Miracle Monkey Brains Amazingly Made Bigger from Human Genes
Yes, we’ve all read the story.
How a bored doctor decided to use a few body parts lying around his lab. His boredom morphed into a famous monster, a novel, and countless movies at drive-in theaters during the 1950s and ‘60s.
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Frankenstein was well ahead of his time in terms of marketing. He was probably the first monster that understood the importance of branding — as his legend will outlive every one of us.
Real-life Frankenstein story?
In an attempt to enlarge a primate's brain, scientists spliced human genes directly into a monkey’s fetus¹. Amazingly, this experiment worked.
The research team combined brilliant minds from the Max Planck Institute of Molecular Cell Biology and Genetics in Germany and from the Central Institute for Experimental Animals in Japan. Together, they introduced a precise human gene, known as ARHGAP11B², into a marmoset monkey fetus. This enlarged the neocortex of its brain.
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The neocortex happens to be the most recent region of the brain to evolve. It is the outer shell of our brain and makes up over 75% of its entirety. The neocortex is perhaps the most human thing about us — as it is responsible for all the quirks and idiosyncrasies that make us unique — this includes our use of complex languages and reasoning.
Evolving from primates
Whenever our hominid ancestors jumped from the evolutionary tree of our chimpanzee kinfolks, their brains rapidly expanded. It actually tripled in size over a period of around three million years. In fact, their brains grew so rapidly that they were cramped, and this was what caused the distinct folding of the human neocortex into the wrinkles we have now.
Scientists have always maintained that several evolutionary factors were involved, but they believe that the ARGHAP11B gene was unique to hominids. It could’ve very well provided the mental boost to our distant ancestors, such as the Denisovans and Neanderthals.
The role of ARGHAP11B in human evolution
Many studies in the past have been conducted using ARHGAP11B. When it has been unnaturally expressed in ferrets and mice, neocortex enlargements were also observed. But this study was the first time it was used on a non-human primate with normal human expression levels. And it suggests that ARGHAP11B played a major role in the evolution of humans.
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ARGHAP11B was created in our ancestors about five million years ago. There was a genetic mistake made during the copying of the gene ARGHAP11A. In short, there was a substitution of one nucleotide base that led to the formation of ARHGAP11B. This caused the brain’s neuron-producing cells to make more of themselves for a longer time period, producing a bigger neocortex.
Response from the study’s lead author
“We found indeed that the neocortex of the common marmoset brain was enlarged and the brain surface folded,” said Michael Heide, who was the study’s lead author. “Its cortical plate was also thicker than normal.”
Heide also added:
“Furthermore, we could see increased numbers of basal radial glia progenitors in the outer subventricular zone and increased numbers of upper-layer neurons, the neuron type that increases in primate evolution.”
Ethical concerns are being raised
The scientists refer to these human-monkey hybrids as ‘transgenic non-human primates.’ As you would imagine, not all people are pleased with these kinds of experiments on primates. It raises all sorts of ethical issues. And it doesn’t help that human genes are inserted into these animals.
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This is why scientists can only use monkey fetuses for their studies, and they are taken via C-section after 100 days of growth. Letting these experiments extend past the fetal phase and allow such human gene-carrying monkeys to be born into the world would be unethical and irresponsible.
The study’s coauthor Wieland Huttner issued the following statement in a press release.
“We confined our analyses to marmoset fetuses because we anticipated that the expression of this human-specific gene would affect the neocortex development in the marmoset,” Huttner said. “In light of potential unforeseeable consequences with regard to postnatal brain function, we considered it a prerequisite — and mandatory from an ethical point of view — to first determine the effects of ARHGAP11B on the development of fetal marmoset neocortex.”
: Max Planck Press. (June 18, 2020). Human brain size gene triggers bigger brain in monkeys. https://www.eurekalert.org/pub_releases/2020-06/m-hbs061220.php.
: Michael Heide, Christiane Haffner, Ayako Murayama, Yoko Kurotaki, Haruka Shinohara, Hideyuki Okano, Erika Sasaki, Wieland B. Huttner. (July 31, 2020). Human-specific ARHGAP11B increases size and folding of primate neocortex in the fetal marmoset. https://science.sciencemag.org/content/369/6503/546.