1. Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3EG, UK.
2. The Anne McLaren Laboratory for Regenerative Medicine, and the Centre for Trophoblast Research, University of Cambridge, Cambridge CB2 0SZ, UK.
3. Institute for Stem Cell Biology and Regenerative Medicine, Department of Obstetrics and Gynecology, Stanford University School of Medicine, Stanford, CA 94305, USA.
4. Department of Surgery, University of Cambridge, Cambridge CB2 0QQ, UK.
5. Centro de Investigación Principe Felipe & Instituto Valenciano de Infertilidad (IVI) Valencia University, Avda. Autopista del Saler 16-3, 46015 Valencia, Spain.