1. Department of Pharmacology, Howard Hughes Medical Institute, and the Institute for Stem Cell and Regenerative Medicine, University of Washington School of Medicine, Seattle, WA 98109, USA.
2. Division of Dermatology, University of Washington School of Medicine, Seattle, WA 98195, USA.
3. Department of Pathology and Laboratory Medicine, The David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA.