[1] Stanford Univ, Sch Med, Inst Stem Cell Biol & Regenerat Med, Ctr Human Embryon Stem Cell Res & Educ,Dept Obste, Stanford, CA 94305 USA
[2] Univ Calif San Diego, Dept Neurosci, Howard Hughes Med Inst, San Diego, CA 92103 USA
[3] Univ Calif San Diego, Dept Pediat, Howard Hughes Med Inst, San Diego, CA 92103 USA