You may have heard of Dolly the sheep; the first mammal created from an adult somatic cell over 20 years ago. She has often been called the most famous sheep in the world- although admittedly the only non-fictional sheep that springs to mind. Her birth in 1996 was a huge milestone in genetics and her body is proudly displayed in the National Museum of Scotland in Edinburgh. Since Dolly nearly two dozen species of mammals have been cloned but recently it was revealed that Chinese scientists had cloned a monkey for the first time.
Until now, the somatic cell nuclear transfer technique used to create Dolly has been unsuccessful in primates. This technique involves replacing an egg nucleus with the nucleus of a non-reproductive (somatic) cell that you want to clone, applying a current to the cell to mimic fertilisation and implanting into a surrogate. The result is offspring that are genetically identical to the somatic cell nucleus donor.
Mu-Ming Poo’s team used the same method but added messenger RNA and trichostatin A to the cocktail of nutrients and growth factors that enable the embryos to grow before being implanted into a surrogate. These added ingredients ‘switch on’ the genes required for further embryonic development. This seems to be the key to enabling development past the early blastocyst stage, where all previous attempts had failed to progress beyond. They implanted 79 embryos into 21 surrogates and the macaques Zhong Zhong and Hua Hua were the only two live births. Dolly was created from an adult somatic cell but the macaques were cloned from foetal connective tissue cells as this proved easier to clone (Coghlan, 2018).
This all may seem like a lot of hassle, so why clone at all? For years we have used animals as a model to study human disease. Clones significantly reduce the amount of genetic variation, enabling us to conclude with greater certainty that the result of a treatment is in fact due to the treatment rather than genetic variation.
Believe it or not the genome of macaques has 93% identity with humans. This means that 93% of our DNA is the same as macaques, due to us having relatively recent common ancestors (Rhesus Macaque Genome Sequencing and Analysis Consortium, 2007). This is of particular interest for complex human diseases such as Alzheimer’s and Parkinson’s. Previously, treatments for these diseases had been successful when tested on mice but failed when trialled in humans. This is where cloned monkeys come in – they could provide a better model for these complex diseases due to their similarity with humans. Furthermore, gene editing (such as CRISPR-Cas9) is already being used on developing embryos of monkeys, but this leaves some cells unedited so affects the certainty of the results. Combining cloning of monkeys with gene editing could produce offspring that are genetically edited to model human genetic disorders, such as Parkinson’s, in primate brains (Cyranoski, 2018).
As macaques are so similar to humans, the ability to clone them inevitably raises the prospect of human cloning. The ethical issues associated with cloning will be forever ongoing. With every development related to genome editing or cloning there is brief panic about human cloning and designer babies. The reality is that it hasn’t happened yet, and probably still won’t happen. Apart from it being illegal in most countries, there is no logical or ethical reason why anybody would want to clone humans.
So, while monkey clones are an exciting step forward in science, I wouldn’t get too concerned about the prospect of human clones walking amongst us just yet.