Although kangaroos and koalas are well-known, researchers looking for marsupials often use opossums to test the lab, as they are small and easy to care for. The gray opossum, the colors used in this study, is closely related to the North American white-colored opossum, but it is smaller and has no pockets.
Researchers at Riken used CRISPR to remove, or knock down, a gene that produces pigment. Looking at this type means that if the test were to work, the results could be obvious: the opossums would be albino if all genes of the gene could be shaken, modified, or drawn, if one virus were removed.
The resulting debris included one albino opossum and one opossum (above). The researchers also brought in the two, which led to the discovery of albino opossums, which indicate that the color is a genetic predisposition.
The researchers had to deal with a number of difficulties in modifying the opossum genome. First, they need to know when to inject hormones so that the animals can prepare for pregnancy. Another problem was that marsupial eggs came out in circles, called mucoid shells, just after fertilization. This makes it difficult to inject CRISPR treatment into cells. In the first experiment, the needles may not allow the cells to break through or destroy them so that the eggs do not survive, says Kionary.
The researchers found that it would be easier to inject early, coating around the egg before it became firm. When the lights were switched off in the labs, the researchers made the opossums to be mated in the evening so that the eggs would be ready for use in the morning, about a day and a half later.
The researchers used a device called a piezoelectric drill, which uses an electric motor to easily penetrate the membrane. This allowed them to inject cells without damaging them.
“I think that’s a good result,” he says Richard Behringer, a geneticist at the University of Texas. “They have shown that it can happen. Now is the time to do biology,” he adds.
Opossum has been used as a scientific animal since the 1970s, and researchers have tried to change their genes for at least 25 years, says VandeBerg, who first tried to make the first opossum laboratory in 1978. He was also the first marsupial to have our bodies in sequence, in 2007.
Biologists hope that the potential for altering opossums will enable them to learn more about some of the unique features of marsupial biology that have not been altered. “We find genes and marsupial genomes that we don’t have, so this creates a mystery to what they’re doing,” he says. Rob Miller, an infectious disease specialist at the University of New Mexico, who uses opossum in research.
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