Melanocytes: What are they? Melanin, Melanogenesis and Melanin Absence

They are melanin-producing cells found mainly in the lower part of the upper layer of the skin.

Melanin is a well-known pigment and the main responsible for giving color to our skin (light, medium and dark skin tones).

There are two types of melanocytes: differentiated melanocytes and retinal pigment epithelium (RPE).

The former are found in various body parts, including the skin, while the latter only appears as a single layer of cells behind the retina.

While differentiated melanocytes originate from embryonic neural crest cells in the growing embryo, RPE develops in situ from the optic cup of the brain.

The typical primary human epidermal melanocytes (NHEM) are isolated from the epidermis of the juvenile foreskin or adult skin in different places, such as the face, breasts, abdomen, and thighs.

They are located in the basal layer but branch out between the keratinocytes in suprabasal layers. About 5-10% of the cells in the epidermis are melanocytes.


The main objective of melanocytes in the production of melanin, the protein responsible for the pigmentation of the skin, eyes, and hair. Melanin protects the skin cells and deeper layers from the dangerous effects of UV radiation.

It is produced and stored in melanosomes, which are located near the membrane of the melanocytes but can also be transferred to neighboring keratinocytes.

The melanocytes are isolated using the melanocyte growth medium containing PMA (phorbol myristate acetate) free of serum or the serum-free melanocyte growth medium and free of PMA M2.

Since PMA is a tumor-promoting mitogen, it can interfere with experimental approaches. Therefore, we recommend using isolated cells in Melanocyte Growth Medium M2 and using this medium for culture.

Although better known as loyal residents and workers of our skin, differentiated melanocytes are found in various places around the body.

From parts of the eye and hair follicles to the inner ear, to the two innermost layers of the meninges in the brain (the leptomeninges), to the valves and septa of the heart, lungs, and even fatty tissue.

Why pigment-producing cells would be so ubiquitous is a hotly debated topic.

What is melanin, and what does it do?

Melanin is the pigment that gives color to hair, skin, and eyes. People with darker skin have more melanin than those with lighter skin. There are three types of melanin:

Eumelanin is a dark brown that is found in the hair, skin, and eyes and protects against UV radiation (lower amounts in the hair follicles are responsible for blonde hair); Neuromelanin in the brain and pheomelanin pale red or yellowish, is found in hair and skin (responsible for red hair!).

The production of pigments in the skin is regulated by a peptide hormone of the pituitary gland called melanocyte-stimulating hormone (MSH).

Melanocytes produce and store melanin in organelles called melanosomes in response to MSH secretion. The process by which melanin is created is called melanogenesis.

The biochemical pathways of melanogenesis that result in melanin production involve a cascade of phosphorylation-driven protein activations. The pigment is transferred from the melanocytes by the melanosomes. These small pockets travel to the long tendrils of the cell, known as dendrites.

Melanin is secreted to neighboring keratinocytes. The result is a long-lasting pigmentation. In general, a melanocyte is associated with several epidermal keratinocytes. Together they form what are called epidermal melanin units.

What gives you a tan?

There are basal levels and induced or activated melanogenesis. In general, people with lighter skin have lower baseline levels of melanin production than people with darker skin.

When your skin is exposed to UV-B rays, melanocytes are activated at full speed and produce higher melanin levels. Darkened skin is better protected from photodamage because darker colors absorb light.

That is why tanning can be dangerous since before your body produces the pigment, you expose your cells to UV radiation. Prolonged exposure to the sun is a factor that increases the likelihood of contracting skin cancer.

After tanning, the skin is better protected, but damage to UV rays is still possible and equally dangerous, so be sure to bring your summer hat to the beach.

Melanocytes are not the only cells in the body capable of producing melanin. The cells of the pigmented epithelium of the retina, the epithelium of the iris, and the ciliary body of the eye, some neurons, and adipocytes can also.

What happens when melanin production goes into overdrive or is absent?

The aberrant production of melanin, whether too high, too low, or absent, is responsible or plays a role in many skin-related conditions and diseases.

Including birthmarks, moles, vitiligo, albinism, phenylketonuria, Waardenburg syndrome, age spots, freckles, gray hair, and melanomas.