Fig. 3.
Asymmetric distribution of pSmad1GSK3, pSmad1MAPK, p-β-catenin, and total polyubiquitinylated proteins in synchronized Cos7 daughter cells. (A and B) Asymmetric pSmad1GSK3 at early daughter cell stage. (C and D) Asymmetric pSmad1MAPK after cell division. Note that γ-tubulin (red dots) is equally partitioned (arrowheads), whereas pSmad1MAPK accumulates asymmetrically in the nuclear bay cytoplasm of one cell (arrow); these daughter cells are still joined by the midbody (mb). The z-stacks (shown as Insets at the top of A and C) show that the merged images include the entire cell. (E and F) β-Catenin phosphorylated by GSK3 and total polyubiquitinylated proteins are asymmetrically inherited and accumulate in nuclear bays. Note that the nuclear bays are also asymmetrical. (G and H) Cos7 daughter cells with asymmetric pericentrosomal pSmad1GSK3 respond to BMP7 treatment (5 nM for 90 min) by translocating equal levels of pSmadCter into the nucleus (see Fig. S3 for experimental details). (I and J) Clones of eight Cos7 cells cultured for 48 h after synchronization reveal successive asymmetric divisions of pSmad1GSK3 and pSmad1MAPK through three consecutive cell cycles. (Insets) Low-power images demonstrating that asymmetric cells indeed derive from isolated clones. (Scale bar: 10 μm.)