In world’s first genetically engineered marsupials, scientists get a fresh window into human biology

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When the pile of opossums arrived at John VandeBerg’s lab from the Smithsonian’s National Zoo in 1978, the geneticist had an ambitious plan for the soft-eyed, hamster-sized animals. He wanted to domesticate them to live in a lab anywhere on the planet. Mice were well and good, but imagine what biomedical insights might be lurking inside marsupials, he thought. Their young, rather than being encased inside a uterus, develop attached to a nipple in a pouch or on a belly where they’re much easier to observe.

VandeBerg succeeded, and today manages the largest Monodelphis domestica colony in the world at the University of Texas Rio Grande Valley School of Medicine. More than a dozen labs have taken up research projects with the gray short-tailed opossums, who hail from South America. But the same quirk that makes them a compelling model organism has also made them more difficult to study than he once imagined.

Shortly after ovulation, marsupial moms secrete layers of mucus and protein around their eggs, covering them in a hard...