What causes albinism?
Researchers have revealed why people with defects in a protein called OCA2 are unable to make melanin.
Melanin is a pigment found in our skin, eyes and hair. Individuals who are unable to make or store melanin, a condition known as albinism, have unusually pale features and problems with vision. The pigment helps to protect us from harmful UV radiation, and so individuals with albinism also have an increased risk of developing skin and eye cancers.
In cells, melanin is made and stored in compartments called melanosomes. The most common type of albinism is caused by defects in a protein called OCA2, which is found in the membrane that surrounds melanosomes. However the role of OCA2 in melanin production is unclear.
It has been proposed that OCA2 may allow charged particles (or ions) to enter or leave melanosomes. Now, Nicholos Bellono and co-workers used a technique called patch-clamp to study the movement of ions across the membrane of melanosomes from skin and eye cells. The experiments show that a flow of chloride ions out of the melanosome is required for melanin to be produced. OCA2 is involved in the ion movement, and it might alter the acidity of the melanosome when present.
Bellono and co-workers propose that OCA2 is part of an ion channel that allows chloride ions to pass through the membrane, to make the melanosome less acidic and enable melanin to be produced. The next challenge will be to identify other ion channels in the melanosome and understand their roles in producing melanin.
To find out more
Read the eLife research paper on which this story is based: “An intracellular anion channel critical for pigmentation” (December 16, 2014).
eLife is an open-access journal that publishes outstanding research in the life sciences and biomedicine.
