Figure 2. Astral and Spindle Microtubule Dynamics Vary with Cell Volume During C. elegans Embryo Cleavage.

(A) Still frames from live 2-photon imaging of C. elegans embryos expressing a GFP-tagged plasma membrane probe (Pleckstrin Homology (PH) domain) during the first five embryonic divisions (1- to 16-cell stage). Images correspond to maximal projections of z-stacks covering the entire thickness of the embryo. Scale bar, 20 μm. Blastomere names are indicated except for the 16-cell stage. At the 8-cell stage, progeny of AB and P1 were grouped together as ABxx and P1xx respectively.

(B) Mean astral (green) and spindle (red) microtubule dynamics parameters: mean microtubule growth rate, catastrophe frequency, shrinkage rate and rescue frequency (from Figure 1C) for each type of blastomere plotted over the corresponding average cell volumes (from Figure S1). Key for different blastomeres shown in the top box. Dotted lines correspond to the linear regression curves. Pearson correlation coefficient (r²) is indicated at the top of each graph if p ≤ 0.01 (no corr. is indicated otherwise).

(C) From left to right, still images from confocal live imaging of C. elegans control one-cell embryo, control 2-cell embryo, thermosensitive (ts) mutant embryo of the formin cyk-1 at the ‘2-cell’ stage after P0 cytokinesis failure and abnormally large C27D9.1(RNAi)-treated embryo. All express GFP-tagged β-tubulin. Corresponding schematics with color-coding for spindle microtubules in different conditions shown at the bottom. Scale bar, 20 μm.

(D) Spindle microtubule growth rates measured at 25°C (restrictive temperature for the cyk-1(ts) mutant) for the indicated conditions. Color-coding for the different conditions corresponds to the schematics in (C). (Error bars, SD; one-way ANOVA with Dunnett’s multiple comparisons test, **: p≤0.01, n.s.: p>0.05).