1. H. Qi, M. Rand, S. Artavanis-Tsakonas, Howard Hughes Medical Institute, Yale University School of Medicine, Boyer Center for Molecular Medicine, 295 Congress Avenue, New Haven, CT 06536–0812, USA. X. Wu, Department of Genetics, Howard Hughes Medical Institute, Yale University School of Medicine, Boyer Center for Molecular Medicine, 295 Congress Avenue, New Haven, CT 06536–0812, USA, and Institute of Genetics, Fudan University, 220 Handan Road, Shanghai 200433, People's Republic of China. N. Sestan...