1. Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115
2. The Schepens Eye Research Institute, Department of Ophthalmology, Harvard Medical School, 20 Staniford Street, Boston, Massachusetts 02114
3. Department of Systems Biology, Harvard Medical School, Boston, Massachusetts 02115
4. Department of Medicine, Tufts Medical Center, Boston, Massachusetts 02111
5. School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138