[1] Cambridge Inst Med Res, Dept Med Genet, Cambridge CB2 2XY, England
[2] Univ Michigan, Inst Life Sci, Ann Arbor, MI 48109 USA
[3] Univ Michigan, Dept Pathol, Ann Arbor, MI 48109 USA
[4] Novartis Inst Biomed Res, Cambridge, MA 02139 USA
[5] Univ Michigan, Dept Mol Cellular & Dev Biol, Ann Arbor, MI 48109 USA
[6] Univ Michigan, Dept Biol Chem, Ann Arbor, MI 48109 USA