1. A. E. Oro, Howard Hughes Medical Institute, Departments of Dermatology, Developmental Biology, and Genetics, Stanford University School of Medicine, Stanford, CA 94305–5427, USA.
2. K. M. Higgins and M. P. Scott, Howard Hughes Medical Institute, Departments of Developmental Biology and Genetics, Stanford University School of Medicine, Stanford, CA 94305–5427, USA.
3. Z. Hu, J. M. Bonifas, E. H. Epstein Jr., Department of Dermatology, San Francisco General Hospital, University of California, San Francisco, CA 94110, USA.