<P> Microfilaments are composed of linear polymers of G - actin proteins, and generate force when the growing (plus) end of the filament pushes against a barrier, such as the cell membrane . They also act as tracks for the movement of myosin molecules that affix to the microfilament and "walk" along them . Myosin motoring along F - actin filaments generates contractile forces in so - called actomyosin fibers, both in muscle as well as most non-muscle cell types . Actin structures are controlled by the Rho family of small GTP - binding proteins such as Rho itself for contractile acto - myosin filaments ("stress fibers"), Rac for lamellipodia and Cdc42 for filopodia . </P> <P> Intermediate filaments are a part of the cytoskeleton of many eukaryotic cells . These filaments, averaging 10 nanometers in diameter, are more stable (strongly bound) than actin filaments, and heterogeneous constituents of the cytoskeleton . Like actin filaments, they function in the maintenance of cell - shape by bearing tension (microtubules, by contrast, resist compression but can also bear tension during mitosis and during the positioning of the centrosome). Intermediate filaments organize the internal tridimensional structure of the cell, anchoring organelles and serving as structural components of the nuclear lamina . They also participate in some cell - cell and cell - matrix junctions . Nuclear lamina exist in all animals and all tissues . Some animals like the fruit fly do not have any cytoplasmic intermediate filaments . In those animals that express cytoplasmic intermediate filaments, these are tissue specific . </P> <P> Different intermediate filaments are: </P> <Ul> <Li> made of vimentins . Vimentin intermediate filaments are in general present in mesenchymal cells . </Li> <Li> made of keratin . Keratin is present in general in epithelial cells . </Li> <Li> neurofilaments of neural cells . </Li> <Li> made of lamin, giving structural support to the nuclear envelope . </Li> <Li> made of desmin, play an important role in structural and mechanical support of muscle cells . </Li> </Ul>

Cytoskeleton is involved in which of the following