Intermediate filaments (IFs) are
cytoskeletal components found in the cells of many
animal species. They are composed of a family of related
proteins sharing common structural and sequence features. Intermediate filaments have an average diameter of 10
nanometers, which is between that of 7 nm
actin (
microfilaments), and that of 25 nm
microtubules, and they were initially designated 'intermediate' because their average diameter is between those of narrower
microfilaments (actin) and wider
myosin filaments found in muscle cells. Most types of intermediate filaments are
cytoplasmic, but one type, the lamins, are nuclear.