1. Section on Islet Cell and Regenerative Biology, Research Division, Joslin Diabetes Center, Boston, MA, USA.
2. Department of Genetics, Harvard Medical School, Boston, MA, USA.
3. Harvard Stem Cell Institute, Harvard Medical School, Boston, MA, USA.
4. Biology Department, Emmanuel College, Boston, MA, USA.
5. Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, USA.