Microtubules play a decisive role in the management of the internal organization of living cells. They serve as rails for intracellular transport and as cables to separate chromosomes during cell division. They are very dynamic polymers that are permanently assembled and disassembled at their ends. This process, called dynamic instability, allows the network of microtubules to produce forces and adapt its architecture to that of the cell.
Microtubules are composed of 13 proto-filaments that combine to form a rigid and hollow tube. But this arrangement is not as perfect as it seems. Recently, several laboratories have observed that the dynamics of microtubules are not limited to their ends. Indeed, tubulin molecules (the basic brick used for their polymerization) could also be added along a microtubule of constant length. But the underlying mechanism was still unknown.
To solve this question, a consortium of researchers at IRIG, the Institute of Genetics & Development of Rennes, the Cell Biology Research Centre of Montpellier and the Interdisciplinary Laboratory of Physics of Grenoble explored the possible links between the structure, biochemistry and incorporation of tubulin along microtubules. Their observations of microtubules in electron microscopy revealed the existence of many defects (holes, dislocations) along the few millimeters of microtubule present in each cell. Fluorescence microscopy analysis of the renewal dynamics of the molecules that make up the microtubules revealed that these nanoscopic defects in the wall of the microtubule are at the origin of the incorporation of new tubulin molecules.
These results show that, in microtubules as well as in metal alloys, structural defects can also be at the origin of original properties and thus offer a new lever to regulate their stability.
The structure of microtubules is dynamic in the vicinity of a defect. The incorporation of new tubulin molecules(yellow) into the network spreads the defect along the microtubule and effectively renews its composition. Illustration of
Illuscientia
Microtubules are rigid filaments that are part of the skeleton of cells. They are in permanent renewal and their average life time does not exceed a few minutes. Indeed, microtubules grow regularly, from the center of the cell to the periphery, but can at any time disassemble completely and randomly. The permanent reconstruction process allows the network of microtubules to adapt its architecture and to accompany morphological changes in the cells.