[1] Univ Iowa, Carver Coll Med, Dept Anat & Cell Biol, Iowa City, IA USA
[2] Univ N Carolina, Lineberger Comprehens Canc Ctr, Chapel Hill, NC 27599 USA
[3] Univ N Carolina, Dept Biol, Chapel Hill, NC USA
[4] Univ Iowa, Dept Epidemiol, Coll Publ Hlth, Iowa City, IA USA
[5] Univ N Carolina, Dept Genet, Chapel Hill, NC USA