicles. The melanogenesis process is initiated within melanocytes, and more particularly in melanosomes, which are lysosome-related membrane-bound organelles. Melanogenesis starts by the production of non-pigmented pre-melanosomes, which are mostly composed of fibers (Pmel 17 protein). Enzymes (tyrosinase, Tyrp1, DCT) are then transferred to melanosomes for the biotransformation of tyrosine into melanin.
Mature melanin-containing melanosomes are transported via a microtubule network to the melanocyte dendritic extremities. In order to transfer the melanosomes to the keratinocyte cytoplasm, melanocytes project their dendrites into the neighboring keratinocytes, at an approximate ratio of one melanocyte to thirty five keratinocytes (one pigmentary unit). Melanosome transfer is a key step of the skin pigmentation process.
The purpose of this assay is, by using flow cytometry, to evaluate the capacity of compounds (molecules, active ingredients, extracts, etc.) to inhibit the melasome transfer in a co-culture model of normal human melanocytes and keratinocytes.