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Epidermal material from a variety of reptilian species, avian and mammalian scales have been examined by standard histological and x-ray diffraction techniques. It has been found that morphologic and/or tinctorial properties are not good criteria for the identification of specific fibrous protein types. The distribution of fibrous protein types in reptilian epidermal material is very variable, especially in turtles. Lepidosaurian reptiles (the tuatara, snakes and lizards) are unique in showing an alternating vertical distribution of feather and a-type proteins over the entire body surface. The protein distribution in crocodilian scales resembles exactly that found on avian scales. Mammals only possess the a-type protein whatever the nature of the epidermal structure or modification.

Fish skin is a multi-purpose tissue that serves numerous vital functions including chemical and physical protection, sensory activity, behavioural purposes or hormone metabolism. Further, it is an important first-line defense system against pathogens, as fish are continuously exposed to multiple microbial challenges in their aquatic habitat. Fish skin excels in highly developed antimicrobial features, many of which have been preserved throughout evolution, and infection defense principles employed by piscine skin are still operative in human skin. This review argues that it is both rewarding and important for investigative dermatologists to revive their interest in fish skin biology, as it provides insights into numerous fundamental issues that are of major relevance to mammalian skin. The basic molecular insights provided by zebrafish in vivo-genomics for genetic, regeneration and melanoma research, the complex antimicrobial defense systems of fish skin and the molecular controls of melanocyte stem cells are just some of the fascinating examples that illustrate the multiple potential uses of fish skin models in investigative dermatology. We synthesize the essentials of fish skin biology and highlight selected aspects that are of particular comparative interest to basic and clinically applied human skin research.

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