Scientists edit embryos' genes to study early human development

British scientists have used agenome editing tool known as CRISPR/Cas9 to knock out a gene inembryos just a few days old, testing the technique's ability todecipher key gene functions in early human development.

The researchers said their experiments, using a technologythat is the subject of fierce international debate because offears that it could be used to create babies to order, willdeepen understanding of the biology of early human development.

CRISPR/Cas9 can enable scientists to find and modify orreplace genetic defects. Many describe it as game-changing.

"One way to find out what a gene does in the developingembryo is to see what happens when it isn't working," said KathyNiakan, a stem cell scientists who led the research at Britain'sFrancis Crick Institute.

"Now we have demonstrated an efficient way of doing this, wehope that other scientists will use it to find out the roles ofother genes."

She said her hope was for scientists to decipher the rolesof all the key genes embryos need to develop successfully. Thiscould then improve IVF treatments for infertile couples and alsohelp doctors understand why so many pregnancies fail.

'First step'

"It may take many years to achieve such an understanding,our study is just the first step," Niakan said.

Niakan's team decided to use it to stop a key gene fromproducing a protein called OCT4, which normally becomes activein the first few days of human embryo development.

They spent more than a year optimising their varioustechniques using mouse embryos and human embryonic stem cells inlab dishes, before starting work on human embryos.

To inactivate OCT4, they used CRISPR/Cas9 to change the DNAof 41 human embryos. After seven days, embryo development wasstopped and the embryos were analysed.

After an egg is fertilized, it divides until at about sevendays it forms a ball of around 200 cells called a blastocyst,Niakan explained in a briefing about her work.

Her results, published in the journal Nature on Wednesday,found that human embryos need OCT4 to form a blastocyst. Withoutit, the blastocyst cannot form or develop normally.

The British team's work comes on the heels of milestonescience in the United States, where scientists said in July theyhad succeeded in altering the genes of a human embryo to correcta disease-causing mutation.

Rob Buckle, chief science officer at Britain's MedicalResearch Council, praised Niakan's research and findings: "Genome editing technologies particularly CRISPR-Cas9 usedin this study are having a game-changing effect on our abilityto understand the function of critical human genes," he said.

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