1. A. H. Brivanlou is at the Rockefeller University, New York, NY 10021, USA.
2. F. H. Gage is at the Salk Institute for Biological Sciences, San Diego, CA 92037, USA.
3. R. Jaenisch is at the Whitehead Institute, Cambridge, MA 02142-1479, USA.
4. T. Jessell is a Howard Hughes Medical Institute investigator at Columbia University, New York, NY 10032, USA.
5. D. Melton is at Harvard University, Cambridge, MA 02138, USA.
6. J. Rossant is at Mount Sinai Hospital, Toronto, Ontario M5G 1X5, Canada.