Present in nearly all animals, but absent from plants and fungi Rope-like network of filaments in the cell Principle function is maintenance of cell structure - provide tensile strength to the cell

I.F.s do not have a defined polarity (I.e. no plus or minus ends) I.F.s have no associated motor proteins I.F.s do not bind to nucleotides (ATP or GTP) I.F.s are very stable compared to actin or microtubules

Cancer cells - lose the characteristic shape of the parent tissue I.F. gene expression is often unaffected Identification of I.F. proteins in tumor biopsies using antibodies can pinpoint origin of tumors (I.e. neurofilaments in metastatic cells from brain cancers) Physicians tailor treatment to particular types of cancer

Stem cells in the interior Dead cells at outermost surface Keratin remains - hard, waterproof, resists abraisions Makes up hair, nails, skin, & feathers

attachment membranes Desmosomes are formed in specialized areas of cells - the cytoplasmic side contains tonofibrils that are anchored in a plaque of proteins. Cadherin molecules provide the cell - cell interactions.

Hemidesmosomes connect epithelial cells to the basal lamina. The integrin binds to proteins in the plaques and to laminin in the extracellular matrix.

Endothelial transmigration - white blood cells leave the bloodstream to combat infection Process is impaired in vimentin mutant mice

Desmin filaments are tethered to the Z disk and evelope the sarcomere Dont participate in contraction, but maintain structural integrity Mutant mice have misaligned muscle fibers Mutations in human desmin causes muscle disorders

Unlike other I.F.s, they have side arms that project from the core filament Fill and pack the cytoplasm of neurons Neurons in KO mice make axons with smaller diameters Charcot-Marie-Tooth disease: neuropathy where PNS degenerates

Nuclear lamins form a basket-like structure on inner side of nuclear membrane Protects structure of nucleus

Microtubule (red), vimentin (orange), plectin cross-linker (blue)