Space

PREGNANT women and their fetuses are not severely affected by air travel - but the same may not be true for space travel. Zebrafish embryos raised in microgravity have been shown to develop cranial defects.

The changes are "not going to be a problem for the health of the organism - yet", says Tamara Franz-Odendaal, a developmental biologist at Mount Saint Vincent University in Halifax, Canada. She suspects the abnormalities are caused by changes in neural crest cells, which give rise to cranial cartilage and bone. With successive generations these effects could amplify, which doesn't bode well for extended human space voyages.

The research, presented last week at the Society for Integrative Biology conference in Salt Lake City, Utah, adds to growing evidence that reproduction and space just don't mix.

To mimic the weightlessness of space, Franz-Odendaal's graduate student Sara Edsall placed fertilised zebrafish eggs inside a bioreactor, which spins objects within it to create a microgravity environment. She began spinning the eggs 10 to 14 hours after fertilisation to coincide with a key stage in the development of cranial neural crest cells, and stopped them 12 to 96 hours later.

Once the fish had hatched, Edsall stained the cranial cartilage in half of them blue. She then compared these to fish that hadn't spent time in microgravity as embryos, and found that the branchial arches - bits of cartilage that support the gills and correspond to parts of the jaw in humans - appeared altered. To see if these problems persisted into adulthood, Edsall repeated the staining several months later on the second half of the group of fish. The adult fish were also abnormal: the bone at the base of their skull buckled, for example.

In 2002, Stephen Moorman, now at Robert Johnson Medical School in Piscataway, New Jersey, also found abnormalities in zebrafish eggs that had developed in microgravity. This time they were spun in a bioreactor 30 hours after fertilisation. Moorman found that the hatched fish developed deficits in their vestibular systems, responsible for balance (Developmental Dynamics, vol 223, p 285). The fish died after just two weeks.

Access to space missions is limited, so bioreactors allow researchers to conduct pseudo-space research here on Earth. Edsall hopes to carry out the zebrafish experiment in space in 2015.

The use of bioreactors is not without controversy, however. Kenneth Souza, a senior scientist at Dynamac Corporation which assists NASA, says bioreactors poorly mimic conditions in space, pointing out that medaka fish bred in space in 1995 showed no abnormalities. Edsall counters that the 1995 study did not have the same level of detail as hers, and so may have missed something.

What does seem clear is that space travel affects reproduction. Joseph Tash, a reproductive biologist at the University of Kansas Medical Center in Kansas City, examined 16 female mice that travelled aboard NASA's STS-131 mission last year. He found that the mice had shrunken ovaries, dying ovarian follicles and down-regulated oestrogen genes. Their reproductive systems "had shut down", he says.

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