POWERFUL magnets can affect the way cells divide, say researchers who have
used magnets to levitate frog embryos. The finding complicates plans to use
magnetism to study the effects of microgravity on living organisms on Earth, but
may also provide a new tool to study cell division.
One way to understand the effect gravity has on life is to study how
organisms behave in space. But some scientists, including James Valles and his
colleagues at Brown University in Providence, Rhode Island, hope the same
lessons can be learnt more cheaply on Earth by floating cells
or organisms in extremely powerful magnetic fields
(鈥淎nd God said . . .鈥�, 快猫短视频, 26 July 1997, p 42).
This is possible because nearly all living tissue is weakly repelled by magnetic fields.
Using field strengths up to half a million times greater than that created by
the Earth, Valles鈥檚 team levitated frog embryos to see how this would affect
their cell division. In a fertilised frog egg, the direction of the first three
cell cleavages normally occur relative to gravity鈥檚 orientation. The first
cleavage cuts it vertically in half. The second cut is also vertical, leaving
four segments. The final slice is horizontal, and cuts the four segments in
half.
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To their surprise, the researchers found that if the magnetic field was
applied parallel to the first two cleavages, the third division was also
vertical. But this wasn鈥檛 the result of microgravity. It happened even when the
embryo remained grounded in a magnetic field (Proceedings of the National
Academy of Science, vol 95, p 14 729). 鈥淪trong magnetic fields themselves
give this developmental effect,鈥� says Valles. 鈥淲e just didn鈥檛 expect that.鈥�
While this will make interpreting magnetic microgravity experiments more
difficult, it also suggests new uses for magnets in biology. Valles suspects the
third cleavage changes because long protein cables called microtubules, which
determine the direction of cleavage, are forced to orient themselves parallel to
the field. 鈥淢agnets could be an entirely new tool with which to manipulate that
process,鈥� Valles says.