Mouse Embryo (IMAGE) University of Copenhagen Caption The picture shows a 9.5-day-old mouse embryo including extra-embryonic tissue. The red region marks embryonic stem cells in the extra-embryonic yolk sac. Embryonic stem cells are not normally able to do this, but when cells are pushed backwards in development as described in Morgani et al. Credit Sophie Morgani, University of Copenhagen. Usage Restrictions Please credit: Sophie Morgani, University of Copenhagen. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.