Making Waves with Hairs

Abstract

The skin is like a canvas. Pigment distribution, skin appendages, skin ridges, etc. are arranged on the skin surface. The arrangement may be random but every now and then they form specific patterns. In some occasions, the specific arrangement is important for organism function or message display. In all occasions, these distinct arrays provide us with windows into the fundamental processes of pattern formation. Skin patterns can be studied by non-invasive visual observations, and dynamic changes can be recorded in vivo for analyses. The hair distribution pattern consists of multiple hair primordia with different developmental stages, directionality, and spacing. Hair primordia on the skin can be randomly distributed, de-synchronized in hair cycling, or coordinated to give rise to a higher level pattern. When there are incremental changes of developmental stages or hair orientation from one primordium to the next, they give the impression of a wave. These waves can be parallel to each other and form stripes or radiate out from focal centers, thus forming whorls as seen in fingerprints and hair patterns on the scalp. Do these patterns result from precise genetic coding or self-organizing cellular events? Patterns such as fingerprints have similar attributes (similar width, organization plan) but they are non-identical (with enough difference to be used as individual identifiers). In fact fingerprints among monozygotic twins, while more similar than nonrelated individuals, are still different (Jain et al, 2002). Thus there is a non-genetic component in the formation of fingerprints. The hair whorls in the scalp of monozygotic twins have not been documented previously and in this issue there is a case report (Paine et al, 2004).