Editorial overview: Cell architecture: Intermediate filaments — from molecules to patients
Résumé
From microbes to man for cells to have shape, form and function they need a dynamic, internal skeleton. This skeleton is known as the cytoskeleton which comprises three major filament systems: microfilaments, microtu-bules, and intermediate filaments. Whereas microfilaments and microtu-bules serve as tracks for motor proteins and are engaged in cell motility, intermediate filaments are fundamentally engaged in determining cellular plasticity. Intermediate filaments are crucial for the mechanical integrity and biological function of many different tissues in the body. In this issue of Current Opinion in Cell Biology, leaders from the field of intermediate filaments unravel the novel developments in biological, physical , and chemical technology which contribute to our recent increase in knowledge of the nanomechanics and biological function of the intermediate filament cytoskeleton. In sharp contrast with the components of the microtubule and the actin cytoskeleton which are more or less ubiquitously expressed in all cell types, the intermediate filament gene family comprises over 70 members which are introduced here by Peter and Stick. With the exception of the nuclear cytoskeleton formed by the ubiquitously expressed lamins, presented in the review of Gruenbaum and Medalia, intermediate filament proteins are differentially expressed during development and in distinct cell types. In addition, it has recently been shown that splice variants of intermediate filament proteins are expressed, adding a level of complexity to this system. The large variety of intermediate filament proteins form highly specialized polymeric filamentous networks, such as keratins in skin, vimentin in mesenchymal cells, neurofilaments, GFAP, a-internexin and synemin in the central nervous system, desmin and syncoilin in muscle, peripherin in the peripheral nervous system and nestin in neural stem cells. Reviews from Loschke et al., Hol and Pekny and Laser-Azogui et al. describe intermediate filament networks specifically found in epithelial, glial, and neuronal cells and highlight their structural and functional properties. Despite the broad variety of intermediate filament proteins expressed in different tissues, there is a high level of similarity in the structural design of the intermediate filament cytoskeleton. The review by Chernyatina et al. offers an overview of the structure of intermediate filament proteins. The monomers making up the filaments do differ in their amino acid sequence, but share similar protein domain motifs, as they all consist of a central a-helical rod flanked by flexible and highly variable N-termini and C-termini. All intermediate filament proteins form networks following a similar, hierarchical assembly scheme. Intermediate filaments have very attractive