What is Cytoskeleton?
Cytoskeleton refers to the network of protein fibers in the eukaryotic cytoplasm. It includes both narrow and broad, concepts. The broad cytoskeleton includes nuclear skeleton, cytoplasmic skeleton, membrane skeleton and extracellular matrix skeleton., in a narrow sense refers to the cytoplasmic skeleton, including microfilaments (MF), microtubules (MT) and intermediate filaments (IF).
Table 1. Comparison of microfilaments, microtubules and intermediate filaments
|
Cytoskeleton
type
|
Diameter(nm)
|
Structure
|
Subunit examples
|
|
Microfilaments
|
6
|
Double helix
|
Actin
|
|
Microtubules
|
23
|
Protofilaments, in turn consisting of tubulin subunits in complex with stathmin
|
α- and β-Tubulin
|
|
Intermediate
filaments
|
10
|
Two anti-parallel helices/dimers, forming tetramers
|
Vimentin (mesenchyme)
Glial fibrillary acidic protein (glial cells)
Neurofilament proteins (neuronal processes)
Keratins (epithelial cells)
Nuclear lamins
|
The Function of Cytoskeleton
The cytoskeleton extends throughout the cell's cytoplasm and directs a number of important functions.
(1) It helps the cell maintain its shape and gives support to the cell.
(2) A variety of cellular organelles are held in place by the cytoskeleton.
(3) It assists in the formation of vacuoles.
(4) The cytoskeleton is not a static structure but is able to disassemble and reassemble its parts in order to enable internal and overall cell mobility. Types of intracellular movement supported by the cytoskeleton include the transportation of vesicles into and out of a cell, chromosome manipulation during mitosis and meiosis, and organelle migration.
(5) The cytoskeleton makes cell migration possible as cell motility is needed for tissue construction and repair, cytokinesis (the division of the cytoplasm) in the formation of daughter cells, and in immune cell responses to germs.
(6) The cytoskeleton assists in the transportation of communication signals between cells.
(7) It forms cellular appendage-like protrusions, such as cilia and flagella, in some cells.
Fig.1 Cytoskeleton (Figure from DR GOPAL MURTI/Getty Images)
Cytoskeleton and Human Health
The abnormal cytoskeletal system often occurs in cells under pathological conditions. For example, in patients with Alzheimer's disease, a large number of distorted microtubules and damaged intermediate filaments are found in the brain neurons. In malignant transformation cells, microtubules are often reduced and depolymerized, and abnormal cytoskeletons can enhance the motor capacity of cancer cells. The distribution of intermediate filaments is strictly tissue-specific, and most tumor cells still exhibit the intermediate filament type of the primary tumor after metastasis has occurred, so it can be used as a criterion for the differential diagnosis of clinical tumors and whether tumor cells are metastatic.
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