![]() Furthermore, the health of the hooves of farm and draft animals is of crucial economic importance to large animal producers and forms the basis of a longstanding interest in veterinary medicine concerning the structure and function of keratinized and cornified tissues. Keratin-rich tissues are studied for their economic importance in the wool industry, for cosmetics and dermatology ( Er Rafik et al. For example, the sheaths of horns have been fashioned into drinking vessels mammalian fur has been used for clothing the skin of reptiles has been manufactured into leather for clothing and pouches mammalian hair has been used to make felt or to spin yarn for weaving and knitting feathers have been used for various bedding materials and clothing baleen has been used as whalebone in the fashion industry ‘tortoise shell’ has been used for making combs and decorative objects and hooves of farm animals have been used as slowly decaying fertilizers ( Gupta & Ramnani, 2006 Thys & Brandelli, 2006). ![]() In order to understand the functions of intermediate filaments as components of the cytoskeleton for the cells to respond to extracellular forces ( Reichelt, 2007), to provide a network for organized processes of transportation and to participate in trans-membrane signaling processes, an integrated approach to keratins, filament formation and assembly of a cytoskeleton in connection with keratin filament-associated proteins (KFAPs), focal cell membrane modifications, and intercellular cementing substances is necessary.Ĭorneous, or horny, tissues have a long history of interest due to their economic, practical and emotional value. As an analogy, a review of collagen would also make sense only within the context of connective tissue structures ( Wang, 2006). When we started to survey, collect and organize the current knowledge on keratins (unless mentioned otherwise, hereafter the term ‘keratins’ refers to keratin proteins) and keratin filaments for the invited review of keratins in soft-keratinized epidermis and epithelia, we soon realized that such a study would lead to a greater understanding only if the keratins were discussed as integral elements of cells, tissues and organs. This review focuses on keratins and keratin filaments in mammalian tissue but keratins in the tissues of some other vertebrates are also considered. Future research in keratins will provide a better understanding of the processes of keratinization and cornification of stratified epithelia, including those of skin modifications, of the adaptability of epithelia in general, of skin diseases, and of the changes in structure and function of epithelia in the course of evolution. The processes of keratinization and cornification in skin modifications are different especially with respect to the keratins that are produced. It is currently understood that all stratified epithelia are keratinized and that some of these keratinized stratified epithelia cornify by forming a Stratum corneum. Recently, new functions of keratins and keratin filaments in cell signaling and intracellular vesicle transport have been discovered. At this point in time, the concepts of keratins and of keratinized or cornified epithelia need clarification and revision concerning the structure and function of keratin and keratin filaments in various epithelia of different species, as well as of keratin genes and their modifications, in view of recent research, such as the sequencing of keratin proteins and their genes, cell culture, transfection of epithelial cells, immunohistochemistry and immunoblotting. Similarly, the nomenclature of epithelia as cornified, keratinized or non-keratinized is based historically on the notion that only the epidermis of skin modifications such as horns, claws and hooves is cornified, that the non-modified epidermis is a keratinized stratified epithelium, and that all other stratified and non-stratified epithelia are non-keratinized epithelia. ![]() Currently, the term ‘keratin’ covers all intermediate filament-forming proteins with specific physicochemical properties and produced in any vertebrate epithelia. Keratins were then defined as certain filament-forming proteins with specific physicochemical properties and extracted from the cornified layer of the epidermis, whereas those filament-forming proteins that were extracted from the living layers of the epidermis were grouped as ‘prekeratins’ or ‘cytokeratins’. Subsequently, it was realized that this keratin is actually a mixture of keratins, keratin filament-associated proteins and other proteins, such as enzymes. Historically, the term ‘keratin’ stood for all of the proteins extracted from skin modifications, such as horns, claws and hooves. ![]()
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