国产热热热精品,亚洲视频久久】日韩,三级婷婷在线久久,99人妻精品视频,精品九热人人肉肉在线,AV东京热一区二区,91po在线视频观看,久久激情宗合,青青草黄色手机视频

   

Scientists make human embryo clones

(Agencies)
Updated: 2008-01-17 23:39

 

 A scientist conducts research on stem cells at a laboratory. Japanese scientist Shinya Yamanaka has said that stem cell technologies could be used to cure diseases and heal injuries within 10 years. [File]

New York -- Scientists in California say they have produced embryos that are clones of two men, a potential step toward developing scientifically valuable stem cells.

The new report documents embryos made with ordinary skin cells. But it's not the first time human cloned embryos have been made. In 2005, for example, scientists in Britain reported using embryonic stem cells to produce a cloned embryo. It matured enough to produce stem cells, but none were extracted.

Stem cells weren't produced by the new embryos either, and because of that, experts reacted coolly to the research.

"I found it difficult to determine what was substantially new," said Doug Melton of the Harvard Stem Cell Institute. He said the "next big advance will be to create a human embryonic stem cell line" from cloned embryos. "This has yet to be achieved."

Dr. George Daley of the Harvard institute and Children's Hospital Boston called the new report interesting but agreed that "the real splash" will be when somebody creates stem cell lines from cloned human embryos.

"It's only a matter of time before some group succeeds," Daley said.

Korean scientist Hwang Woo-suk claimed a few years ago that he'd created such cell lines, but that turned out to be a fraud.

Dr. Samuel Wood, a co-author of the new paper and chief executive of Stemagen Corp. of La Jolla, Calif., said he and his colleagues are now attempting to produce stem cell lines from the embryos.

The work was published online Thursday by the journal Stem Cells.

Scientists say stem cells from cloned embryos could provide a valuable tool for studying diseases, screening drugs and, perhaps someday, creating transplant material to treat conditions like diabetes and Parkinson's disease.

But critics raise objections. The process "involves creating human lives in the laboratory solely to destroy them for alleged benefit to others," said Richard Doerflinger, spokesman for the US Conference of Catholic Bishops.

Citing the earlier work in Britain, he also said that as a scientific advancement, the new work was "very limited."

Other objections to cloning include concerns about health risks and exploitation if large numbers of women are asked to provide eggs.

Those objections are one reason that an alternative route to stem cells made headlines last November. Scientists reported a relatively simple way to turn skin cells directly into stem cells. This direct reprogramming carries a theoretical risk of cancer for the recipients of tissue from these cells, however, and many scientists have urged that work continue on the cloning technique as well.

The cloning approach involves inserting DNA from a person into an egg, and then growing the egg into an embryo about five days old before extracting the stem cells. At that stage, the embryo is a sphere of about 150 cells.

In the new work, researchers took skin cells from Wood and another volunteer and produced three embryos with DNA matching the men's. Further DNA testing on one of these embryos strengthened the case that it was a clone, researchers said.



Top World News  
Today's Top News  
Most Commented/Read Stories in 48 Hours
乳源| 宁夏| 垦利县| 耒阳市| 方正县| 南木林县| 桂平市| 全南县| 花莲市| 蓬莱市| 噶尔县| 屯留县| 鹿邑县| 曲水县| 大洼县| 治县。| 庄浪县| 鄂托克旗| 淮阳县| 岚皋县| 应用必备| 汶上县| 丰顺县| 奇台县| 满城县| 牡丹江市| 北海市| 清原| 徐州市| 广丰县| 什邡市| 从江县| 博湖县| 柯坪县| 英吉沙县| 晋城| 方山县| 农安县| 正镶白旗| 朔州市| 尼勒克县|