New hybrid embryos are the most thorough mixing of humans and mice yet
Scientists have made embryos that are a lot mouse and a little bit human. With a little help, human stem cells can knit themselves into growing mouse embryos, populating the developing liver, heart, retina and blood, researchers report May 13 in Science Advances. Finicky human cells don’t tend to grow well in other animals. But in one of the new mouse embryos, 4 percent of its DNA was human — the most thorough mixing between human and mouse yet. That level of integration is “quite striking to me,” says Juan Carlos Izpisua Belmonte, a stem cell and developmental biologist at the Salk Institute for Biological Studies in La Jolla, Calif. If other scientists can replicate the findings, “it potentially represents a major advance,” says Izpisua Belmonte, who was not involved in the study. Such chimeras could help reveal how a single cell can give rise to an entire organism. More humanized animals could also prove valuable in studying diseases such as malaria that affect people...