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Melanocyte
 
 
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Melanocytes are cells
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
 located in the bottom layer (the stratum basale) of the skin's epidermis
Epidermis (skin)

The epidermis is the outermost layer of the skin, composed of terminally differentiated stratified squamous epithelium, acting as the body's major barrier against an inhospitable environment....
, the middle layer of the eye (the uvea
Uvea

The uvea , also called the uveal layer, uveal coat, uveal tract, or vascular tunic, is the pigmented middle of the three concentric layers that make up an eye....
), the inner ear, meninges, bones and heart.

melanocyte is a cell derived from the neural crest. During embryogenesis, the melanocyte migrates to the epidermis, hair follicles, eye (choroid, ciliary body and iris), inner ear (stria vascularis), and the leptomeninges (medulla).






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Melanocytes are cells
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
 located in the bottom layer (the stratum basale) of the skin's epidermis
Epidermis (skin)

The epidermis is the outermost layer of the skin, composed of terminally differentiated stratified squamous epithelium, acting as the body's major barrier against an inhospitable environment....
, the middle layer of the eye (the uvea
Uvea

The uvea , also called the uveal layer, uveal coat, uveal tract, or vascular tunic, is the pigmented middle of the three concentric layers that make up an eye....
), the inner ear, meninges, bones and heart.

Embryology

The melanocyte is a cell derived from the neural crest. During embryogenesis, the melanocyte migrates to the epidermis, hair follicles, eye (choroid, ciliary body and iris), inner ear (stria vascularis), and the leptomeninges (medulla). This common ancestry in the neural crest becomes evident in congenital disorders such as Waardenburg syndrome, which often presents with deafness, leukoderma, and ocular pigmentary alterations (heterochromia irides). Melanocyte death in diseases like Vogt-Koyanagi-Harada syndrome similarly manifests with aseptic meningitis, vitiligo and deafness. All melanocytes have the capacity to migrate widely in the embryo. Therefore, a cancer of a melanocyte (which is called a melanoma
Melanoma

Melanoma is a malignant tumor of melanocytes which are found predominantly in skin but also in the bowel and the eye . It is one of the rarer types of skin cancer but causes the majority of skin cancer related deaths....
) 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.

Melanogenesis

Through a process called melanogenesis, these cells produce melanin
Melanin

Melanin is a class of compounds found in the plant, animal, and protista kingdom , where it serves predominantly as a pigment. The class of pigments are derivatives of the amino acid tyrosine....
, which is a pigment found in the skin
Skin

The skin is the outer covering of the body, also known as the epidermis. It is the largest organ of the integumentary system made up of multiple layers of epithelial biological tissue, and guards the underlying muscles, bones, ligaments and organ s....
, eye
Eye

Eyes are Organ that detect light, and send signals along the optic nerve to the visual system and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system....
s, and hair
Hair

Hair is a protein filament that epidermal growth from hair follicle deep within the dermis. The fine, soft hair found on many nonhuman mammals is typically called fur; wool is the characteristically curly hair found on sheep and goats....
. 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 DNA photodamage.

Since the action spectrum of sunburn
SunBurn

SunBurn is a regional event held in Florida. Although SunBurn has its roots in the annual Burning Man festival in Nevada, it is not an official Burning Man event, because the organizers of SunBurn do not condone the direction that the Burning Man Organization has taken over the years....
 and melanogenesis are virtually identical, it is assumed that they are 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
Direct DNA damage

Direct DNA damage can occur when DNA directly absorbs the UV-B-photon. UVB light causes thymine base pairs next to each other in genetic sequences to bond together into thymine dimers, a disruption in the strand which reproductive enzymes cannot copy....
). 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
Human skin color

Human skin color can range from almost black to nearly colorless in different homo sapiens. Skin color is determined by the amount and type of melanin, the pigment in the skin....
 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).

Albinos lack an enzyme called tyrosinase
Tyrosinase

Tyrosinase is an enzyme that Catalysis the oxidation of phenols and is widespread in plants and animals. Tyrosinase is a copper-containing enzyme present in plant and animal tissues that catalyzes the production of melanin and other pigments from tyrosine by oxidation, as in the blackening of a peeled or sliced potato exposed to air....
. Tyrosinase is required for melanocytes to produce melanin from the amino acid
Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
 tyrosine
Tyrosine

Tyrosine or 4-hydroxyphenylalanine, is one of the 20 amino acids that are used by cell to protein biosynthesis proteins. This is a non-essential amino acid and it is found in casein....
.

