1. Department of Cell Biology and Genetics; University of British Columbia; Vancouver BC; Canada; V6T1Z4
2. Faculty of Medicine, Stem Cell Epigenetics Laboratory, Institute of Basic Medical Sciences; University of Oslo, Norwegian Center for Stem Cell Research; Blindern; 0317 Oslo PO Box 1112; Norway
3. Department of Genetics; Yale Stem Cell Center, Yale School of Medicine, 10 Amistad 201B; New Haven; Connecticut; 06520