1. Division of Cellular and Molecular Medicine, Department of Medicine, University of California, San Diego, 9500 Gilman Drive, La jolla, CA 92093-0651, U.S.A.
2. Howard Hughes Medical Institute, University of California, San Diego, 9500 Gilman Drive, La jolla, CA 92093-0651, U.S.A.
3. Division of Endocrinology and Metabolism, Department of Medicine, University of California, San Diego, 9500 Gilman Drive, La jolla, CA 92093-0651, U.S.A.