For the first time, a stem cell model has produced a structure resembling an early human embryo with a yolk-sac-like structure, from a single starting stem cell population and without direct genetic manipulation. The models were made at University of Michigan Engineering. Researchers at the Chinese Academy of Sciences provided monkey embryo data to help confirm that the Michigan team was indeed seeing a yolk-sac-like structure in their models. The work is published in the journal Nature Cell Biology.