Cytoskeletal proteins connecting intermediate filaments to cytoplasmic andnuclear periphery

Intermediate filaments (IFs), together with microtubules and microfilaments build up the cytoskeleton of most eukaryotic cells. Cytoplasmic Ifs form a dense filament network radiating from the nucleus and extending to the pla sma membrane. The association between the cytoplasmic and nuclear surfaces appears to provide a continuous link important for the organisation of the cytoplasm, for cellular communication, and possibly for the transport into and out of the nucleus. Cytoplasmic Ifs approach the nuclear surface, thin fibrils seem to connect the Ifs with the nuclear pore complexes and a direc t interaction of cytoplasmic Ifs with the nuclear lamin B has been observed by in vitro binding studies. However, none of the components that cross-li nk Ifs to the nucleus has been unambiguously identified. Furthermore, if a direct interaction between cytoplasmic Ifs and the nuclear lamin B occurs i n vivo, the question of how cytoplasmic Ifs get access to the nuclear inter ior remains to be resolved. The association of Ifs with the plasma membrane s involves different components, some of which are cell type specific. Two specialised complexes in epithelial cells: the desmosome and the hemidesmos ome, serve as attachment sites for keratin filaments. Desmoplakin is consid ered as the cross-linking component of Ifs to the desmosomal plaque, wherea s BPAG1 (bullous pemphigoid antigen) would cross-link Ifs at the hemidesmos omal plaque. In other cell types the modality of how Ifs are anchored to th e plasma membrane is less well understood. It involves different components such as the spectrin based membrane skeleton, ankyrin, myosin, plectin and certainly many other still unravelled partners. Association between the If s and cellular membranes plays an important role in determining cell shape and tissue integrity. Thus, the identification and characterisation of the components involved in these interactions will be crucial for understanding the function of intermediate filaments.