A new gene editing method could eliminate disease-causing mutations in dogs. It could even clone individual dogs.
Being in South Korea two beagle dogs born using cloned skin cells modified with the gene editing technique CRISPR. CRISPR-processed dogs were once made using modified fertilized eggs. Now, for the first time, cloned skin cells form the basis.
Many purebred dogs carry disease-causing mutations in their DNA. With the help of gene editing, you could eliminate these without affecting other traits. DNA editing via cloning is more suitable for this than adapting fertilized eggs, says Okjae Koo of biotech company ToolGen. “The cloning method is more reliable for creating genetically modified purebred dogs,” says Koo.
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cell fusion
To create the cloned puppies, Koo and his colleagues first created genetically engineered skin cells. They modified the DJ-1 gene in it, so that a certain protein is no longer produced. Mutations in DJ-1 are linked to diseases such as Parkinson’s, so studying dogs that lack the associated protein could help develop treatments for these conditions.
In addition to knocking out DJ-1, the team added several genes, including one for a green fluorescent protein called GFP. Using this protein, the researchers could more easily see which cells had been successfully edited. The team does not plan to use these genes in future research, Koo says.
The team then placed the modified skin cells next to eggs that had had their DNA removed. The researchers then fused each skin cell with an empty egg by applying short electrical pulses. The resulting embryos were implanted into a surrogate mother.
The dogs are now 22 months old. They don’t show any abnormalities – other than their skin glowing green in ultraviolet light. Since diseases associated with DJ-1 are age-related, the dogs could still develop problems as they get older.
chimeras
A total of 68 embryos were transferred into six dogs. That resulted in two puppies — a success rate of about 3 percent. That is a comparable percentage to that in the study of Lai Liangxue of the Guangzhou Institute of Biomedicine and Health in China, who with his team the first CRISPR-processed dogs ever created – a feat they unveiled in 2015.
Those dogs, called Tiangou and Hercules, are beagles that have more muscle mass than normal due to the deletion of a gene. “Both Tiangou and Hercules are doing well,” says Lai. His team has since created several other dogs using the same method, he says.
Lai admits that the cloning technique used by the other South Korean team has advantages. When fertilized eggs are genetically edited, the resulting animals are usually ‘chimeras‘. That is, some of their cells are genetically engineered, but others are not. That means you have to keep breeding to create dogs whose cells all have the desired change, says Lai. With the cloning technique no further breeding is necessary.
Cloned Pets
Both Lai and Koo’s teams create dogs for medical research. However, cloning is also increasingly being used to make copies of beloved pets that have died, using tissue samples taken shortly after death.
In the United States, a company called ViaGen About 1,000 “cloned companion animals” have been created so far, a spokesperson told New Scientist. ViaGen charges $50,000 to clone a dog and $38,000 for a cat.
If you combine this cloning with gene editing, you could make these animals healthier. ViaGen does not currently offer any form of genetic modification, but does not exclude it in the future. “We are willing to consider all options that work, that are approved by the necessary regulatory authorities, that are good for the animals in question and that meet a need of society,” the spokesperson said.