Fatherless mice created without sperm

Japanese and Korean scientists have created a fatherless mouse without using sperm in a reproductive feat akin to the birth of Dolly the sheep, the world's first cloned mammal.

Bees, ants, aphids and some fish and reptiles reproduce without having sex in a process called parthenogenesis. But creating a living mammal from same-sex parents was thought to be impossible. Until now. The birth of Kaguya, the daughter of two female mice, which is reported in the science journal Nature on Wednesday by Tomohiro Kono of Tokyo University of Agriculture, shows that a healthy mammal known as a parthenote can be created without any male help.

"The parthenote developed to adulthood with the ability to reproduce offspring," Kono and his colleagues said in the Nature report.

Mammals inherit one set of chromosomes from their mothers and another from their fathers. Embryos containing only female chromosomes usually die early in the womb and those with only male genetic material are abnormal.

Kono and his team overcame the problem and created Kaguya by fusing two female eggs after knocking out a key gene in the donor egg. The gene is involved in imprinting, a mechanism which controls the activity of genes inherited from the father and mother.

The fused eggs were chemically activated to produce embryos that were implanted into the wombs of mice.

"The paper shows that, like cloning, another asexual form of reproduction is possible in mice and may be possible in some other mammals," said Simon Best of the Biotechnology Industry Organisation.

"However, this was achieved with even lower efficiency than the cloning process used to make Dolly and therefore it is even more unacceptable and unsafe to consider using this for humans," he added.

Only 0.6 per cent of the embryos Kono and his colleagues created survived. It took hundreds of fused eggs to produce 28 offspring but Kaguya was the only mouse to survive. Others were stillborn or abnormal.

"This is an incredible achievement, the process of creating these mice required perseverance and patience: from around 600 eggs only two mice were created. As a result, this technique is far too complicated to be used in humans," said Professor Azim Surani of the University of Cambridge in England.

But the research could improve understanding of genetic imprinting and what causes abnormalities in embryos, as well as knowledge about the beginning of life.

Kono said his results suggest that paternal imprinting prevents parthenogenesis in mammals and ensures a male role in reproduction.

"Until we fully understand the role and regulation of imprinted genes in development, it seems that the participation of the father in reproduction will remain necessary," David Loebel and Patrick Tam, of the University of Sydney in Australia, said in a commentary in the journal.