1. Diabetes Center, University of California San Francisco (UCSF), San Francisco, CA 94122, USA.
2. Department of Pathology, UCSF, San Francisco, CA 94143, USA.
3. Program in Epithelial Biology, Cancer Biology Program, Stanford University School of Medicine, Stanford, CA 94305, USA.
4. Department of Pediatrics, UCSF, San Francisco, CA 94122, USA.