Differentiation of the epidermis in turtle: an immunocytochemical, autoradiographic and electrophoretic analysis

Proteins involved in the process of cornification of turtle epidermis are not well known. The present immunocytochemical, electrophoretic and autoradiographic study reports on the localization patterns and molecular weights of keratins, which are cornification proteins, and of tritiated histidine in turtle epidermis. Alpha-keratins with a molecular weight of 40-62 kDa are present in the epidermis. Beta-keratin is mainly detectable in the stratum corneum of the carapace and plastron, but is rarely present or even absent in the corneous layer of limb, tail and neck epidermis. After electrophoresis and immunoblotting with an antibody against chicken scale beta-keratin, bands at 15-17, 22-24, and 36-38 kDa appeared. This antibody recognized weaker bands at 38-40 and 58-60 kDa in the soft epidermis. After reduction and carboxymethylation of proteins extracted from carapace and plastron, but not of proteins from the soft epidermis, protein bands at 15-17 and 35-37 kDa were found when using the anti-beta 1-keratin antibody. Loricrin-, filaggrin-, sciellin-, and transglutaminase-like immunostaining was detectable only in the transitional and lowermost corneous layers of the soft epidermis. Vesicular bodies in the transitional layer were immunolabeled by the anti-loricrin antibody, and weakly by the anti-filaggrin and anti-transglutaminase antibodies. In immunoblots, the anti-loricrin antibody reacted with a major band at 50-54 kDa in both carapace-plastron and soft epidermis. The anti-sciellin antibody detected major bands at 38-40 and 50 kDa in hard epidermis, and at 50 and 54-56 kDa in soft epidermis. Filaggrin-like immunostained bands were observed at 50-55 and 62-64 kDa. This immunostaining was probably due to a common epitope in filaggrin and some keratins. Histidine was evenly incorporated in the epidermis, and the ultrastructural study showed random labeling, often associated with keratin bundles of alpha and beta-keratinocytes. Histidine-labeled protein bands were not found in the carapace-plastron. In the soft epidermis, weakly labeled bands at 15-20, 25, and 45-60 kDa were found occasionally. The latter bands probably represented neo-synthesized keratins as was also indicated by the ultrastructural autoradiographic analysis. In conclusion, our study suggests that proteins with epitopes that they have in common with cornification proteins of mammalian epidermis are also present in the epidermis of turtle.