Overview

The intermediate filaments are an essential component of the cytoskeleton. Presently six types of intermediate filament have been identified. Type I and II are acidic and basic keratin proteins. Type III is of mesodermal origin and comprises four proteins: vimentin, desmin, glial fibrillary acidic protein (GFAP), and peripherin. Vimentin is commonly found in mesenchymal cells, desmin in muscle cells, GFAP in astrocytes, while peripherin is found in peripheral nervous system neurons (PNS). Type IV consists of three neurofilaments; NF-Light, NF-Medium, NF-Heavy, and α-internexin, nestin, and synemin. Type V consists of nuclear lamins, and Type VI comprises newly discovered phakinin and filensin protein found in the lens cells and the neuronal stem cells.

Based on their location, these filaments are broadly classified into cytoplasmic and nuclear intermediate filaments. Type I, II, IV, and VI are exclusively cytoplasmic filaments. The cytoplasmic intermediate filaments are tissue-specific. Type III filaments are found in both cytoplasm and the nucleus, while Type V is restricted to the nucleus. Several diseases are related to gene mutation encoding the different types of intermediate filaments. Some important diseases related to intermediate filaments include epidermolysis simplex bullosa, pachyonychia congenita, Hutchinson-Gilford progeria, Charcot Marie Tooth disease, and acquired partial lipodystrophy.

Procedure

Intermediate filaments are of six types. The first four contribute to cytoplasmic architecture. Type five is found abundantly within the inner lining of the nuclear membrane, while the recently discovered type six is predominantly found in lens cells and neuronal stem cells.

Types one and two consist of interdependent keratin proteins and form heterodimeric filaments found primarily in epithelial cells. Both have high tensile strength, and are commonly found in tissues undergoing repeated wear and tear, such as nails and skin.

Type three consists of four proteins—vimentin, desmin, glial fibrillary acidic protein, and peripherin. They can form both homo and heterodimers.

Type four includes neurofilament or NF proteins, with glutamic acid-rich tails, and filaments with short sidearms, that provide axon structural support and determine axon diameter.

Type five consists of nuclear lamins having an immunoglobulin-fold with a CAAX box consisting of cysteine, two aliphatic amino acids, and another non-specific amino acid at its C-terminal.

Lastly, type six consists of beaded intermediate filaments that can either form homo or heterodimers with each other.