While kangaroos and koalas are more well-known, researchers who study marsupials often use opossums in lab experiments, since they are smaller and easier to care for. The gray short-tailed opossum, the species used in the study, is related to the white-faced North American opossum, but is smaller and does not have a cyst.
The researchers at Riken used CRISPR technology to delete or delete the gene that codes for pigment production. Targeting this gene means that if the experiments are successful, the results will be clear at a glance: an albino opossum would be an albino if two copies of the gene were deleted, and a mottled, or mosaic, if one copy was deleted.
The resulting litter included an albino opossum and one mosaic opossum (pictured above). The researchers also bred the two, resulting in a population of all-white opossums, which indicates that the coloration was an inherited genetic trait.
The researchers had to overcome some hurdles to edit the opossum genome. First, they had to time the injections of hormones to prepare the animals for pregnancy. Another challenge was that marsupial eggs form a thick layer around them, called the mucosal cortex, soon after fertilization. This makes it difficult to inject the CRISPR treatment into the cells. Kionari says the needles in their first attempts either don’t penetrate cells or damage them so that the embryos can’t survive.
The researchers realized that it would be much easier to do the injection at an early stage, before the shell around the egg became too tough. By varying the lights out in the labs, the researchers got the opossum to mate later in the evening so that the eggs would be ready to work in the morning, about a day and a half later.
Then the researchers used a tool called a piezoelectric drill, which uses an electric charge to penetrate the membrane more easily. This helped them inject the cells without damaging them.
“I think it’s an amazing result,” he says. Richard Bringer, a geneticist at the University of Texas. “They have shown that it can be done. Now is the time to study biology.”
Opossums have been used as laboratory animals since the 1970s, and researchers have been trying to modify their genes for at least 25 years, says VandeBerg, who began trying to establish the first laboratory opossum colony in 1978. They were also the first marsupials to own them. Whole genome sequencing, in 2007.
Comparative biologists hope that the ability to genetically modify the opossum will help them learn more about some unique aspects of marsupial biology that have yet to be decoded. “We found genes and genomes of marsupials that we don’t have, and that creates some mystery about what they do,” Rob Miller, an immunologist at the University of New Mexico, who uses the opossum in his research.