'Surrogate sires' could create specially bred livestock, say scientists
Scientists have used gene-editing to create pigs, goats and cattle that can serve as so-called “surrogate sires” – male animals providing sperm that carry the genetic traits of elite donor animals – in a bid to tackle global food insecurity.
For thousands of years, farmers have selectively bred livestock to champion superior traits such as disease resistance and heat tolerance, but techniques such as artificial insemination are often limited by technical and logistical challenges.
But by using the gene-editing tool Crispr-Cas9 – often likened to a pair of molecular scissors – to remove a gene that is specific to male sterility, the hope is farmers can use a more efficient approach to address the growing challenges of global food insecurity, climate change, and endangered species.
The scientists created sterile, but otherwise healthy mice, pigs, goats and cattle. The animals were then transplanted with sperm-producing stem cells from donors – resulting in the production of donor sperm.
So far, surrogate mice have fathered healthy offspring bearing donor mice genes, providing key proof of concept for the technique. But it is early days for the researchers, who are still finetuning the process for the larger animals and expect to generate that data in the coming years.
This process ensures the surrogate sire is not producing a product that is gene-edited, because the output is coming from a donor whose genetic code has not been tinkered with, highlighted study author Jon Oatley of Washington State University.
“The surrogate sire, even though he’s gene-edited … is serving as a vessel to produce an animal that would then go in and provide products for human consumption.”
This is a departure from controversial genetically modified (GM) organisms, which entail the transfer of entire genes or groups of genes from one species to another. Gene-editing, however, is a form of genetic engineering that tweaks a living genome by deleting, modifying, or replacing DNA.
“Sometimes … it’s not appreciated that we have been engineering animals for probably 10,000 years – ever since domestication of livestock,” Oatley said.
“They were combining genetic material through forced reproduction, and therefore engineering a genome that may not have developed just through normal natural selection … we’re just doing it in a more precise and efficient manner.”
The potential for off-target effects – whereby a proverbial snip in one area could affect another part of the genome – is a risk that is being vigilantly screened for, the researchers said.
Meanwhile, Crispr has had some success in the livestock industry rendering animals resilient to opportune pathogens, for instance, researchers from the University of Edinburgh have made pigs that appear to be immune to a virus that costs the swine industry billions each year.
The major impediment to the widespread adoption of gene-editing technology is government regulation. In the EU, for instance, gene-editing of plants and animals is governed by the strict laws that govern GM organisms (GMOs). But the technology can easily be slotted into production in sparsely regulated South American countries such as Argentina and Brazil, the researchers said.
The technology is unlikely be commercialised if regulated as a GMO, said Dr Alison Van Eenennaam from the University of California, who was not involved in the study.
These researchers have a long way to go in proving the technology works in actual livestock but public perception, which plays a role in shaping regulation, will probably be swayed by activist groups that have historically mounted intense opposition, she stressed.
“All that does is slow down the rate of genetic improvement, which has a negative impact on the overall sustainability of agriculture.”
Prof Bruce Whitelaw — another author of the surrogate sire study — struck a more optimistic tone, suggesting societal attitudes were changing.
“I wouldn’t go as far as to say that there is general acceptance around gene-editing technology, but there certainly is a shift in realising that this technology can contribute.”