Stimulation

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
James D. Watson

James Dewey Watson is an American molecular biology, best known as one of the co-discoverers of the structure of DNA. Watson, Francis Crick, and Maurice Wilkins were awarded the 1962 Nobel Prize in Physiology or Medicine "for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer...
 to have effect on appetite and sexual activity. Vitamin D
Vitamin D

Vitamin D is a group of fat-soluble prohormones, the two major forms of which are vitamin D2 and vitamin D3 . The term vitamin D also refers to metabolites and other analogues of these substances....
 metabolites, retinoids, melanocyte-stimulating hormone
Melanocyte-stimulating hormone

The melanocyte-stimulating hormones are a class of peptide hormones that in nature are produced by cells in the intermediate lobe of the pituitary gland....
 (ie: Melanotan
Melanotan

Melanotan may refer to:* Afamelanotide, originally developed under the names "Melanotan 1" or "Melanotan I", a drug currently in development in implant form as a prophylactic treatment for a series of skin disorders and potential skin cancer preventative agent...
), forskolin
Forskolin

Forskolin is a labdane diterpene that is produced by the Indian Coleus plant . Forskolin is commonly used to raise levels of cyclic AMP in the study and research of cell physiology....
, cholera toxin
Cholera toxin

Cholera toxin is a protein complex secreted by the bacterium Vibrio cholerae. CTX is responsible for the harmful effects of cholera infection....
, isobutylmethylxanthine, diacylglycerol
Diglyceride

A diglyceride, or a diacylglycerol , is a glyceride consisting of two fatty acid chains covalent bond to a glycerol molecule through ester linkages....
 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
Melanosome

In a Cell , a melanosome is an organelle containing melanin, the most common light-absorbing pigment found in the animal kingdom.Cells that contain melanosomes are called melanocytes, and also the retinal pigment epithelium cells, whereas cells that have merely engulfed the melanosomes are called melanophages....
 which is shipped to the keratinocytes. Melanosomes are vesicle
Vesicle

Vesicle may refer to:* Synaptic vesicle* Auditory vesicle* Optic vesicles* Seminal vesicle* Subsporangial vesicle* Vesical arteries* Vesicle , a relatively small and enclosed compartment within a cell...
s or packages of the chemical inside a plasma membrane. The melanin is in organelles called "melanosome
Melanosome

In a Cell , a melanosome is an organelle containing melanin, the most common light-absorbing pigment found in the animal kingdom.Cells that contain melanosomes are called melanocytes, and also the retinal pigment epithelium cells, whereas cells that have merely engulfed the melanosomes are called melanophages....
s", that are organized as a cap protecting the nucleus of the keratinocyte
Keratinocyte

The keratinocyte is the major constituent of the epidermis , constituting 95% of the cells found there. Those keratinocytes found in the Stratum germinativum are sometimes referred to as "basal cells" or "basal keratinocytes."...
.

When ultraviolet rays penetrate the skin and damage DNA, thymidine
Thymidine

Thymidine is a chemical Chemical compound, more precisely a pyrimidine deoxynucleoside. Deoxythymidine is the DNA nucleoside T, which pairs with deoxyadenosine in double-stranded DNA....
 dinucleotide (pTpT) fragments from damaged DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
 will trigger melanogenesis and cause the melanocyte to produce melanosome
Melanosome

In a Cell , a melanosome is an organelle containing melanin, the most common light-absorbing pigment found in the animal kingdom.Cells that contain melanosomes are called melanocytes, and also the retinal pigment epithelium cells, whereas cells that have merely engulfed the melanosomes are called melanophages....
s, which are then transferred by dendrite to the top layer of keratinocyte
Keratinocyte

The keratinocyte is the major constituent of the epidermis , constituting 95% of the cells found there. Those keratinocytes found in the Stratum germinativum are sometimes referred to as "basal cells" or "basal keratinocytes."...
s.

See also

  • Chromatophore
    Chromatophore

    Chromatophores are Biological pigment-containing and light-reflecting cell found in amphibians, fish, reptiles, crustaceans, and cephalopods. They are largely responsible for generating skin and eye color in cold-blooded animals and are generated in the neural crest during embryonic development....
     (the pigment cell type
    Cell type

    A cell type is a distinct morphological or functional form of cell . When a cell switches state from one cell type to another, it undergoes cellular differentiation....
     found in cold blooded animals)
  • Eye color
    Eye color

    Eye color is a polygenic trait and is determined by the amount and type of pigments in the eye's Iris . Humans and animals have many phenotypic variations in eye color....
  • Melanoma
    Melanoma

    Melanoma is a malignant tumor of melanocytes which are found predominantly in skin but also in the bowel and the eye . It is one of the rarer types of skin cancer but causes the majority of skin cancer related deaths....
  • tanning activator
    Tanning activator

    Tanning activators are chemicals that increase the effect of UV-radiation on the human skin. Since sunburn and sun tanning are induced by the same mechanism these substances increase the likelihood for sunburn as well....


External links

- "Eye: fovea, RPE" - "Integument: pigmented skin"