1. Center for Reproductive Sciences, University of California, San Francisco, CA 94143, USA
2. Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Francisco, CA 94143, USA
3. Department of Comparative Biology and Experimental Medicine, Faculty of Veterinary Medicine, University of Calgary, Calgary, AB T2N 4N1, Canada
4. Department of Anatomy, University of California, San Francisco, CA 94143, USA
5. The Eli and Edythe Broad Center for Regeneration Medicine and Stem Cell Research, University of California, San Francisco, CA 94143, USA
6. Biomedical Sciences Program, University of California, San Francisco, CA 94143, USA
7. Department of Pediatrics, University of California, San Francisco, CA 94143, USA
8. Department of Obstetrics and Gynecology, Columbia University, New York, NY 10032, USA
9. Department of Pathology, Columbia University, New York, NY 10032, USA
10. Herbert Irving Comprehensive Cancer Center, Columbia University, New York, NY 10032, USA
11. Human Embryonic Stem Cell Program, University of California, San Francisco, CA 94143, USA