Pigmentary Abnormalities

Question 1

Why do we need pigment cells?

Answer 1

Melanocytes synthesize melanin in melanosomes.

Keratinocytes that make hair also take melanin from melanocytes, which are located at the base of hair follicles.

Question 2

What are Melanocytes?

Answer 2

The pigment producing cells in vertebrates.

• neural crest cell derivative with relationships to neurons and glia/schwann cells during development
• found in the skin, eyes, inner ears, heart, and meninges of the central nervous system in mammals.
• In the epidermis, melanocytes produce melanin and transfer it to neighboring keratinocytes to pigment the skin.

Question 3

What are melanosomes?

Answer 3

Specialized organelles that synthesize melanin

Question 4

Describe the formation process of melanosomes in a melanocyte

Answer 4

Melanosomes go through several stages of formation in the endosome, first laying down a structural framework, then synthesizing melanin on top of it. Everything that is needed is imported into the melanosome. The mature melanosomes travel down the dendrites along microtubules and are ingested by the keratinocytes through phagocytosis of the dendritic tips. The melanosomes then cluster over the nuclei of the keratinocytes, protecting them from DNA damage.

Question 5

Why does skin get darker after exposure to UV light? What is this called?

Answer 5

In the TANNING RESPONDE, UV light causes DNA damage, which stimulates the p53 response pathway. If the damage is not too bad and the cell survives, the temporary p53 stabilization upregulates the expression of POMC, which is cleaved into several different signaling molecules including alpha-MSH

Question 6

What is alpha-MSH? What does it do?

Answer 6

alpha- MSH is a melanocyte stimulating hormone that binds a G protein coupled receptor on the surface of melanocytes called Mc1R (the melanocortin 1 receptor). This heterotrimeric G protein coupled receptor increases cAMP levels inside the cell, which increases the expression of genes that regulate pigment production. The increased melanin acts as an optical shield to decrease DNA damage in skin cells.

Question 7

What affects differences in skin colour between people?

Answer 7

1. differences in the amount of melanin,
2. the size of the melanosomes
3. How melanosomes are distributed within a cell (contained by a membrane in clusters or single),
4. ratio of melanin types (eumelanin and pheomelanin).