1. The Jackson Laboratory, Bar Harbor, ME 04609, USA.
2. Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, FL 33136, USA.
3. Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, NC 27599, USA.
4. Department of Ophthalmology, Tufts University of Medicine, Boston, MA 02111, USA.
5. The Howard Hughes Medical Institute, Bar Harbor, ME 04609, USA.