1. Department of Cell and Development Biology (J.S., C.W.A., R.G., K.M.R., M.L.I.-A.), Northwestern University, Chicago.
2. Molecular Biology Institute (G.E.H., F.M.), University of California, Los Angeles.
3. Department of Molecular, Cell and Development Biology (M.P.), University of California, Los Angeles.
4. Department of Medicine, Feinberg School of Medicine (K.M.R.), Northwestern University, Chicago.