By Lluís Montoliu - The Conversation
We have just learned about the cloning of a new species of primate, a Rhesus monkey (
Macaca mulatta
).
This work has been carried out by a team of researchers in China, the same laboratory that, six years ago, already demonstrated the cloning of another species of primate: the crab-eating macaque.
Dolly, a star of science
Immediately, this news and the word “cloning” leads us to remember Dolly the sheep.
If we ask any person on the street if they are familiar with Dolly the sheep, I am sure that the majority would answer yes, that they know or have heard of the first animal cloned from adult cells.
This only happens with a small number of advances or scientific news, the few that manage to cross the threshold of interest of specialists and reach the entire society.
There is a before and after in scientific dissemination with Dolly.
Society's interest in science increased significantly after that historical milestone.
The publication in Nature magazine of Dolly's birth, in February 1997, sparked a multitude of reactions and articles, from the most sensible and reasonable to the most imaginative, fearful that animal cloning could reach human beings, something that quickly was banned and has not happened.
The truth is that the team of Scottish researchers at the Roslin Institute demonstrated what Hans Spemann, German embryologist and Nobel Prize winner, had anticipated 70 years earlier, when he proposed an experiment to demonstrate that the nucleus of a cell did not lose components as it transformed. in a more specialized cell.
That any nucleus of a cell in an animal's body retained the ability to once again support complete embryonic development, giving rise to a cloned animal.
During the decades of the 50s and 60s of the last century, various researchers demonstrated that cloning was possible, using different species of amphibians.
He highlighted the work of Sir John Gurdon, a British embryologist who used African frogs to demonstrate that he could obtain adult animals from the nuclei of cells in the intestines of tadpoles.
However, success was slow to reach mammals.
More than 30 years passed before the team of researchers led by Ian Wilmut and Keith Campbell informed the world of Dolly's birth.
After 300 attempts
The technique used to obtain Dolly the sheep was relatively simple.
The genetic material was emptied from an egg and the nucleus of an adult cell was introduced.
After an electrical spark and after implanting the embryo thus reconstructed in the uterus of a female of the animal in question, a cloned animal could be obtained, with very low efficiency.
Dolly was the only sheep born after almost 300 reconstructed embryos.
After the sheep, other mammal species were cloned, adapting in each case the method to the characteristics of the reproductive biology of each species, which was not easy at all.
In 1998 the first cows and mice were obtained.
A year later the goat was cloned.
The first cloned pig was born in 2000 and two years later it was the cat and rabbit's turn.
In 2003, the first clones of rats and horses were obtained, while the dog was not achieved until 2005.
primate time
The fear that the cloning technique could reach humans gradually lost interest when it became clear how difficult it was to try it on other species of primates, like us.
Indeed, it was not until 2018 when a team of Chinese researchers announced the cloning of the crab-eating macaque, the same team that has now just announced that of the Rhesus monkey.
In both the 2018 experiment and the current one, this laboratory reports very low cloning efficiencies, less than 1%.
They are similar to those obtained with Dolly, 27 years later.
It is confirmed that it is possible to clone primates, but the method remains very ineffective for its possible use in biomedical research.
Additionally, these experiments with non-human primates are prohibited in Europe, unless they refer to very serious, fatal diseases that affect us or those species.
Limited usefulness
What purpose has animal cloning been used for?
Firstly to study the earliest phases of mammalian embryonic development.
In 2012, the Nobel Prize in Medicine went to John Gurdon, the frog cloner, and Shinya Yamanaka, who deciphered the genes necessary to reprogram the nucleus of any cell and turn it into a stem cell.
The award did not recognize the merits of the Scottish team responsible for Dolly, probably due to a series of unfortunate incidents and complaints that occurred around that experiment, which was destined to be one of the milestones of the century.
The cloning of farm animals (cows, sheep, goats, pigs, rabbits...) made it possible to obtain genetically modified specimens in a much simpler and more efficient way, using nuclei from previously genetically modified cells that gave rise to those animals with the same genetic modification.
The pigs currently used for xenotransplantations were obtained through cloning.
And also many other animal models to study human diseases in species other than the mouse, which until then was one of the few that could be easily genetically modified.