A tale of mice and men offer hope for infertile

Ever heard of the "yuk" factor? It's a measure that scientists use unofficially to gauge public reaction to work they're planning. Dolly the sheep? Muted yuk. Richard Seed wanting to clone humans? Big YUK.

So how about this: laboratory mice which make human sperm.

Yes, that was a predictable reaction. Relax: they're not here yet. But they are part of a serious idea which a serious scientist, Roger Short at the Royal Women's Hospital in Melbourne, plans to turn into reality in about a year or so.

Dr Short has already won ethical approval for the work from his local animal research committee, and has applied for funding from the US National Institutes of Health. His idea is to build on some earlier work by a scientist using rats and mice, and to transplant the germ cells from human testes into those of laboratory mice to investigate how, and how well, they develop.

The result might give clues into infertility treatment for men, as well as helping the development of male contraceptives which act only on the sperm, rather than on the whole body. In both arms of the research, the use of an animal model rather than lawsuit-prone humans could simplify developments that otherwise would take years. Testing male contraceptive drugs can be a risky business, since if the contraception is permanent, the drug company faces a damages claim from the would-be father.

Infertile men are often unable to produce sufficient sperm, usually due to a genetic fault in the Sertoli cells that nurture developing sperm. But a 1996 paper by a team at the University of Pennsylvania in the United States showed that rat germ cells injected into the testes of mice with disabled immune systems (so that their bodies do not attack the foreign cells) could mature into rat sperm.

New Scientist magazine reports today that Dr Short intends to repeat those experiments, and to see whether the sperm produced can fertilise a rat egg. He then aims to transplant human cells. It could take up to 18 months for his work to show results. There are, however, concerns that human sperm developed in a mouse testis might undergo changes which would produce congenital effects. The sperm might also be infected by viruses which are part of the mouse DNA - so-called retroviruses, whose presence in pigs has held up the prospect of organ transplants from genetically engineered pigs to humans.

However, David Shapiro, former head of the Nuffield Council for Bioethics, commented that some researchers might be tempted to rush ahead even so in the current climate. "There's this gung-ho attitude of let's have a go," he said.

New Scientist commented, "Even [Aldous] Huxley [who wrote Brave New World] might have squirmed at the idea of surrogate testicles." But it added that "The history of fertility research is dominated by wild ideas that have become clinical practice."

Don't forget, after all, that in vitro fertilisation - alias test-tube babies - was once heralded as the dawn of a brave new world. Somehow, though, people still seem to enjoy the old techniques. Perhaps it's something like the opposite of the "yuk" factor. Perhaps the "yum" factor?

- Charles Arthur, Science Editor