Cyclic oscillations in melanin composition within hairs of baboons.

Abstract

The wild-type agouti-banding pattern for hair is well characterized in lower mammals such as mice. The switch between eumelanin and pheomelanin in bands in the hair results from the interaction of alpha-melanocyte stimulating hormone and agouti signal protein through the melanocortin 1 receptor on melanocytes. However, such banding patterns have not been described to date in higher mammals. We now report such 'agouti'-banding patterns that occur in several subspecies of baboons, and characterize those hairs using chemical and immunohistochemical methods. Hair and skin samples were obtained from the dorsa of adult male baboons of different subspecies (Papio cynocephalus hamadryas (PCH) and Papio cynocephalus anubis (PCA)). The hairs were excised with scissors into the gray and the white bands of the PCH subspecies and into the black and the yellow bands of the PCA subspecies, and were analyzed for total melanin, eumelanin, and pheomelanin by spectrophotometric and chemical methods. Hairs in the PCA subspecies oscillate between a eumelanic band (with high melanin content) and a pheomelanic band, while hairs in the PCH subspecies oscillate between a eumelanic band (with low melanin content) and a non-pigmented band. Those chemical data are consistent with the histological appearance of the hair bulbs stained by the Fontana-Masson technique. The difference in the melanin content between PCH and PCA subspecies is most likely related to tyrosinase levels, as suggested by the presence of unpigmented muzzle in the PCH subspecies compared with the black muzzle in the PCA subspecies.