Immunocytochemical analysis of beta (β) keratins in the epidermis of chelonians, lepidosaurians, and archosaurians

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Abstract
Beta (β) keratins are present only in the avian and reptilian epidermises. Although much is known about the biochemistry and molecular biology of the β keratins in birds, little is known for reptiles. In this study we have examined the distribution of β keratins in the adult epidermis of turtle, lizard, snake, tuatara, and alligator using light and electron immunocytochemistry with a well-characterized antiserum (anti-β1 antiserum) made against a known avian scale type β keratin. In lizard, snake, and tuatara epidermis this antiserum reacts strongly with the beta-layer, more weakly with the oberhautchen before it merges with the beta-layer, and least intensely with the mesos layer. In addition, the anti-β1 antiserum reacts specifically with the setae of climbing pads in gekos, the plastron and carapace of turtles, and the stratum corneum of alligator epidermis. Electron microscopic studies confirm that the reaction of the anti-β1 antiserum is exclusively with characteristic bundles of the 3-nm β keratin filaments in the cells of the forming beta-layer, and with the densely packed electron-lucent areas of β keratin in the mature bet- layer. These immunocytochemical results suggest that the 3-nm β keratin filaments of the reptilian integument are phylogenetically related to those found in avian epidermal appendages.