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Skin-nontumor / Clinical Dermatology

General

Melanocytes


Reviewer: Mowafak Hamodat MB.CH.B, MSc., FRCPC, Memorial University of Newfoundland (see Reviewers page)
Revised: 24 August 2011, last major update August 2010
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.

General
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● Neural crest origin
● In basal epidermis, hair follicles, most squamous mucous membranes, leptomeninges
● The ratio of melanocytes to basal cells ranges from approximately 1:4 on the cheek to 1:10 on the limbs
● Contain dendrites, delicate cytoplasmic processes that extend between keratinocytes
● Upwards or lateral migration within epidermis or into papillary dermis does not necessarily indicate malignancy
● Cytoplasm is clear due to retraction, nuclei typically are smaller and slightly more hyperchromatic than nuclei of adjacent keratinocytes, have uniform chromatin, indented nuclear contour, no nucleoli
● Produce melanin from tyrosine, transfer it (via cytocrinia) to adjacent epithelial cells to protect against ultraviolet rays
● Racial skin color is due to amount of melanin in keratinocytes, not number of melanocytes

Drawings
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Skin and melanocytes

Positive stains
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● Fontana-Masson, tyrosinase, S100, NSE, MelanA/Mart1, microphthalmia transcription factor, vimentin, bcl2, HMB45 (activated melanocytes)
● Variable keratin in activated melanocytes

Negative stains
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● GFAP, neurofilament; HMB45 and keratin in resting melanocytes

Electron microscopy
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● Melanosomes: melanin-synthesizing organelle derived from Golgi

Differential diagnosis
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Melanoblasts: immature counterpart
Melanophages: macrophages with ingested melanin

Additional references
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Wikipedia, American Academy of Dermatology

End of Skin-nontumor / Clinical Dermatology > General > Melanocytes


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