A monkey has been born with fluorescent eyes and fingers in a world first. Here’s why

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Key points

  • A monkey “chimera” in China is the first primate born with a high level of stem cell-derived tissue.
  • A chimera is an organism that has at least two different sources of genetic material.
  • The scientists tagged the stem cells with a green protein, resulting in the monkey’s fluorescent eyes.
  • It’s the first time this technique was used to create a live monkey chimera.
  • The research could help accelerate research into brain disease.

A monkey born in China with fluorescent green eyes and fingertips is the first live primate “chimera” created with stem cells, researchers say, meaning the creature has tissue and DNA derived from two genetically distinct embryos.

The birth of the monkey is a leap forward in the study of regenerative medicine using stem cells and the realm of chimeric research, which could one day lead to animals such as pigs being used to grow human organs.

The monkey ‘chimera’ with fluorescent eyes and fingertips, created by genetic researchers in China.Credit: Cell, Cao et al

The crab-eating macaque, a common study species, was born from an embryo that researchers injected with stem cells derived from a separate embryo. The injected cells were tagged with a green protein, so the scientists could see which tissues grew from the stem cells.

The resulting animal had a high proportion of green-tinged tissue produced by the stem cells, including in its eyes, fingers, tail and up to 90 per cent of its brain, the authors of the Cell paper said. The monkey died after 10 days.

The technique could one day create monkeys with humanlike tissues or disease, which would let biomedical researchers more precisely screen drugs and test new therapies for afflictions such as ALS, the researchers said.

“This is a long-sought goal in the field,” senior author Dr Zhen Liu of the Chinese Academy of Sciences said.

“Specifically, this work could help us to generate more precise monkey models for studying neurological diseases as well as for other biomedicine studies.”

The ability to create genetically tweaked monkey chimeras would have profound impacts on medicine, co-author of the study and internationally renowned neuroscientist Professor Mu-ming Poo said.

“The reason to have monkey disease models is because monkey physiology is much closer to human. Mouse models, in many cases, don’t simulate human disease very well, especially for brain diseases,” he said.

The researchers spent years honing the best method of growing primate pluripotent stem cells – which are cells derived from embryos that can grow into any type of cell or tissue – in the lab.

In 2017 scientist grew a human-pig chimera embryo and took it a third of the way through pregnancy.Credit: SALK INSTITUTE/CELL

Creating a chimera is a key technique scientists use to test if their lab-grown stem cells can grow into viable tissues.

But scientists have long been constrained to mice and rats for this work. Progress in creating chimeras of our close evolutionary neighbours, non-human primates, has been much slower.

This study is important because it proves an embryo significantly altered by pluripotent stem cells can result in the live birth of a primate, said University of Melbourne stem cell expert Dr Alexandra Harvey.

“Since primate embryonic stem cells were first isolated in 1995, and then human in 1998, we’ve not really been successful in demonstrating the full potential of embryonic stem cells. You do that by using this gold standard test, which is the chimera,” Harvey said.

A colony of human pluripotent stem cells.Credit: NIH’s National Eye Institute

The results could also help other scientists find more effective ways of growing pluripotent stem cells for use in regenerative medicine, Harvey said.

“Any number of diseases – heart disease, stroke, spinal cord issues, cancers – could potentially have a solution in stem cells,” she said.

“But understanding how to grow them, how to make them into the cells we want, is really important. This study really sits in that area.”

Previous studies have reported monkey chimeras created with stem cells, but they either remained fetuses or only had a small proportion of stem cell-derived tissue and therefore weren’t true chimeras, the authors of the new Cell paper argue.

Three rhesus monkey chimeras named Roku, Hex and Chimero were born in 2012, but they were created by the fusion of several embryos, not from stem cells.

While the green-eyed monkey was a single-species chimera, scientists have created cross-species chimera embryos too. Scientists created a mouse embryo that was 4 per cent human in 2020 and a monkey-human embryo in 2021.

In September, researchers transplanted a pig-human chimera embryo into a surrogate pig mother, and the embryo grew kidneys containing mostly human cells.

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