31 May 1999

It's A Boy! First Male Mammal Cloned

Until now the elite club of clones has only consisted of females, such as Dolly the sheep and Cumulina the mouse. But now that club has gone equal opportunity, with researchers announcing the cloning of a male mouse.

"Fibro" is also the first documented, live mammal cloned from adult cells that do not originate in the reproductive system, which suggests that adult animals can be cloned from any of the body's cells.

Ryuzo Yanagimachi and Teruhiko Wakayama at the University of Hawaii say the technique is still tricky -- they only got one living mouse out of 274 tries -- but Fibro seems healthy and normal. Male animals have been cloned before, but only using fetal cells, which are much easier to clone because of their early stage of development.

It is much harder to clone animals from adult cells -- Dolly, some Japanese heifers and Cumulina, the cloned mouse presented to the world by Yanagimachi and Wakayama last year, are rare examples.

They were made using cells related to reproduction -- Dolly from the mammary gland cell of a ewe and Cumulina from so-called cumulus cells, which nurture developing eggs inside the ovaries.

So many scientists had believed that there might be something unique about females, or perhaps even female reproductive cells, that made them amenable to cloning.

Wakayama and Yanagimachi, writing in the journal Nature Genetics, said it is now clear this is not the case.

"Our results demonstrate that cloning using adult somatic cells is not restricted to female or reproductive cells," they wrote.

Using their "Honolulu technique," which differs slightly from the method that scientists in Scotland used to make Dolly, they created 274 mouse embryos using skin clipped from the tail of a male mouse and implanted them into surrogate mother mice.

"Only three of 274 transferred embryos reached full term," they wrote. "Three mice from tail-tip cells were born alive, all of them males with black eyes."

Two died but one lived to adulthood and was the same reddish-brown color as the mouse whose tail was clipped.

The experiment means it might be possible to store an animal's complete genome, its collection of genes, using a tail snip or other cell instead of having to freeze an embryo, the researchers said.

"Moreover, precious animals of either sex, for example endangered species and transgenic animals, can be propagated by cloning irrespective of their fertility status."

Much of the cloning research going on is part of commercial and scientific programs to create genetically engineered, or transgenic, animals. Mice are bred to carry human genes, for example, so that drugs can be tested on them.