Floating Fertility

Although his results may explain why sperm move faster in space, they don't necessarily imply that fertilisation will be easier. After all, if one enzyme (protein phosphatase) isn't activated properly perhaps others will be affected, too. Many enzyme reactions play a role in the fertilisation process: for example, to ready the sperm to insert the DNA into the egg. Says Tash: if enzyme processes are being altered by gravity - and they are - you can't even guess at the effect on fertilisation until you've studied more than just sperm movement.

Tash conducted his initial research using the European Space Agency's Biorack Facility on board shuttle missions STS-81 and STS-84. "Those were part of the MIR docking flights," he explains, "and there was no room for microscopes. Although we wanted to, we could not actually look at the sperm motility itself." As it turned out, doing without microscopes led to unexpected benefits. They were forced to concentrate instead on the proteins that are connected with the process. "As a result," says Tash, "we were able to identify [previously-unknown] proteins in the sperm tail that are very tightly coupled to the initiation of sperm movement."

In 1997 Space Shuttle Atlantis carried sperm from sea urchins into space for Tash's experiments.

More recently, Tash has studied the effects on sperm of hypergravity (greater than normal gravity). Working with a centrifuging microscope in Germany, he was able to examine activated sea urchin sperm under conditions up to 5 G (five times normal Earth gravity). His findings expanded on the results of the shuttle experiments.

On the shuttle, Tash explained, researchers examined the proteins by activating millions of immotile sperm and then, using antibodies, looking at the way the proteins had changed 30 and 60 seconds later. With the centrifuging microscope, "we were actually taking measurements of individual sperm cells." Following each of the unique wrigglings of hundreds of individual sperm, Tash found that sperm motility begins to deteriorate at as little as 1.3 Gs. And, he found, in hypergravity fertilisation itself is reduced by a full 50%. As in microgravity these effects seem to be driven by changes in phosphorylation.