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While kangaroos and koalas are better known, researchers studying marsupials often use opossums in laboratory experiments because they are smaller and easier to care for. Gray short-tailed opossums, the species used in the study, are related to white-faced North American opossums, but they are smaller and lack pouches.

Researchers at Riken used CRISPR to delete or destroy a gene that codes for pigment production. Targeting this gene meant that if the experiments worked, the results would be clear at a glance: opossums would be albino if both copies of the gene were removed, and mottled or mosaic if a single copy was deleted.

The resulting litter included an albino opossum and a mosaic opossum (pictured above). The researchers also bred both, resulting in a herd of fully albino opossums, showing that coloration is an inherited genetic trait.

Researchers had to overcome several hurdles to edit the opossum genome. First, they had to calculate the timing of hormone injections to prepare the animals for pregnancy. The other challenge was that the marsupial eggs developed a thick layer around them, called the mucoid shell, soon after fertilization. This makes it difficult to inject the CRISPR treatment into cells. Kiyonari says in their first attempt, the needles would either not penetrate the cells or would damage the cells so that the embryos could not survive.

The researchers realized that it would be much easier to inject at an earlier stage, before the coating around the egg had hardened too much. By varying when the lights were turned off in the labs, the researchers mated the opossums later in the evening so the eggs would be ready to run in the morning after about a day and a half.

The researchers then used a tool called a piezoelectric drill, which uses an electric charge to more easily penetrate the membrane. This helped them inject without damaging the cells.

“I think this is an incredible result,” he says. Richard Behringer, a geneticist at the University of Texas. “They have shown that it can be done. Now is the time to do the biology,” he adds.

VandeBerg, who tried to establish the first colony of laboratory opossums in 1978, says opossums have been used as laboratory animals since the 1970s, and researchers have been trying to edit their genes for at least 25 years. full sequence genome, in 2007.

Comparative biologists hope that the ability to genetically modify opossums will help them learn more about some unique aspects of marsupial biology that have yet to be decoded. “We’re finding genes and marsupial genomes that we don’t have, which creates a bit of a mystery as to what they do,” he says. Rob MillerD., an immunologist at the University of New Mexico who uses opossums in his research.