1. Departments of Developmental Biology and Genetics, Stanford University School of Medicine, Stanford, CA 94305, USA
2. Biochemistry Section, Surgical Neurology Branch, NINDS, National Institutes of Health, Bethesda, MD 20892, USA
3. Department of Neuropathology, University of Bonn, 53105 Bonn, Germany
4. BD Biosciences CLONTECH, Palo Alto, CA 94303, USA