In what is arguably an ethically controversial study, a team of scientists in China have inserted a gene involved in human brain development into the genomes of monkeys. In follow-up experiments, they tested whether the modified monkeys performed better than their control peers in cognitive tasks. The study is published in the journal National Science Review.
Scientists inserted the human gene MCPH1 into 11 rhesus monkeys, five of which survived long enough to have their mental abilities tested. According to the team’s findings, the transgenic monkeys did better on memory tests and reaction time trials compared to the non-gene-edited group.
In one such memory test, the monkeys were required to remember the color and shape of a stimulus that popped up on the screen for a specified amount of time. “Remarkably, our preliminary cognitive test detected an improved short-term memory in the [transgenic] monkeys,” wrote the team.
The monkeys’ brains did not differ in size compared to the control group, but they did take longer to develop. Brain image and tissue section analyses suggested that the transgenic monkeys were delayed in neuronal development and myelination – the process of membrane generation that wraps around nerve fibers to help speed up the transmission of nerve impulses. According to the team, this is similar to the developmental delay in humans called neoteny.
“One hallmark difference between humans and nonhuman primates is that humans require a much longer time to shape their neuro-networks during development, greatly elongating the childhood, i.e. the so-called 'neoteny,'” write the authors.
The research was conducted by the Chinese Academy of Sciences' Kunming Institute of Zoology in partnership with US scientists at the University of North Carolina.
The experiment has fueled flames in the ethics arena, garnering concern from some in the science community. Many countries would not allow such research to continue, stating that it crosses ethical boundaries.
"The first ethical issue concerns whether this research is scientifically sound enough to justify the use of animals," Jacqueline Glover, a University of Colorado bioethicist, told IFLScience. "Are the research methods able to answer the questions that the scientists are asking – if not – that's the first hard stop."
"The second issue concerns whether it is appropriate to use monkeys in particular. Can this research be done with alternatives that do not involve risks to nonhuman primates? Jim Sikela, a colleague at the University of Colorado, has pointed out that there are organoids available (i.e. modified cells in culture) from both humans and chimps that mimic many of the molecular/cellular characteristics of the brain. Groups are putting human genes in chimp brain oganoids as an alternative to using living primates for getting information about how human brain genes work."
While some have called the study a slippery slope in genetics research, others are less concerned.
“The genome of rhesus monkeys differs from ours by a few percent,” Larry Baum, a researcher at Hong Kong University's Centre for Genomic Sciences, told MIT Technology Review. "That’s millions of individual DNA bases differing between humans and monkeys.”
The study only changed a few of those bases in a gene of thousands. “You can decide for yourself whether there is anything to worry about.”
"Animal use guidelines vary across the globe but there is a shared commitment to only using animals if there is no alternative, using the least number of animals for scientific validity and using humane methods for research," added Glover. "This last requirement is particularly challenging in that creating humanized monkeys could, in itself, be inhumane because of the physical, psychological and social harms that it entails."
The team concluded: “Our findings demonstrated that transgenic nonhuman primates (excluding ape species) have the potential to provide important – and potentially unique – insights into basic questions of what actually makes humans unique as well as into disorders and clinically relevant phenotypes, such as neurodegenerative and social behavior disorders that are difficult to study by other means. But such gains must invariably be weighed against potential ethical concerns.”