Fig. 4: Friction of bulky cargo bound to dynein against a viscous cytoplasm generates the anaphase flows.
From: Cytoplasmic flow is a cell size sensor that scales anaphase
a, Snapshots of a metaphase cell, showing mitochondria (top) and an overlay of Mito-GFP (colour coded by intensity) and α-tubulin-ATTO-565 (white) (bottom). Dashed box, FRAP area, near the aster. b, Left: time projection of mitochondria during anaphase. Dashed yellow box, FRAP area; grey circle with asterisk, aster. Scale bar, 10 µm. Right: kymograph of the track in the blue box showing a fast followed by a slow episode. Scale bar, 1 µm. c, Mitochondria track in anaphase colour coded by velocity. Asterisk, beginning of the track. Note the transition from fast (red) to slow (blue) velocities. d, Weighted mean square displacement analysis of mitochondria tracks as a function of delay (n = 68 tracks from 6 embryos and the 4-cell stage). Blue line, fast episodes; orange line, slow episodes. e, Schematics of the trajectories of mitochondria, highlighting fast episodes (blue line; blue dot indicates mitochondria bound to dynein) and slow episodes (orange line; orange dot indicates mitochondria moved by the flows). Astral microtubules, grey; plus and minus, microtubule polarity; [0,0], centre of the aster. f, Individual tracks of mitochondria from a single cell in anaphase. Fast episodes (continuous line) are radial, while slow episodes (dashed line) have the direction of the flows (orange arrow). Colour code, time. g, Time projection of mitochondria and chromosomes. h, PIV analysis of the cell in g. Arrows, flow field; colour code, flow velocity; grey mask, chromosomes. i, Time projection of mitochondria and chromosomes after dynein inhibition. j, PIV analysis of the cell in i. Arrows, flow field; colour code, flow velocity; grey mask, chromosomes. The flow pattern is absent. Scale bars, 50 µm. k,l, Chromosome velocity in control and dynein inhibition in anaphase A (k; control, n = 19 embryos; p150, n = 4 embryos) and anaphase B (l; control, n = 27 embryos; p150, n = 8 embryos; P = 2 × 10−5). m, Number of mitochondria tracks per minute (control, n = 5 embryos; p150, n = 8 embryos). n, Flow vorticity (control, n = 22 PIV measurements; p150, n = 16 PIV measurements; for each cell, there can be up to two vorticity measurements corresponding to the sets of segregating chromosomes in the dividing cell). Statistical significance was determined by two-tailed Mann–Whitney test. The error bars represent s.e.m. n.s., not significant.
