The cytoskeleton, pictured to the right, consists of:

• Microfilaments (5-7 nm in diameter)- composed of actin and regulate cell shape, contractility, cell motility, and cytokinesis.
• Microtubules (24 nm in diameter)- composed of tubulin dimers and contribute to cell polarity and provide tracks for organelle and chromosome movement.
• Intermediate filaments have diameters between those of microfilaments and microtubules (10-15 nm)- composed of a more diverse group of proteins and provide strength and support to cells.
  • Immunocytology to detect intermediate filament proteins is used clinically to aid in cancer diagnosis and treatment planning.Different cell types express unique intermediate filament proteins (e.g. epithelial cells express keratin intermediate filament proteins, some neural cells express glial fibrillary acidic protein, and muscle cells express desmin intermediate filament proteins). Staining to detect these filaments can help pathologists determine the origin of a tumor.

In routinely prepared H&E stained specimens, the cytoskeleton contributes to the eosinophilia of the cytoplasm. Immunocytology and fluorescence microscopy can be used to reveal beautiful arrays of microtubules (yellow) and microfilaments (purple).

The cytoskeleton, particularly the microfilaments and microtubules, are highly dynamic structures. Check out this live-imaging movie of a cell stained with antibodies to detect microtubules (green) and microfilaments (red). (Note, you will need a Flash plug-in to view this movie.) Notice the dynamic nature of the microfilaments and microtubules, which can be seen here undergoing continuous remodeling. In contrast, intermediate filaments are stable structures that do not undergo continuous rearrangement.

How about the nucleus?