Figure 6. Palmitoylation levels of importin α modulate nuclear scaling in vivo.

(A) Schematic showing the known values for cell size and total importin α concentration during X. laevis development and the predicted cytoplasmic concentrations of importin α at various stages during development. Right panel: Graph of the predicted decrease in cytoplasmic importin α concentrations due to its progressive sequestration at the plasma membrane as the surface area/volume ratio increases during embryogenesis.

(B) Left panel: Fluorescence images of importin α localization and histone H2B to label nuclei in embryos at stage 7 following injection of DMSO, palmostatin or Wnt-C59 into the zygote. Palmostatin increased, and Wnt-C59 decreased the ratio of importin α at the cell periphery compared to the cell interior see Figure S2E for quantification. Right panel: Mean intensity ratio of importin α at the cell membrane compared to the cell center in embryos at stage 7 that had been injected with DMSO, palmostatin, or Wnt-C59. Mean ± SD from 30 cells, p < 0.005. Scale bar, 10 μm.

(C) Plot of nuclear diameters at different cell diameters following drug or vehicle injection. Palmostatin treatment led to earlier onset of nuclear scaling, while Wnt-C59 inhibited nuclear scaling. (p < 0.05). P-values indicate statistical difference between y-intercepts of regression lines from 3 experiments, calculated using an analysis of covariance.

(D) Plot of nuclear diameters at different cell diameters upon co-injection of palmostatin with wild type or non-palmitoylated importin α. Importin α-wt did not reverse the nuclear size decrease, while importin α-NP increased nuclear size and abrogated the effects of palmostatin. (p < .05). P-values indicate statistical difference between y-intercepts of regression lines from 3 experiments, calculated using an analysis of covariance.