[1] Univ Calif San Francisco, Howard Hughes Med Inst, Dept Anat, San Francisco, CA 94143 USA
[2] Univ Calif San Francisco, Howard Hughes Med Inst, Dept Biochem & Biophys, Program Cell & Dev Biol, San Francisco, CA 94143 USA
[3] Univ Calif San Francisco, Howard Hughes Med Inst, Dept Biochem & Biophys, Neurosci Program, San Francisco, CA 94143 USA
[4] Natl Def Med Coll, Dept Physiol, Tokorozawa, Saitama 359, Japan
[5] MIT, Whitehead Inst Biomed Res, Cambridge, MA 02142 USA
[6] MIT, Dept Biol, Cambridge, MA 02142 USA
[7] Jackson Lab, Bar Harbor, ME 04609 USA