Chinese scientists have succeeded in cloning a rhesus monkey, now two years old and healthy, by refining the technique that gave birth to Dolly the sheep in 1996, according to a study published in the journal Nature Communications (New Window). brought.
Primates are particularly difficult to clone, and scientists had to fail for years before succeeding.
They hope their new technique, which uses the placenta, will lead to the creation of identical rhesus macaques for medical research.
Since Dolly the sheep was cloned using somatic cell nuclear transfer (SCNT) technology in 1996, more than 20 different mammals have been created using this technique: dogs, cats, pigs and cattle.
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Dolly the sheep was introduced to the media on February 22, 1997.
Photo: Portal
But it wasn't until 20 years later that scientists managed to clone the first primate. A pair of genetically identical crab-eating macaques named Hua Hua and Zhong Zhong were born in 2018 from SCNT at the Institute of Neuroscience of the Chinese Academy of Sciences in Shanghai, led by Qiang Sun, the study's first author.
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Hua Hua and Zhong Zhong
Photo: Chinese Academy of Sciences Shanghai
This was a scientific breakthrough, although less than 2% of the cloned crab-eating macaques were alive at birth. All attempts to clone rhesus macaques (Macaca mulatta, a species that gave its name to the blood group system) had otherwise failed.
The team from the Chinese institute investigated the reasons for this failure and identified the root cause: the placentas that provide the nutrients necessary for the growth of the cloned embryos had, compared to the placentas that resulted from in vitro fertilization of uncloned monkeys, anomalies.
The researchers therefore replaced the cells of the future placenta, called trophoblasts, with those of a healthy, non-cloned embryo. This technique significantly improved the success rate of SCNT cloning and led to the birth of the cloned rhesus monkey. His name is Retro and he is now two years old, Qiang Sun told AFP.
One downside: Only one of the 113 original embryos survived, a success rate of less than 1%, notes Lluis Montoliu of Spain's National Center for Biotechnology, who was not involved in the research.
If humans were to one day be cloned – the great fear in this field of research – we would first have to succeed in cloning other primate species, argues this scientist from the British Science Media Center (SMC).
The low success rate of this research confirms that human cloning is not only unnecessary and questionable, but, if attempted, would be extremely difficult and ethically unjustifiable, commented Lluis Montoliu.
An opinion shared by Qiang Sun, who considers human cloning to be unacceptable under any circumstances.
The SCNT (Somatic Cell Nucleus Transfer) reproductive cloning technique involves creating a genetic copy of an animal by replacing the nucleus of an unfertilized egg with a cell from the donor animal's (somatic) body to form an embryo that can be transferred into the uterus of a surrogate mother.
A rhesus monkey named Tetra had already been cloned in 1999 using a different embryo division technique. A simpler process, but can only produce four clones at a time.
So scientists have focused on SCNT in part because it can create many more clones, with the goal of creating genetically identical monkeys to study certain diseases and test drugs.