THE skeletons within living cells may not form properly in zero gravity, say
researchers in France. This could dent human ambitions to live in space鈥攁t
least without artificial gravity. Their work also proves that, contrary to
received wisdom, gravity can influence chemical reactions.
Most cells have cytoskeletons of microtubules, which are fibres made of the
protein tubulin. James Tabony and his colleagues at the French Atomic Energy
Commission lab in Grenoble found that when cold solutions of mammalian tubulin
and the energy-releasing compound GTP are warmed to body temperature for six
minutes, microtubules form in distinct bands.
What is striking is that the bands form at right angles to gravity or, if
spun, to the centrifugal force. To prove gravity is responsible, the team sent
up tubulin on a European Space Agency (ESA) rocket, which exposed its payload to
13 minutes of weightlessness. Some tubulin experienced only microgravity while
being warmed for the critical six minutes, but other samples were spun in a
centrifuge. The spinning microtubules formed bands as usual, but those that
experienced only microgravity pointed in all directions. 鈥淭his shows gravity
triggers the pattern,鈥� says Tabony.
Advertisement
鈥淧hysicists insisted this research wasn鈥檛 worth doing, because gravity is too
small, compared to electrostatic or thermal forces on molecules, to affect
chemical reactions,鈥� says Didier Schmitt, head of life sciences at ESA鈥檚
European Space Technology and Research Centre in Noordwijk, the Netherlands.
鈥淭his proves they were wrong.鈥�
Work by Marian Lewis of the University of Alabama at Huntsville suggests that
gravity may also help orient microtubules inside living cells. She has flown
human white blood cells on board the space shuttle. 鈥淣ormally, the microtubules
form long, straight fibres radiating towards the cell membrane,鈥� Lewis says. But
after a day in orbit, the microtubules were going in random directions, she
says. However, it is not yet clear whether microgravity or the vibrations during
takeoff are to blame.
The findings might explain some of the health problems people living in space
have, such as depressed immune systems. 鈥淥ver a long time, or for generations,鈥�
says Tabony, 鈥淚 suspect we wouldn鈥檛 do well at all.鈥�
Tabony says the formation of the microtubule bands is also the first
experimental model of biological self-organisation, in which chemical reactions
spontaneously generate patterns in response to tiny asymmetries in the
environment. This was predicted by Alan Turing in the early 1950s, and later by
biophysicist Ilya Prigogine, a Nobel prizewinner.