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Collective motion in biological matter

Collective motion in biological matter
Physics of active matter – Experiments performed at the National Institute of Information and Communications in Kobe, Japan, analyzed by scientists from Japan and France (CEA-Iramis, Saclay), allow to visualize and explain, at the scale of a living cell, the spontaneous emergence of large-scale structures in a population of moving biomolecules.

22 March 2012

What are the interactions at play when identical objects self-organize into an
ordered collective motion? This question arises in many situations, from the
molecular scale in living cells to the motion of large animal groups such as fish
schools.

In vitro experiments performed at the National Institute of Information and Communications in Kobe
(Japan), analyzed and modelled in collaboration with CEA-Iramis in Saclay, France,
show how basic components of living cells can self-organize their motion into large,
dynamic structures. These observations were obtained via the fluorescent marking
of the biomolecules involved.

The quality of this observation and of its analysis are reported in a
publication in Nature.

The Japanese researchers first prepared a « carpet » of molecular motors (dynein
proteins), which was flooded with a solution containing microtubules, which are
basic filaments involved in the structure of the cytoskeleton. In presence of ATP
(the chemical source of energy of most biological processes), the dynein heads
attach and collectively displace microtubules which then move steadily in two
dimensions.
If both the density of dynein motors and that of attached microtubules are high,
one observes, in a few minutes, the spectacular emergence of a lattice of vortices
with a typical diameter much larger than the microtubule length (400 μm vs 10
μm).

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The analysis of supplementary experiments together with a semi-quantitative
theoretical modeling have shown that the combination of only two elementary
features, the smooth and continuous motion of isolated microtubules and their
nematic alignment upon collision, is sufficient to explain the origin of this collective
organization into a vortex lattice.

This is the first time that scientists observe and explain clearly such a
phenomenon, from the elementary mechanisms at play to the large-scale
emergent structures.

Physics of « active matter » is the new field dealing with this
type of situations, where energy is spent locally to produce motion. Whereas one
cannot compare the biological function of the dynamic organization of living cells
with the ethological role of collective motion of large animal groups, theoretical
analysis is able to uncover deep similarities and use common analysis tools in all
cases.

The detailed observation of the organizational processes at play in the living cell
could give rise to applications. New biomaterials could for instance be created by
« freezing » the spontaneous dynamic structures reported here.

Large-scale vortex lattice emerging from collectively moving microtubules,
Yutaka Sumino, Ken H. Nagai, Yuji Shitaka, Dan Tanaka, Kenichi Yoshikawa, Hugues Chaté & Kazuhiro Oiwa. in Nature, 22 March 2012

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