[1] Yale Univ, Sch Med, Dept Therapeut Radiol, New Haven, CT 06520 USA
[2] Yale Univ, Sch Med, Dept Genet, New Haven, CT 06520 USA
[3] Scripps Res Inst, Dept Cell Biol, La Jolla, CA 92037 USA
[4] Scripps Res Inst, Dept Mol Biol, La Jolla, CA 92037 USA