By Jon Holmlund
This week’s news is that a group of Chinese researchers have birthed and studied a small number of rhesus monkeys that were “transgenic” for a human gene associated with brain development. In this work, monkey eggs (oocytes) were altered by adding the human form of a gene that is believed important to the development of the brain. This gene is one of the relative few that is different between humans and primates (monkeys, as in the work described here, or apes, such as chimpanzees or gorillas). That gene is abnormal in cases of human babies with small heads and brains, making it a good candidate for a gene that is critical to normal human brain development.
The gene was added to the monkeys’ egg cells using a viral delivery mechanism. The monkey genes were not, in this case, “edited” to the human form using CRISPR/Cas9. (Presumably, that experiment is coming.) Using the altered eggs, 8 monkey embryos were then conceived and implanted in females. Six of these survived to birth, and 5 of them lived long enough to do tests on their brains. These monkeys’ brains looked, on imaging studies and under the microscope, more like human brains than normal monkey brains do, and these monkeys’ brains developed more slowly than normal, mimicking the human situation, in which brain development occurs largely in late pregnancy and then a lot more in infancy and childhood. The five surviving monkeys also did better on some short-term memory tests than did “natural” monkeys given the same tests side-by-side. How strong this finding is appears debatable; the number of monkeys tested was small, and your correspondent cannot say how useful the tests are.
The scientists also took sperm from these transgenic monkeys and conceived three other monkeys (again, using IVF, they apparently did not try to breed the animals), all of which were sacrificed before birth, and whose brains apparently showed some of the same features as their “parents'” brains.
Genetically modifying non-human primates is generally frowned upon in the West, largely on grounds of the animals’ welfare, but in China, it’s full-speed ahead. The Chinese scientists apparently agree with Western scientists that the brains of apes (chimpanzees) should not be genetically altered because they are too much like us humans for comfort. Monkeys are not so close, in the Darwinian schema.
The investigators in this case think they are learning important lessons about the genetics of human brain development in a model that is enough like humans to be informative. They also think they are shedding light on human evolution (assuming that the evolutionary model is correct). Those conclusions seem to be a reach. The gene in question had already been identified as a candidate of interest, and its association with brain development arguably could be studied in other ways, within the ethical bounds of human subject research. And it seems unlikely that a creature such as created in this work would ever have arisen from random mutation. Rather, these transgenic monkeys seem to be an artifact of the investigators’ design, with uncertain relevance.
In any event—off to the races. Anticipate more work to alter monkeys’, if not eventually apes’, brains genetically. They might get something really interesting—and hard to know quite what to do with.