[1] Stanford Med, Dev Biol, San Francisco, CA USA
[2] Univ Calif San Diego, Chem & Biochem, San Clemente, CA USA
[3] Univ Calif San Diego, Div Biol Sci, San Diego, CA 92103 USA
[4] Univ Munich, Gene Ctr, Munich, Germany
[5] Univ Oxford, Sir William Sch Pathol, Oxford, England
[6] Univ Calif San Diego, Natl Ctr Microscopy & Imaging Res, San Diego, CA 92103 USA
[7] Univ Calif, Leichtag 412,MC 0654, La Jolla, CA USA