|MadSci Network: Cell Biology|
My short answer to this question is: No or most probably not. Melanin is a natural pigment that is generated by melanocytes. Melanocytes were once migratory cells derived from neural crest cells during embryogenesis. Some people have areas of absent skin pigmentation because the clonal ancestor of neural crest cells died before it could migrate to the specific region of skin where it was programmed to diferentiate into a melanocyte. The distribution of these areas of absent pigmentation resembles the "dermatome maps" of spinal cord sensory neurons. This is because neural crest cells also lead to development of peripheral nerve cells. The melanin pigment manufactured by melanocytes remains within endosomes (vacuoles) in the cytoplasm of these cells. If you were to inject melanin pigment into the skin you would not be able to control its distribution as well as the distribution of melanocytes controls distribution of cytoplasmic pigment. It would take an enormous amount of small needle pricks to accomplish this. The pain by itself might prevent someone from doing this. Furthermore, there would be no certainty that the pigment would stay where it was injected. Since melanin is a natural material, cells could engulf it and carry it away, were it deposited in the extracellular matrix. Some cells might concentrate it in phagocytic vacuoles which would yield dark dots of pigment surrounded by unpigmented areas. Using existing Tattoo pigments might be more successful in darkening patches of nonpigmented skin, but there would be a cost of lots of pain. While it is not possible at present to cause melanocytes to develop in areas where they are missing, it may be possible to stimulate existing melanocytes to make more melanin. This is what happens when people get a sun tan.
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