The different kinds of IFs share some basic characteristics: they are from 9 to 11 nm. in diameter and are very stable; their main function being a structural one. Different types of IFs are distinguished by the protein each is made of.
Lamin IFs
These form a network, the nuclear lamina, that supports the nuclear envelope. There are lamin A, B, and C filaments. Lamin A and C form the lamin network and are attached to the nuclear membrane by lamin B.
These proteins are the most diverse among IFs. The many isoforms are divided in two groups: "soft" keratins (cytokeratins) in epithelial cells (image to right), and "hard" keratins (hair keratins) wich make up hair, nails, horns and reptilian scales. Ragardless of the group, keratin can be acidic or basic. Acidic and basic keratins can bind each other to form acidic-basic heterodimers, these heterodimers can then associate to make a keratin filament.
Type III IFs
Desmin IFs are structural components of the sarcomeres in muscle cells.
Peripherin is a Class III intermediate filament subunit found in both the peripheral and central nervous systems, though it is concentrated, as its name suggests, in the neurons of peripheral ganglia and their processes.
Peripherin is also a major component of the cytoskeleton of PC12 cells, widely used model system for studies of neuronal differentiation.
Peripherin is not related to peripherin-RDS, a photoreceptor protein associated with retinal degeneration and blindness.
Peripherin, an intermediate filament of sympathetic neurones, is undetectable in chromaffin cells of GR mutants.
Peripherin, a neuronal intermediate protein, is stably expressed by neuroendocrine carcinomas of the skin, their xenograft on nude mice, and the corresponding primary cultures.
Peripherin immunoreactivity was specifically distributed in some small ganglion neurons and in their central and peripheral extensions, particularly in fibers reaching the lower part of the outer hair cells.
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