Viable sperm were produced after seven months

Mice have been used to produce viable monkey sperm using tissue transplanted from the testes of macaques.

The US scientists involved say their work might one day help to conserve animals that are facing extinction.

It might also be possible to grow human sperm in mice, although the team agree this would be a controversial move.

The researchers, from the universities of Pennsylvania and California, report their studies in the latest issue of the journal Biology of Reproduction.

In 2002, the same team produced goat and pig sperm from mice. It was the first time that sperm had been produced outside the original animal.

Testis transplant

The latest procedure involves transplanting a tiny amount of testicular tissue from an immature rhesus macaque monkey under the skin of a lab mouse.

Ina Dobrinski, of the University of Pennsylvania, and colleagues transplanted the tissue into mice that had deficient immune systems, so that it would not be rejected.

"We started this work with primate testis after we had success with domestic animals," Professor Dobrinski told BBC News Online.

The sperm were injected into an egg...

After seven months, the testes grafts on the backs of the mice were seen to produce viable sperm.

Grafting immature testis tissue appears to work because the host mouse had been castrated, Dobrinski says.

This boosts levels of the brain hormones that switch on sperm production, so the young tissue grows rapidly. The technique is expected to work on adult testis grafts, too.

The Pennsylvania group will now try the procedure on testis tissue from domestic cats, as a trial for endangered big cats that rarely survive to reproductive age in captivity.

The technique could also produce offspring from other endangered species or valuable livestock, even if only immature males exist.

The latest work with primates will help reduce the number of such animals used in laboratories.

Of mice and men

"The main benefits we see are that this approach provides a system to study and manipulate primate spermatogenesis, thereby minimizing the need for experimentation in primates," Professor Dobrinski says.

...which resulted in an embryo

In theory, human testis tissue grafted on to mice could produce sperm.

The technique may also provide a way of testing toxins or male contraceptive drugs on sperm development.

Prepubescent boys undergoing treatment for cancer that will render them sterile could benefit, Professor Dobrinski suggest.

Their immature testis tissue could be removed prior to treatment and transplanted on to mice for sperm production.