Floating Fertility

Researchers have found that gravity - either too much or too little of it - affects the behaviour of sperm in puzzling ways.

Things are different in space.

Humans sleep upside down. Hot air doesn't rise. Boiling water doesn't froth. Bones weaken, muscles atrophy, and an ordinary sneeze can send you flying! The list goes on and on....

Now scientists have added one more item - a surprising and important one - to the list of things that work oddly when the familiar feel of gravity vanishes:

Sperm.

According to Joseph Tash, a NASA-supported physiologist at the University of Kansas Medical Centre, sperm behave differently in the near-weightless environment of space than they do on Earth. Whether these changes will impair or aid fertility, he doesn't yet know. But, says Tash, it's becoming increasingly clear that in outer space, fertilisation - of humans, of animals, and even of plants - will very likely be affected.

The puzzling behaviour of space-faring sperm first attracted attention in 1988 when the German researcher U. Engelmann sent samples of bull sperm into orbit aboard a European Space Agency rocket. His goal, in that and a later experiment, was merely to determine whether changes in gravity affected the motility (movement) of sperm. He found that it did. The tiny cells appeared to move better in a low gravity environment - good news, it seemed, for fertilisation, which is closely tied to sperm motility. Perhaps making babies would actually be easier in space!

But, says Tash, who has studied the sperm of sea urchins on board NASA shuttle flights, it's not so simple.

Sperm movement, he explains, begins with a process called phosphorylation - a chemical reaction widely used by cells to control their own activities. In phosphorylation, an enzyme changes the functioning of a protein within a cell. This sets off a kind of domino chain reaction that starts some type of activity - like causing the tails of sperm to move, and to propel the sperm cell forward. On Earth, the tail movement is halted or modified when a second enzyme, known as a protein phosphatase, kicks in.

Image Credit. Dr. J. Tash. University of Kansas Medical Centre The behaviour of sperm - a basic biological process - is affected by gravity.

In microgravity, Tash found that the second enzymes don't do their job within the normal time period.