Description:
<jats:title>Abstract</jats:title><jats:p>Using specific anti‐β keratin and general anti‐α keratin antibodies, keratins were located in the epidermis of the alligator during the final developmental stages by ultrastructural and immunocytochemical methods. The maturation of the bilayered periderm (= embryonic epidermis) coincides with the disappearance of cell organelles, including the 25–35‐nm‐thick coarse filaments, and the coalescing of α‐keratin filaments into a compact mass. The plasmalemma of peridermal cells forms a 15–25‐nm‐thick electron‐dense corneous envelope. These changes start at stage 25, about 3 weeks before hatching, and continue until hatching when the embryonic epidermis is shed. Immature β‐keratogenic cells beneath the embryonic epidermis accumulate immunolabelled β‐filaments which are packed into thin, electron‐pale β‐keratogenic cells in the corneous layer. Together, electron‐pale and electron‐dense materials form a compact 3–4‐nm filament pattern of β‐keratin. Melanosomes from epidermal melanocytes, incorporated into β‐cells, give rise to the banded skin pattern of hatchlings. β‐keratin production is much reduced in the hinge regions, where many α‐filaments remain packed together with lipid droplets or mucous granules into thinner, more electron‐dense, α‐cells. The keratinaceous material of the α‐cells is mostly concentrated along the cell membrane, while the lipid/mucous material remains centrally located, as in sebokeratinocytes of the apteric areas of avian skin. Some lipid and mucus is also incorporated into typical β‐cells of the outer scale surface, so that lipids are part of the fully keratinized hard keratin layer of the alligator. Lipids within β‐cells of outer scale surfaces and α‐cells of the hinge region are probably responsible for limiting water loss and ion movements across the skin. Neither typical mammalian keratohyalin granules nor lepidosaurian keratohyalin‐like granules were detected anywhere in alligator epidermis. The combination of anti‐β and anti‐α keratin antibodies revealed different distributions of β‐ and α‐keratins. In late embryonic stages (25–26 to hatching), β‐keratin occurs only in the upper suprabasal cells, in prekeratinized and keratinized layers, whereas α‐keratin bundles (tonofilaments) remain only in the lowest layers. The cross‐reactivity of the β‐antibody, produced against a chick scale keratin, further shows that avian and crocodilian hard (β) keratins share common antigenic sites, reflecting a phylogenetic affinity between these taxa.</jats:p>