Melanocytes


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Melanocytes

 

in vertebrates and man, pigment cells that synthesize melanins.

There are two kinds of melanocytes: free melanocytes and epithelial melanocytes. Free melanocytes, which are found in the skin, hair follicles, meninges, choroid, and stroma of the iris, originate from the neural crests. When the neural tube closes, they migrate to different parts of the body in the form of mobile, colorless cells, or melanoblasts—the precursors of melanocytes. Epithelial melanocytes, which are found in the pigmented epithelium of the retina, iris, and ciliary folds of the eye, originate from cells of the rudimentary eye.

Melanins are synthesized in the melanocytes in special organelles, or melanosomes, which contain the enzyme tyrosinase. After they fill with melanin, the melanosomes become enzymatically inert pigment granules. The number, shape, and intensity of color of these granules, like the general color of the body, are genetically controlled. Melanocytes are colorless in albinos, in which melanins are not synthesized because of an absence of active tyrosinase.

O. G. STROEVA

References in periodicals archive ?
The paracrine role of stem cell factor/c-KIT signaling in the activation of human melanocytes in ultraviolet-B-induced pigmentation.
Nevi of Ota have been classified histologically into 5 types based on the locations of the dermal melanocytes, which are (1) superficial, (2) superficial dominant, (3) diffuse, (4) deep dominant, and (5) deep.
The binding of melanocyte-stimulating hormone to the melanocortin 1 receptor sets in motion melanogenesis by activating tyrosinase in melanocytes.
Raising levels of ALX3 in cells interfered with activity of a gene called Mitf, a master regulator of pigment production and melanocyte maturation.
Coat color depends on the amounts and types of melanin produced by melanocytes in the hair follicles (Ito and Wakamatsu, 2008).
3] Unlike cutaneous melanomas, primary mucosal melanomas arise from melanocytes located in occult sites and can present along the mucosal membranes lining respiratory, gastrointestinal, and urogenital tract.
In experiments in mice and human cells, researchers at NYU Langone Medical Center found that control of these skin and early-stage hair cells, known as melanocyte stem cells, is regulated by cell-to-cell signaling reactions.
Hair follicle and skin tissue, apart from the bone marrow, are perhaps the only tissues, which have got the niche for diverse kind of stem cells called as melanocyte stem cells, keratinocyte stem cells, and mesenchymal stem cells," said Dr Mohanty.
They found that control of these cells, known as melanocyte stem cells, is regulated by two key signalling pathways - part of the endothelin receptor type B (EdnrB) and Wnt signalling pathways.
Currently, the generally accepted hypothesis of the cause of vitiligo is the autoimmune one, according to which the destruction of melanocytes in vitiligo lesions is induced by autoimmune mechanisms (1-3).
Autoimmune theory showed that melanocytes are killed by autoimmune effector mechanisms, either memory cytotoxic T cells or autoantibodies directed to melanocyte surface antigens, as a result of tolerance breakage [9].
Melanoma is a malignant tumor of melanocytes that is predominantly found in the skin.

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