First there was Dolly the sheep: the pioneering mammal to be cloned using the somatic cell nuclear transfer technique (SCNT). A number of unnamed cows, pigs, dogs, cats, mice and rats followed. Now, 22 years after Dolly sparked fears of human cloning just around the corner, we have Zhong Zhong and Hua Hua: the first primates cloned using the technique.
“The barrier of cloning primate species is now overcome,” said Muming Poo from Shanghai’s Chinese Academy of Sciences. He went on to explain that Zhong Zhong and Hua Hua (the word “Zhongua” means “Chinese nation”) had shown that human cloning was theoretically possible – but added this was his team had no intention of exploring, opining that society would ban such research on ethical grounds.
Rather, the researchers’ goal was to create genetically identical monkeys for use in lab research. Our current scientific models chiefly use mice, which are very cheap and easy to create but often create false hope for medical breakthroughs which don’t scale up to humans. The ability to clone animals that are genetically closer to us could revolutionise medical research – although there are some caveats.
How does somatic cell nuclear transfer technique work?
As a quick primer, here is what SCNT involves. Scientists remove the DNA-containing nucleus from eggs of a creature, and replaced it with DNA from another. The modified eggs then grow and divide, eventually forming an embryo, which is moved to a female and grows to birth.
That’s the neat and tidy version anyway – the truth is still a fair bit more messy and inefficient: it took 127 eggs to get two monkey babies, and so far the scientists have only produced healthy clones with DNA from a monkey fetus, not a fully grown adult monkey. All the same, previous attempts to clone any primates via this method have not progressed onto the blastocyst stage. The team credit their success to preventing epigenetic changes to the DNA.
To be clear, Zhong Zhong and Hua Hua technically aren’t the first primate clones – that honour falls to Tetra, a rhesus macaque born in 1999. But Tetra was the product of embryo splitting, which is considerably less sophisticated than SCNT. Embryo splitting is exactly what it sounds like – it’s a man-made version of the process that produces identical twins in the womb. Its main limitation is scale: embryo splitting can produce a maximum of four clones.
A medical revolution
So if this isn’t for human cloning – a topic that understandably leaves people feeling squeamish – what’s the purpose? Medical science, chiefly.
Currently we tend to use rodents for medical studies as they’re easy to produce quickly and cheaply for large-scale experiments. The problem is that while they’re cheap, their genetic differences to humans leaves a lot of false dawns where treatments work on rats and mice, but fall flat when it comes to human studies. Genetically speaking, mice are just less robust than humans, so therapies that seem to work wonders on rodents often don’t scale up.
A steady supply of research monkeys has the power to target this weakness. “You can produce cloned monkeys with the same genetic background except the gene you manipulated,” explained senior author Qiang Sun. “This will generate real models not just for genetically based brain diseases, but also cancer, immune, or metabolic disorders and allow us to test the efficacy of the drugs for these conditions before clinical use.”
But not everywhere. Within the EU, use of primates for research is heavily regulated, and only permitted if other methods are unavailable. In some countries, it is banned outright. All the same, medical research is international – and the researchers say the have followed guidance laid out by the US National Institutes of Health for researching on animals.
The researchers will continue to refine the process, aiming to increase the success rate – all the while monitoring the process of Zhong Zhong and Hua Hua to ensure they’re developing normally both physically and mentally.
The research was published in Cell.
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