6 - The Neural Crest: Source of the Pigment Cells

Summary

The bright colors and the striking variety of patterns that characterize the skin and coat of many vertebrate species have long been a subject of interest and wonder. It seems that the first scientific studies of animal coloration started in the middle of the nineteenth century about the color changes of the African chameleon (see Bagnara and Hadley, 1973). Pertinent questions were raised concerning the physiological mechanisms underlying animal pigmentation, while chemists and physicists became interested in the nature of pigments. It was understood that some colorations resulted from the structural state of the biological material. Thus, it became apparent that the spectacular iridescent properties of certain insects and birds are not due to the presence of blue or green pigments but rather are the result of physical phenomena. Iridescent colors are produced when biological structures, such as fibrils and lamellae, are orderly arranged to generate light diffraction. Another phenomenon responsible for 'structural coloration” results from differential scattering of light, which provides the basis for much of the blue colors seen in eyes, feathers, and skins of certain vertebrates.

By analyzing extracts of colored tissues, chemists discovered that lipidsoluble yellow, orange or red pigments of animals are carotenoids, while guanine deposits are responsible for the whitish reflecting surfaces of fishes and frogs. Most importantly, melanins, flavins, pteridines, and porphyrins were recognized as essential compounds in animal pigmentation.