Differentiation of snake epidermis, with emphasis on the shedding layer

Little is known about specific proteins involved in keratinization of the epidermis of snakes. The presence of histidine‐rich molecules, sulfur, keratins, loricrin, transglutaminase, and isopeptide‐bonds have been studied by ultrastructural autoradiography, X‐ray microanalysis, and immunohistochemistry in the epidermis of snakes. Shedding takes place along a shedding complex, which is composed of two layers, the clear and the oberhautchen layers. The remaining epidermis comprises different layers, some of which contain beta‐keratins and others alpha‐keratins. Weak loricrin, transglutaminase, and sometimes also iso‐peptide‐bond immunoreactivities are seen in some cells, lacunar cells, of the alpha‐layer. Tritiated histidine is mainly incorporated in the shedding complex, especially in dense beta‐keratin filaments in cells of the oberhautchen layer and to a small amount in cells of the clear layer. This suggests the presence of histidine‐rich, matrix proteins among beta‐keratin bundles. The latter contain sulfur and are weakly immunolabeled for beta‐keratin at the beginning of differentiation of oberhautchen cells. After merging with beta cells, the dense beta‐keratin filaments of oberhautchen cells become immunopositive for beta‐keratin. The uptake of histidine decreases in beta cells, where little dense matrix material is present, while pale beta‐keratin filaments increase. During maturation, little histidine labeling remains in electron‐dense areas of the beta layer and in those of oberhautchen spinulae. Some roundish dense granules of oberhautchen cells rich in sulfur are negative to antibodies for alpha‐keratin, beta‐keratin, and loricrin. The granules eventually merge with beta‐keratin, and probably contribute to the formation of the resistant matrix of oberhautchen cells. In conclusion, beta‐keratin, histidine‐rich, and sulfur‐rich proteins contribute to form snake microornamentations. J. Morphol. © 2005 Wiley‐Liss, Inc.