1. Babraham Institute 1 Epigenetics Programme , , Cambridge CB22 3AT , UK
2. Centre for Trophoblast Research, University of Cambridge 2 , Cambridge CB2 3EG , UK
3. Wellcome-MRC Cambridge Stem Cell Institute 3 , Cambridge CB2 0AW , UK
4. The Francis Crick Institute 4 , London NW1 1AT , UK
5. Embryology Research Unit, Children's Medical Research Institute, The University of Sydney 5 , Westmead NSW 2145 , Australia
6. School of Medical Sciences, Faculty of Medicine and Health, The University of Sydney 6 , Sydney NSW 2006 , Australia