Although kangaroos and koalas are more famous, researchers who study marsupials often use possums in laboratory experiments because they are smaller and easier to care for. The species used in the study, the gray short-tailed possum, is related to the white-faced North American possum, but they are smaller and have no pouches.
Researchers at Riken use CRISPR to delete or knock out genes that code for pigment production. Targeting this gene means that if the experiment is successful, the results are clear: if both copies of the gene are knocked out, the possum will become albinism, and if one copy is deleted, the possum will become mottled or mosaic.
The resulting litter includes an albino possum and a mosaic possum (pictured above). The researchers also bred these two, which resulted in a litter of completely albino possums, indicating that this color is an inherited genetic trait.
Researchers had to overcome some obstacles to edit the possum genome. First, they must determine the timing of the hormone injections so that the animals are ready for pregnancy. Another challenge is that marsupial eggs form a thick layer around them shortly after fertilization, called mucus shells. This makes it more difficult to inject CRISPR treatment into cells. Kiyonari said that in their first attempt, the needle either couldn’t penetrate the cells or damaged them so that the embryo could not survive.
The researchers realized that it would be much easier to inject at an early stage before the coating around the egg becomes too hard. By changing the time the laboratory turns off the lights, the researchers allowed the possums to mate later in the evening so that the eggs could start working in the morning about a day and a half later.
The researchers then used a tool called a piezoelectric drill, which uses electrical charges to more easily penetrate the membrane. This helps them inject cells without damaging them.
“I think this is an incredible result,” said Richard Bellinger, A geneticist at the University of Texas. “They have proven that it can be done. Now is the time for biological research,” he added.
Since the 1970s, opossums have been used as laboratory animals. Researchers have been trying to edit their genes for at least 25 years. VandeBerg said that in 1978, he started trying to create the first laboratory possum colony. They are also the first marsupials with their own genes. Complete genome sequencing, In 2007.
Comparative biologists hope that the ability to genetically modify possums will help them learn more about some unique aspects of marsupial biology that have not yet been decoded. “We found genes and marsupial genomes that we didn’t have, so this created some mysteries about what they were doing,” said Rob Miller, An immunologist at the University of New Mexico, he used possums in his research.