Pigment cells

Melanocytes are melanin-producing neural crest-derived cells located in the bottom layer (the stratum basale) of the skin's epidermis, the middle layer of the eye (the uvea), the inner ear, vaginal epithelium, meninges, bones, and heart. Melanin is a dark pigment primarily responsible for skin color. Once synthesized, melanin is contained in special organelles called melanosomes which can be transported to nearby keratinocytes to induce pigmentation. Functionally, melanin serves as protection against UV radiation. Melanocytes also have a role in the immune system. Melanocytes are melanin-producing neural crest-derived cells located in the bottom layer (the stratum basale) of the skin's epidermis, the middle layer of the eye (the uvea), the inner ear, vaginal epithelium, meninges, bones, and heart. Melanin is a dark pigment primarily responsible for skin color. Once synthesized, melanin is contained in special organelles called melanosomes which can be transported to nearby keratinocytes to induce pigmentation. Functionally, melanin serves as protection against UV radiation. Melanocytes also have a role in the immune system. Through a process called melanogenesis, melanocytes produce melanin, which is a pigment found in the skin, eyes, hair, nasal cavity, and inner ear. This melanogenesis leads to a long-lasting pigmentation, which is in contrast to the pigmentation that originates from oxidation of already-existing melanin. There are both basal and activated levels of melanogenesis; in general, lighter-skinned people have low basal levels of melanogenesis. Exposure to UV-B radiation causes increased melanogenesis. The purpose of melanogenesis is to protect the hypodermis, the layer under the skin, from damage by UV-B radiation. The color of the melanin is black, allowing it to absorb a majority of the UV-B light and block it from passing through the epidermis. Since the action spectrum of sunburn and melanogenesis are virtually identical, they are assumed to be induced by the same mechanism. The agreement of the action spectrum with the absorption spectrum of DNA points towards the formation of cyclobutane pyrimidine dimers (CPDs) - direct DNA damage.