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Melanocyte

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Melanocyte and melanin.

Melanocytes (Template:Pron-en) are cells located in the bottom layer (the stratum basale) of the skin's epidermis, the middle layer of the eye (the uvea)[1], the inner ear[2], meninges[3], bones[4] and heart[5] that produce melanin which is a pigment.

Melanogenesis

Through a process called melanogenesis, these cells produce melanin, which is a pigment found in the skin, eyes, and hair. This melanogenesis leads to a long lasting tan which is in contrast to the tan that originates from oxidation of already existing melanin.[6]

There are both basal and activated levels of melanogenesis; lighter-skinned people generally have low basal levels of melanogenesis. Exposure to UV-B radiation causes an increased melanogenesis due to DNA photodamage.[7]

Since the action spectrum of sunburn and melanogenesis are virtually identical, it is assumed that they are induced by the same mechanism.[8] The agreement of the action spectrum with the absorption spectrum of DNA points towards the formation of cyclobutane pyrimidine dimers (direct DNA damage). The acronym for cyclobutane pyrimidine dimers is CPDs.

Human differences

There are typically between 1000 and 2000 melanocytes per square millimeter of skin. Melanocytes comprise from 5% to 10% of the cells in the basal layer of epidermis. Although their size can vary, melanocytes are typically 7 micrometres in length.

The difference in skin color between fair people and dark people is due not to the number (quantity) of melanocytes in their skin, but to the melanocytes' level of activity (quantity and relative amounts of eumelanin and pheomelanin). This process is under hormonal control, including the MSH and ACTH peptides that are produced from the precursor proopiomelanocortin.

Albinos lack an enzyme called tyrosinase[dubious – discuss]. Tyrosinase is required for melanocytes to produce melanin from the amino acid tyrosine.

Stimulation

Main article: Melanocortin

Numerous stimuli are able to alter melanogenesis, or the production of melanin by cultured melanocytes, although the method by which it works is not fully understood. Melanocortins have been discussed by biologist James D. Watson to have effect on appetite and sexual activity.[9] Vitamin D metabolites, retinoids, melanocyte-stimulating hormone, forskolin, cholera toxin, isobutylmethylxanthine, diacylglycerol analogues, and UV irradiation all trigger melanogenesis and in turn, pigmentation.[10] The production of melanin is also initiated by ACTH (an adrenocorticotropic hormone).

Once made, melanin is moved along arm-like structures called dendrites in a special container called a melanosome which is shipped to the keratinocytes. Melanosomes are vesicles or packages of the chemical inside a plasma membrane. The melanin is in organelles called "melanosomes", that are organized as a cap protecting the nucleus of the keratinocyte.

When ultraviolet rays penetrate the skin and damage DNA, thymidine dinucleotide (pTpT) fragments from damaged DNA will trigger melanogenesis[11] and cause the melanocyte to produce melanosomes, which are then transferred by dendrite to the top layer of keratinocytes.

See also

References

  1. ^ Barden H and Levine S (1983). "Histochemical observations on rodent brain melanin". Brain Res. Bull. 10 (6): 847–851. doi:10.1016/0361-9230(83)90218-6. PMID 6616275.
  2. ^ Markert CL and Silvers WK (1956). "The effects of genotype and cell environment on melanoblast differentiation in the house mouse". Genetics. 41 (3): 429–450. PMID 17247639.
  3. ^ Mintz B (1971). "Clonal basis of mammalian differentiation". Symp. Soc. Exp. Biol. 25: 345–370. PMID 4940552.
  4. ^ Nichols SE and Reams WM (1969). "The occurrence and morphogenesis of melanocytes in the connective tissues of the PET/MCV mouse strain". J. Embryol. Exp. Morphol. 8: 24–32. PMID 14426921.
  5. ^ Theriault LL and Hurley LS (1970). "Ultrastructure of developing melanosomes in C57 black and pallid mice". Dev. Biol. 23 (2): 261–275. doi:10.1016/0012-1606(70)90098-9. PMID 5476812.
  6. ^ tanning tips
  7. ^ Agar N, Young AR (2005). "Melanogenesis: a photoprotective response to DNA damage?". Mutation Research. 571 (1–2): 121–32. doi:10.1016/j.mrfmmm.2004.11.016. PMID 15748643. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |month= ignored (help)
  8. ^ John A. Parrish, Kurt F. Jaenicke, R. Rox Anderson (1982). "Erythema And Melanogenesis Action Spectra Of Normal Human Skin". Photochemistry and Photobiology. 36 (2): 187–191. doi:10.1111/j.1751-1097.1982.tb04362.x.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. ^ Thompson C, Berger A (2000). "Agent provocateur pursues happiness". BMJ (Clinical Research Ed.). 321 (7252): 12. doi:10.1136/bmj.321.7252.12. PMC 1127681. PMID 10875824. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |month= ignored (help)
  10. ^ Roméro-Graillet C, Aberdam E, Biagoli N, Massabni W, Ortonne JP, Ballotti R (1996). "Ultraviolet B radiation acts through the nitric oxide and cGMP signal transduction pathway to stimulate melanogenesis in human melanocytes". The Journal of Biological Chemistry. 271 (45): 28052–6. doi:10.1074/jbc.271.45.28052. PMID 8910416. Retrieved 2009-06-20. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link) CS1 maint: unflagged free DOI (link)
  11. ^ Eller MS, Maeda T, Magnoni C, Atwal D, Gilchrest BA (1997). "Enhancement of DNA repair in human skin cells by thymidine dinucleotides: evidence for a p53-mediated mammalian SOS response". Proceedings of the National Academy of Sciences of the United States of America. 94 (23): 12627–32. doi:10.1073/pnas.94.23.12627. PMC 25061. PMID 9356500. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)

Further reading

  • Ito S (2003). "The IFPCS presidential lecture: a chemist's view of melanogenesis". Pigment Cell Research / Sponsored by the European Society for Pigment Cell Research and the International Pigment Cell Society. 16 (3): 230–6. doi:10.1034/j.1600-0749.2003.00037.x. PMID 12753395. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |month= ignored (help)
  • Millington GW (2006). "Proopiomelanocortin (POMC): the cutaneous roles of its melanocortin products and receptors". Clinical and Experimental Dermatology. 31 (3): 407–12. doi:10.1111/j.1365-2230.2006.02128.x. PMID 16681590. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |month= ignored (help)

External links

Template:Human cell types

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