Of men and mice

The first fertilisations of human eggs from rodent-reared sperm could come within the near future, says Dr Nikolaos Sofikitis of Tottori University in Yonago, Japan who took spermatogonia from infertile men and injected them into the testes of rats and mice.

In course of his research, Dr Sofikitis gave the injections to ten rats and eight mice. Five months later, he detected large numbers of mature human sperm in three rats and two mice. In one rat, he found fully motile sperm which, in fact, had 8220;better motility than that of many fertile men8221;, says a report published in New Scientist, a British sciencejournal.

According to reproductive experts, Dr Sofikitis8217;s technique would give researchers a powerful new tool to study the development of human sperm in animals instead of humans. That could speed up the development of male contraceptive drugs that prevent sperm from maturing, they say.

Fostered sperm could allow infertile men to father children through IVF. After failing in his initial attempts to breed spermatogonia from infertile men in the testes of mice, which rejected the spermatogonia due to their immune response, Dr Sofikitis tried again, this time injecting the sperms along with cells from recipient rodent8217;s eye.

Dr Sofikitis said cells-extracted from the fluid just in front of the rodent8217;s eye secrete a protein called fas ligand, a signalling molecule that triggers immune cells to commit suicide. This eliminated the last vestiges of an immune response in the mice and allowed its testes to take the human spermatogonia.

In his earlier research, Dr Sofikitis has fertilised hamsters eggswith hamster sperm fostered in rat8217;s testes and he expects the same should be possible for humans. However, according to fertility experts, sperm fertilised in this manner might run the risk of being genetically-damaged. The sperm could also carry disease if they become contaminated with rodent viruses, says Dolores Lamb, an andrologist at Baylor College of Medicine in Houston, Texas.

Nonetheless, all scientists agree that the technique is a major advance in medical science. 8220;If this guy8217;s done it, its great,8221; says Dr Roger Short, a reproductive biologist at the Royal Women8217;s Hospital in Melbourne.

Growing the sperm of one species in the testes of another has been a serious possibility since 1996, when Dr Ralph Brinster and his colleagues at the University of Pennsylvania in Philadelphia showed that the spermatogonia from rats could develop into mature sperm in the testes of a mouse. This led other researchers to suggest that human sperm might be cross-fertilised in the same way.

In this context, DrSofikitis8217;s technique could offer hope of fatherhood for many men.