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We may have to abandon our dreams of colonising space
 
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 — at 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. "This shows gravity triggers the pattern," says Tabony.
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"Physicists insisted this research wasn’t worth doing, because gravity is too small, compared to electrostatic or thermal forces on molecules, to affect chemical reactions," says Didier Schmitt, head of life sciences at ESA’s European Space Technology and Research Centre in Noordwijk, the Netherlands. "This proves they were wrong."
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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. "Normally, the microtubules form long, straight fibres radiating towards the cell membrane," 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.
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The findings might explain some of the health problems people living in space have, such as depressed immune systems. "Over a long time, or for generations," says Tabony, "I suspect we wouldn’t do well at all."
 
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.
 
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Author: Debora MacKenzie, Brussels
 
New Scientist issue 15th July 2000
 
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