Experiment of mice - and no men: FUSING CHROMOSOMES PRODUCES OFFSPRING

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FUSING CHROMOSOMES PRODUCES OFFSPRING

Experiment of mice - and no men

 

 

http://www.newsday.com/news/health/ny-hsmice223768233apr22,0,4936959.story?c

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BY ROBERT COOKE

SPECIAL CORRESPONDENT

 

April 22, 2004

 

 

Males may feel less useful now that Japanese researchers have created the

first mammals - mice - via virgin birth.

 

By forcing the chromosomes of two females to mesh inside a single egg, the

scientists found they could produce viable offspring, one of which survived

into adulthood. Papa, alas, was left out of the loop entirely.

 

 

 

 

 

 

 

 

 

 

 

The milestone was announced in today's issue of the journal Nature. All

offspring were female because no male Y chromosome was involved.

 

Led by Tomohiro Kono at the Tokyo University of Agriculture, the nine

researchers constructed hundreds of mouse eggs containing only the

chromosomes from two females. The manipulated eggs were implanted into

surrogate mothers, and from these they obtained two female mice. One matured

into an adult of normal size and weight. She was named Kaguya after a

Japanese fairy-tale character, and produced pups of her own via normal

mating.

 

" It is a fascinating and very credible report, " said Dr. Arthur Beaudet,

chairman of molecular and human genetics at Baylor College of Medicine in

Houston. But " I don't see it as something that would have a serious

likelihood of happening naturally. And I certainly do not see it as

something that should be tried in humans. "

 

Reproduction sans Dad is called parthenogenesis and is seen in many species,

including snakes and birds, but not in mammals. In mouse experiments,

parthenogenic embryos die by day 10 of gestation.

 

Kono and colleagues got around that by using two half-sets of female genes,

called haploid sets. One special haploid set contained mutations that kept

it from acting female. Its genes functioned as though they'd come from a

male. To the researchers' surprise, only two genes - H-19 and Igf-2 - were

involved in controlling the imprinting process. This mechanism is a

mysterious alternative means of gene control. Both mother and father try to

control how genes are used through imprinting, which alters what genes do

without causing genetic damage.

 

The imprinting process has been a biological puzzle for decades, and the

spermless births in Japan may help resolve it.

 

According to animal reproduction physiologist George Seidel at Colorado

State University, theoretically " there is no good reason why

[parthenogenesis] shouldn't work, apart from imprinting. It works in other

animals, from birds on down. " He said it seems Kono's team has found a way

around genetic imprinting.

 

He said that may lead to a new way to create stem cells used to grow new

tissues for sick people, thus avoiding use of human embryos to harvest stem

cells. In any case, Seidel said, the new results " tell us something about

control of the imprinting process. " That could be important because several

genetic diseases are known to result from faulty gene imprinting.

 

The team in Japan saw evidence that imprinting influences perhaps 1,000 or

so other genes, and " it's amazing that altering the expression of just two

imprinted genes can have a ripple effect on the rest of the genome, "

Australian scientists wrote in a commentary in the journal Nature.

 

David Loebel and Patrick Tam at the Children's Research Institute of the

University of Sydney added that the work provides evidence that " expression

of imprinted genes is one of the major reasons why natural parthenogenesis

has not been possible. What is not understood is why such a barrier in

single-parent reproduction has evolved. "

 

Harvard biologist David Haig suggests it's a matter of continuing

competition between the sexes. He suggested that the father's genes and the

mother's genes compete to influence the future. For example, Dad's genes

want to make big, healthy males who are likely to pass his genes along.

Mom's genes try to steer energy into keeping her healthy, allowing her to

reproduce again, perhaps with different males, increasing chances of passing

her genes along.

 

In effect, it's perhaps the battle of the sexes - writ small.

2004, Newsday, Inc.