Melanocyte

Melanocytes (including melanocytes, melanophores, Ez the melanophore, the melanophores ) are the pigment cells of the skin and lie there in the basal cell layer of the epidermis and the hair follicles. They synthesize melanin and enter this in the form of so-called melanosomes to the surrounding keratinocytes from. Melanin is a significant protection of the skin against ultraviolet radiation dar. melanin producing cells to the surrounding keratinocytes form a so-called Melanozyteneinheit.

The skin color is not due to a proliferation of melanocytes, but rather by a longer stay of melanosomes in keratinocytes.

Histology

The melanocytes located in the basal cell layer (stratum basale) directly on the basement membrane and are connected thereto via hemidesmosomes. Melanocytes are found in relatively low numbers and are with their cytoplasmic branches ( dendrites ) with about 5-8 keratinocytes loosely connected. Melanocytes are metabolically active and have numerous mitochondria, rough endoplasmic reticulum, a strong and a large Golgi apparatus. Melanocytes are also found in the choroid of the eye, the iris of the eye, the oral mucosa and in other places. It should be noted that these specific melanocytes do not form Melanozyteneinheiten with the surrounding cells and usually also make no melanosomes to their environment. Immunohistochemistry melanocytes are S-100 positive. Histochemically to stain melanocytes upon incubation in DOPA solution black - brown (melanin ) to.

Embryology

The Melanozytenvorläufer ( melanoblasts ) migrate during embryonic development from the neural crest into the skin. Melanocytes are thus descendants of the neuroectoderm.

Melanin synthesis and distribution

The formation of melanin, referred to as melanogenesis, involves the synthesis of the first inactive enzyme tyrosinase. This is synthesized in the rough endoplasmic reticulum and accumulates in the Golgi apparatus, which then pinches in vesicles. The activation of tyrosinase via UV light. After further maturation of the vesicles can be melanin and demonstrate crystalline inclusions in the electron microscope. At this stage it is called the vesicles " Prämelanosomen ". In the vesicles, the amino acid tyrosine accumulates, which is ultimately converted to melanin by the tyrosinase in DOPA and intermediate steps. Also in this case the protein Trp -1 plays a role. After further aging the Prämelanosom loses its internal structure, and is referred to as " mature melanosome ". The mature melanosomes migrate into the cytoplasmic extensions of the melanocytes and are emitted to the surrounding cells. The surrounding cells take the melanosomes directly and store them in an own cytoplasm.

Regulation of melanin synthesis

• Ultraviolet radiation: Under UV exposure results in activation of melanocytes and melanosomes are increasingly released ( tanning )
• MSH ( melanocyte- stimulating hormone, melanotropin ) MSH also leads to the activation of melanocytes. When Addison's disease, among others, increased MSH is produced, which is reflected in an increased skin tanning.

Diseases

A decrease of melanocytes or a decreased melanin synthesis lead to hypopigmentation. In the following illnesses melanocytes or melanocyte precursors play an important role:

• Vitiligo
• Melanoma (skin melanoma, choroidal melanoma, conjunctival melanoma)
• Dysplastic nevus
• Lentigo
• Hyperpigmentation
• Nevus
• Albinism
• Leucism
• Spotting