Keratinization in the epidermis of amphibians and the lungfish: comparisonwith amniote keratinization

Keratinization in the epidermis of amphibians and the lungfish has been stu died by electron microscopy, autoradiography and immunocytochemistry to det ermine whether histidine-rich proteins, filaggrin and loricrin are present. In the lungfish and amphibian tadpoles, anti-keratin antibodies (AE1 and A E3) stain the whole epidermis but not the AE2 antibody, a marker for kerati nization. In adult epidermis, the AE2 antibody mainly stains keratinized la yers, AE1 mainly stained basal cells, less suprabasal cells: and no pre-ker atinized and keratinized layers, and AE3 stains all epidermal layers. This staining pattern resembles that of amniote epidermis. Little tritiated hist idine is taken up in toad epidermis at 4-6 h post-injection but 24 h after injection the radioactivity is most concentrated in the replacement layer b eneath the corneus. This indicates that protein synthesis takes place in th e epidermis but, due to the metabolic conversion that takes place in 24h, i t is unlikely that histidine-rich proteins are formed. Neither filaggrin-li ke nor loricrine-like immunoreactivities are present in amphibian and lungf ish epidermis. This indicates absence of histidine-rich matrix proteins and corneous cell envelope proteins and only mucus is present among keratin fi laments. Filaggrine-like and loricrin-like proteins are characteristic of a mniotes epidermis and might have originated in basic amniotes (cotylosaurs) . (C) 2001 Harcourt Publishers Ltd.