Melanocytes

Melanocytes are pigment-producing cells derived from neural crest cells. In humans they reside primarily in the epidermis, especially the basal layer of the epidermis, and in hair follicle bulbs. They are also found in the uveal tract of the eye and other pigmented tissues.

Melanocytes synthesize melanin within specialized organelles called melanosomes. The pigment exists mainly as eumelanin (brown/black) and pheomelanin (red-yellow). The enzyme tyrosinase initiates melanin biosynthesis, with other enzymes like TYRP1 and DCT shaping the pigment type and amount.

Melanosomes are transferred from melanocytes to neighboring keratinocytes through dendritic processes, distributing pigment to protect skin cells from ultraviolet radiation.

Development and regulation: Melanocytes originate from neural crest and migrate to their epidermal destinations during embryogenesis. Their activity is regulated by signaling pathways including MC1R receptor activation by alpha-MSH, which raises cAMP and increases tyrosinase activity. Sun exposure stimulates melanin production as a protective response.

Clinical relevance: Disorders include albinism (defects in melanin production), vitiligo (loss of melanocytes in patches), and melanoma, a malignant cancer arising from melanocytes. Variation in skin color results from differences in melanocyte density (generally constant) and, more importantly, the type and amount of melanin produced.