Cornification in reptilian epidermis occurs through the deposition of keratin-associated beta-proteins (beta-keratins) onto a scaffold of intermediate filament keratins.
The isolation of genes for alpha-keratins and keratin-associated beta-proteins (formerly beta-keratins) has allowed the production of epitope-specific antibodies for localizing these proteins during the process of cornification epidermis of reptilian sauropsids. The antibodies are directed toward proteins in the alpha-keratin range (40-70 kDa) or beta-protein range (10-30 kDa) of most reptilian sauropsids. The ultrastructural immunogold study shows the localization of acidic alpha-proteins in suprabasal and precorneous epidermal layers in lizard, snake, tuatara, crocodile, and turtle while keratin-associated beta-proteins are localized in precorneous and corneous layers. This late activation of the synthesis of keratin-associated beta-proteins is typical for keratin-associated and corneous proteins in mammalian epidermis (involucrin, filaggrin, loricrin) or hair (tyrosine-rich or sulfur-rich proteins). In turtles and crocodilians epidermis, keratin-associated beta-proteins are synthesized in upper spinosus and precorneous layers and accumulate in the corneous layer. The complex stratification of lepidosaurian epidermis derives from the deposition of specific glycine-rich versus cysteine-glycine-rich keratin-associated beta-proteins in cells sequentially produced from the basal layer and not from the alternation of beta- with alpha-keratins. The process gives rise to Oberhäutchen, beta-, mesos-, and alpha-layers during the shedding cycle of lizards and snakes. Differently from fish, amphibian, and mammalian keratin-associated proteins (KAPs) of the epidermis, the keratin-associated beta-proteins of sauropsids are capable to form filaments of 3-4 nm which give rise to an X-ray beta-pattern as a consequence of the presence of a beta-pleated central region of high homology, which seems to be absent in KAPs of the other vertebrates.
Comparative Histolab and Department of Biology, University of Bologna, Italy. lorenzo.alibardi@unibo.it
Lorenzo
L
Alibardi
D000818:Animals; D004817:Epidermis / Q000737:chemistry / Q000254:growth & development / Q000648:ultrastructure*; D018604:Epitope Mapping; D005455:Fluorescent Antibody Technique; D007150:Immunohistochemistry; D007382:Intermediate Filaments / Q000648:ultrastructure*; D007633:Keratins / Q000648:ultrastructure; D012104:Reptiles / Q000145:classification; D013045:Species Specificity; D053800:beta-Keratins / Q000032:analysis / Q000737:chemistry / Q000648:ultrastructure*
D053800:beta-Keratins; D007633:Keratins