Everything about Melanocyte totally explained
Melanocytes are
cells located in the bottom layer (the
stratum basale) of the skin's
epidermis and in the middle layer of the eye (the
uvea).
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.
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 the DNA photodamage that's generated by UV-B.
Since the action spectrum of
sunburn and melanogenesis are virtually identical, it's assumed that they're 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 (
direct DNA damage). The
acronym for cyclobutane pyrimidine dimers is CPD's.
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.
Albinos lack an enzyme called
tyrosinase. Tyrosinase is required for melanocytes to produce melanin from the
amino acid tyrosine.
Embryology
Embryologically, melanocytes are derived from the
neural crest, which is a completely different source than that of the surrounding skin cells (
keratinocytes).
All melanocytes have the capacity to migrate widely in the embryo. Therefore, a cancer of a melanocyte (which is called a
melanoma) will spread (
metastasize) very easily. For this reason, melanomas are often fatal. When melanomas are surgically removed, much of the surrounding tissue must be taken as well.
Stimulation
Numerous stimuli are able to alter melanogenesis, or the production of melanin by cultured melanocytes, although the method by which it works isn't fully understood.
Vitamin D metabolites,
retinoids,
melanocyte-stimulating hormone (ie:
Melanotan),
forskolin,
cholera toxin,
isobutylmethylxanthine,
diacylglycerol analogues, and UV irradiation all trigger melanogenesis and in turn, pigmentation. 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 and cause the melanocyte to produce
melanosomes, which are then transferred by dendrite to the top layer of
keratinocytes.
Further Information
Get more info on 'Melanocyte'.
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