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The center of the cell: A cytoskeleton factory

​​We highlight a new role for the centrosome, cent​ral organelle of the cell attached to its nucleus: the assembly of actin filaments, cytoskeletal elements, cell skeleton. The centrosome was previously known for his involvement in the assembly of another element of the cytoskeleton: the microtubules. This discovery is described in Nature Cell Biology 14 December 2015.

Published on 15 December 2015
The supporting structure of cells, called cytoskeleton, is composed of several types of filaments. The main two types are actin filaments and microtubules. The former are short, flexible and cover the cell membrane, allowing them to change shape and move. The latter, long and rigid, form a star radiating out from the centrosome at the center of the cell. Microtubules act as rails for molecular engines in the transport of protein from one end of the cell to the other. The star-like structure of their network allows for the integration of information from the cell periphery to its center. In a recent study, a team of researchers has shown that the centrosome can directly promote actin-filament assembly—a confirmation that the two largest networks in the cytoskeleton meet at the center of the cell.

Scheme of a cell and its skeleton.
Actin filaments are in green. The microtubules appear in red, the cell nucleus is blue and the centrosome in green.
© Manuel Théry, CEA.

Actin filaments and microtubules are already known to interact physically and biochemically at the periphery of the cell. The growth of microtubules affects the contraction and assembly of actin filaments, and vice versa. In this study, the researchers have highlighed a new interaction between the two networks at the center of the cell. In a series of in-depth observations, the scientists were able to identify a network of actin filaments related to the centrosome. They also provided evidence for specific proteins involved in the production of these filaments.

The researchers purified centrosomes to complete their observations. The cell membranes were dissolved so as to recover all internal components and to extract the centrosomes. Once deposited on glass slides in the presence of tubulin monomers (components of microtubules), they were able to induce their growth. To the researchers’ great surprise, they observed that while in the presence of actin monomers, the tubulin monomers were actually capable of inducing the growth of filaments. This in vitro analysis outside of the cells clearly demonstrates the capacity of centrosomes to induce the assembly of both types of networks.

There is still a lot to learn about the specific role of these actin filaments in relation to the centrosome. Future results are expected to deeply impact the understanding of the cell's fundamental mechanisms (such as intracellular transport) and how these mechanisms adjust to the cell's movements and mechanics.​

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