Was bedeuten diese emyos

NEW YORK, April 23 (Reuters) - Biologists in China reported carrying out the first experiment to alter the DNA of human embryos, igniting an outcry from scientists who warn against altering the human genome in a way that could last for generations.

The study from China appeared last weekend in an obscure online journal called Protein & Cell. In an interview published on Wednesday on the news site of the journal Nature, lead author Junjiu Huang of Sun Yat-sen University in Guangzhou said both Nature and Science had rejected the paper, partly for ethical reasons.

“There have been persistent rumors” of this kind of research taking place in China, said Edward Lanphier, chief executive of California-based Sangamo BioSciences Inc and part of a group of who called last month for a global moratorium on such experiments. “This paper takes it out of the hypothetical and into the real.”

The controversial technique is called CRISPR/Cas9, and represents a biological version of a word-processing program’s “find and replace” function. Scientists introduce enzymes that first bind to a mutated gene, such as one associated with disease, and then replace or repair it.

At least half a dozen experiments have been planned or are underway using CRISPR on human eggs or embryos to correct genetic defects such as those causing cystic fibrosis or the BRCA1 breast-cancer gene, the MIT magazine Technology Review recently reported.

Scientists warn that altering the DNA of human sperm, eggs, or embryos could produce unknown effects on future generations, since the changes are passed on to offspring. They distinguish this type of so-called germline engineering from that which alters the DNA of non-reproductive cells to repair diseased genes.

“It is too soon to apply these technologies to the human germ line, the inherited DNA, in a clinical setting,” said MIT biologist Rudolf Jaenisch, president of the International Society for Stem Cell Research.

Huang’s experiments provide evidence of what can go wrong with CRISPR. His team experimented on 86 one-cell human embryos, they reported, all from fertility clinics and, because of chromosomal defects, unable to develop into a baby. Their target was a gene called HBB, which can cause the blood disease beta-thalassemia.

About a dozen embryos did not even survive the genome-editing, the scientists reported.

Of the surviving embryos, many showed “off-target” effects, they reported, meaning genes other than HBB were altered. Other embryos suffered “untoward mutations.” Only a handful of embryos contained the healthy DNA meant to repair the defective HBB genes.

“If you want to do it in normal embryos, you need to be close to 100 percent” on target in terms of fixing only the target gene, Huang told Nature News, which reported that four or more groups in China are doing similar experiments. “That’s why we stopped.”

Science and Nature said their policy is not to comment on publication decisions. Springer, which publishes Protein & Cell and is owned by European private equity firm BC Partners, did not immediately reply to questions about its decision to publish Huang’s paper.

Lanphier fears that the call for a moratorium on editing the human germline is being ignored. “This is the first of what may be many papers” on human germline engineering, he said. (Reporting by Sharon Begley; Editing by Michele Gershberg and Andrew Hay)

CHICAGO (Reuters) - For blood cells to grow in an embryo, they need the pressure of a beating heart, U.S. researchers said on Wednesday.

A doctor is silhouetted as he walks past a poster showing images of the development of a human fetus at a fertility doctor in Rome June 6, 2005. REUTERS/Alessia Pierdomenico

The finding explains why an embryo’s heart starts beating just weeks after conception, and it points the way to new stem cell-based treatments for a host of blood disorders such as leukemia.

“In learning how the heartbeat stimulates formation of embryos, we’ve taken a leap forward in understanding how to direct blood formation from embryonic stem cells in the petri dish,” Dr. George Daley of Harvard Medical School and Children’s Hospital Boston, whose study appears in the journal Nature, said in a statement.

“These observations reveal an unexpected role for biomechanical forces in embryonic development,” Guillermo Garcia-Cardena of Brigham and Women’s Hospital in Boston, who worked on the study, said in a statement.

Stem cells are the body’s master cells, providing a renewable source of brain, bone, muscle, blood and other cells.

An embryo in the first days after conception is made up entirely of these cells, each of which can give rise to all of the cells and tissues in the body.

Daley’s team looked at how the stress of friction and the flow of fluid affected the formation of blood cells from mouse embryonic stem cells.

PROMOTING BLOOD

The study showed that these forces promote blood formation and increase the production of colonies of cells that give rise to specific types of blood cells.

Mouse embryos with a mutation that kept the developing heart from beating had far fewer of these so-called progenitor blood cell colonies.

In a separate study, a team led by Dr. Leonard Zon of Harvard and Children’s Hospital Boston, looked at the effects of the embryonic heartbeat in zebrafish, which have transparent embryos.

“We were looking in real aortas in real vertebrate embryos to see the actual stem cells,” Zon said in a statement.

The study published in journal Cell found that levels of nitric oxide, which is known to play a key role in blood vessel formation, increase when blood is flowing.

Mutant embryos that had no heart beat or circulation were found to have far lower levels of blood-forming stem cells known as hematopoietic progenitor cells.

Researchers think nitric oxide may work as a type of signal to start the process of blood stem cell production.

“This finding connects the change in blood flow with the production of new blood cells,” Zon said.

The findings may lead to new ways to coax iPS cells -- an which look and act like embryonic stem cells -- into producing blood-forming cells that could be used by people with leukemia who need bone marrow transplants, he said.

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