Agouti signalling protein

Where it comes from

Made in

Dermal cells beneath hair follicles; in people, skin, fat tissue and testis

Sent out by

In a pulse during the hair cycle in mice, which gives the banded agouti hair; steadier in people

Acts on

• Melanocytes (pigment type)
• Fat tissue
• Hypothalamus, in the mutant mouse only

What it does

• Turns melanocytes from making black-brown eumelanin to red-yellow pheomelanin
• Shapes the agouti coat of wild mice and the pattern of many mammals
• In the yellow obese mouse, which expresses it everywhere, it blocks MC4R in the brain and causes obesity

In medicine

• No medicine of its own; it is pigment genetics that brings it up in people
• Variants near ASIP are associated with red hair and freckling ³, and with a raised risk of melanoma and basal cell carcinoma in Europeans ²

Beyond the body’s own use

• Not a treatment and not in trials. The receptors it blocks are the drug targets instead: setmelanotide at MC4R and afamelanotide at MC1R push the signal the other way
• What it does in adult people is still open: it is made in skin, fat and testis, while the pulse that bands a mouse’s hair has no human counterpart ¹