Immunological characterization of a newly developed antibody for localization of a beta-keratin in turtle epidermis

Turtle scutes are made of hard (beta)-keratins. In order to study size and localization of beta-keratins in turtle shell, we produced a rat polyclonal antiserum against a turtle scute beta-keratin of 13-16kDa, which allowed the immunolocalization of the protein in the epidermis. In immunoblots the antiserum recognized turtle beta-keratins but showed variable cross-reactivity with lizard, snake, and avian beta-keratins. The turtle antiserum appears less cross-reactive than a chicken scale antiserum (Beta-1). In bidimensional immunoblots, three main protein spots at 15-16 kDa with pI at 7.3, 6.8, 6.4, and an unresolved large spot at 40-45 kDa with pI around 5 were more constantly obtained. The latter may result from the aggregation of the smaller beta-keratin protein. The corneous layer of the carapace and plastron of various species of chelonians appeared immunofluorescent. The ultrastructural immunolocalization showed sparse labeling over beta-keratin filaments of cells of the horny layer of both carapace and plastron. The study for the first time shows that the isolated protein band derived from a component of the beta-keratin filaments of the corneous layer of turtles. This antibody can be used for further studies on betakeratin expression and sequencing in chelonian shell. No labeling was present over other cell organelles or layers of turtle epidermis and it was absent in non-epidermal cells. The specificity for turtle beta-keratin suggests that the antiserum recognizes some epitope/s specific for chelonians beta-keratins, and that it also variably recognizes other reptilian and avian beta-keratins.