	University of Texas Medical Branch
	Cell Biology Graduate Program

Intermediate filaments

Intermediate filaments, also called "thick filaments" are important components of the cell's cytoskeletal system. They may stabilize organelles, like the nucleus, or they may be involved in specialized junctions. They are distinguished from "thin filaments" by their size (8-10 nm) and the fact that thin filaments are motile.

There are five major types, each unique to a particular cell type:

Keratin: Found in skin, produced by epidermal cells and completely fills upper cell layers of the epidermis.
Vimentin: Found in fibroblasts; used as a cytochemical marker for fibroblasts in tissue culture
Glial fibrillary acidic protein: GFAP is found in glial cells and is also used as a marker for this cell type.
Desmin: An intermediate filament marker for muscle cells
Neurofilament proteins: A marker for Nerve cells

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Each intermediate filament consists of an alpha helical rod domain which connects the amino (head) and carboxyl (tail) teminals. The rods coil around another filament like a rope to form a dimer. See Figures 16-13 and 16-14 in your text. These dimers then form staggered tetramers that line up head-tail. The final 10 nm filament is a helical array of these tetramers.

Cytoskeletal elements contribute to Cell Junctions which include the Zonula adherans, and the Desmosome (macula adherans). These are discussed in the lecture on membranes and in a later lecture on junctions.

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University of Texas Medical Branch

Cell Biology Graduate Program

Intermediate filaments