Skip to main content
. 2020 Jul 9;9:e54930. doi: 10.7554/eLife.54930

Figure 3. Chiral counter-rotating flows are cell-lineage dependent.

(A) Possible mechanisms of spindle skew and cell rearrangement. Hypothesis one: spindle skews are driven by spindle elongation. The mitotic spindle initially elongates along the dorsoventral axis (a’ and b’), but then skews (c’) because there is not enough space given the physical constraints imposed by the eggshell. Dashed line depicts the cell division axis, red dots depict spindle poles, arrows indicate spindle pole movements. Hypothesis two: spindle skews are driven by counter-rotating flows of the dividing cell halves. Left: top view, right: side view. Chiral counter-rotation of the two halves of a dividing cell gives rise to a cell skew if the dividing cell experiences non-uniform friction with its surroundings, e.g. a lower friction with the eggshell above and a higher friction with the cell below. (B) Representative images of cortical myosin (grey, NMY-2::GFP) for the second and the third cell division of C. elegans embryos. Arrows indicate the cortical flow field as measured by PIV and time-averaged over 21 s and over the onset of cytokinesis. Arrow colors indicate the y-direction velocity (parallel to the cytokinesis furrow, coordinate systems are indicated). (C) Histograms of the instantaneous chiral counter-rotating flow velocity vc for par perturbations (see Materials and methods for definition). Solid lines indicate the best-fit gaussian probability density function. Dotted vertical colored lines represent the mean vc, grey boxes represent the error of the mean. Thin black solid lines indicate a chiral flow velocity of zero. Inset, colored cells indicate the cell analyzed; AB lineage in blue, P/EMS lineage in orange. (D) Spindle skew angle for control (L4440), par-2; chin-1; lgl-1 (RNAi) and par-6 (RNAi) embryos. (E, F) Schematic of a C. elegans embryo. 3-D recordings capturing spindle pole movements and corresponding spindle skews were projected on either the (E) anteroposterior-dorsoventral (AP-DV) plane (red) or the (F) left-right-dorsoventral (LR-DV) plane (blue). (G, H) Spindle skew angles during the second and third cell division in control (G) and upon par-2 (RNAi) (H) projected onto the anteroposterior-dorsoventral plane (termed AP-DV plane, left) or onto the dorsoventral-left-right plane (termed LR-DV plane, right). The embryo schematic denotes the plane of projection (rectangle) and the direction of view (arrow) as described above. Scale bars, 10 µm. Errors indicate the error of the mean at 95% confidence.

Figure 3.

Figure 3—figure supplement 1. 3-D spindle skew dynamics in the AB cell and the P1 cell.

Figure 3—figure supplement 1.

(A) Top panels: schematics of a C. elegans embryo with the anteroposterior-dorsoventral (AP-DV) projection plane (red) and the left-right-dorsoventral (LR-DV) projection plane (blue) indicated. Arrows indicate the direction of the projection. Bottom panels: Schematics of a two cell embryo projected onto the AP-DV plane (red) or LR-DV plane (blue) with the spindle skew indicated. The dotted grey line marks the initial cell division axis and the dotted black line marks the final cell division axis. Arrows indicate the direction of spindle pole (red circles) movements during cytokinesis. (B) Representative fluorescence images of a two cell embryo expressing a tubulin marker (TBB-2::mCherry) at anaphase onset (top) and at the end of cytokinesis (bottom) in mildly compressed embryos mounted using the agar pad method. Left panels show projections onto the left-right-dorsoventral plane (denoted LR-DV), and right panels show projections onto the anteroposterior-dorsoventral plane (denoted AP-DV). (C) Representative fluorescence images of a two-cell embryo expressing TBB-2::mCherry undergoing AB cell division in uncompressed embryos mounted by embedding in low-melt agarose. Projections as in (A). (D) Representative florescence images of three cell embryo expressing TBB2::mCherry undergoing P1 cell division in uncompressed embryos mounted using low-melt agar method. Projections as in (A). Scale bar 10 µm. Embryo schematic denotes the plane of projection marked by the rectangle and arrow indicates the direction of view.
Figure 3—figure supplement 2. 3-D Spindle skew dynamics in par-2 (RNAi) embryos.

Figure 3—figure supplement 2.

(A) Representative fluorescence images of a two-cell embryo expressing TBB2::mCherry upon par-2(RNAi) undergoing cell division mounted by embedding in low-melt agarose. Left panels show projections onto the dorsoventral-left-right plane, middle panels show projections onto the anteroposterior-dorsoventral plane and right panels show projections onto the dorsoventral-right-left plane. Note that right and left panels are both viewing along the anteroposterior axis but in opposite directions. Scale bar 10 µm. Embryo schematic denotes the plane of projection marked by the rectangle and arrow indicates the direction of view.