[1] NHLBI, LMC Genet & Dev Biol Ctr, Bethesda, MD 20892 USA
[2] NIDDK, Mammalian Dev Biol Sect, Bethesda, MD 20892 USA
[3] NHLBI, Lab Mol Physiol, Bethesda, MD 20892 USA
[4] Duke Univ, Dept Med, Div Med Oncol, Durham, NC USA
[5] NHLBI, Electron Microscopy Core, Bethesda, MD 20892 USA