Extended Data Fig. 1: Orientation terminology, image analysis and centrosome motion quantification.

a, The configuration and the terminology of embryo orientation used in this study. The mitotic spindle is simply illustrated by the green dumbbell, while astral MTs illustrated by slender green sticks. The confocal imaging plane, which is parallel to the coverslip, is defined as the x-y plane, with the z = 0 plane falling at the centre of the spindle or the PNC. The embryo’s A–P direction is assigned as the longitudinal direction (x axis), with the embryo’s posterior end facing the positive x direction. And the transverse direction refers to the y direction. b,c, An example of the centrosome-tracking image. b, The two-colour merged image of an C. elegans embryo expressing mCherry-tagged γ-tubulin (red) and GFP-tagged β-tubulin (green). The two separate images of the dashed-line region are shown in the right panel. The upper one is a γ-tubulin-labeling image with its labeled centrosome locations derived by MATLAB Particle Tracking Code Repository by Daniel Blair and Eric Dufresne. The lower one is a β-tubulin-labeling image, while its centrosome information is derived from the particle tracking code plus the second-step correlation method. c, Top, the square image patch with the artificial ring structure mimicking a centrosome. Bottom, an example of the post-processed (background-subtraction and thresholding) β-tubulin-labeling image used for correlation calculation. (The top and bottom images are displayed on the same scale.) d,e, The information of the embryo long axis (or longitudinal direction) can be extracted automatically in two ways: d, through linear fitting on the trajectory data of the anterior and posterior centrosomes, or e, through fitting the automatic detected embryo contour with a simple ellipse. f, An example of the automatic detected embryo contour and the embryo anterior/posterior ends. g, An example of oscillation peak detection. The crests/troughs (or the peak points) of the transverse oscillations were calculated by (1) first finding the local maxima/minima from the smoothed amplitude data, and then (2) fitting the raw amplitude data, which fall within the 15-second windows around the above detected maxima/minima, by Gaussian function (see the enlargements). The derived peak points are marked by pink asterisks. All scale bars on images are 10 μm.