The fascinating dances of microtubules, both skeletons of our cells and highways for molecules

“No one had ever seen this. We didn’t believe it ourselves. “ Here is what two French teams said to each other, without prior consultation, after the discovery of surprising phenomena at the heart of cell life.

The two groups are studying the same object with puzzling properties: microtubules. These are long tubes (tens of micrometers) thin (25 nanometers in diameter), small “spaghetti” which act as a skeleton for the cells, but also highways for the transport of various molecules within them. All in constant agitation, made up of movements, creations, destruction … The best known of these tubes guide nerve signals along the axons of neurons or else cause numerous cilia or flagella to oscillate, like those of the tail of spermatozoa.

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The first team (Institut Curie, Cochin Hospital, Max-Planck Institute in Dresden and University of Bonn, Germany) took an interest in this beating appendage, of which a malfunction of the machinery is the cause of infertility.

Analogue au paquito

A flagellum moves and waves, thanks to the microtubules, which themselves oscillate thanks to a technique analogous to the Basque sport of paquito, where the participants sitting in single file make one of their team members advance, lying on their raised arms. It takes strength and synchronization. Ditto for the flagellum. Molecular motors, called dyneins, have one end hooked tightly to a first layer of microtubules, while their other ends, the “arms”, can catch or break off with a second layer of microtubules around the first. By pushing and pulling regularly, the assembly of dyneins undulates the upper and creates the flutter of the tail of the sperm, which thus runs straight towards the eggs.

Unless the microtubules are very slightly disturbed, as the researchers explain to the “one” of Science January 8. By genetically modifying mice, they prevented the arrival of only a few sweet amino acids, glycines, on the surface of microtubules, without interfering with the life of mammals. “We almost gave up because this change seemed to have no effect. Even the sperm appeared to be normal ”, recalls Carsten Janke, research director at CNRS and head of this team. By better studying the behavior of gametes, they nevertheless discovered that some no longer move in a straight line but go in circles. “We had to dive down to the molecular level to understand how a modification, a priori non-essential, could have such physiological consequences”, explains Carsten Janke.

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The fascinating dances of microtubules, both skeletons of our cells and highways for molecules