Fig. 1: Microtubule dynamics, molecular motors and tip trackers stabilize bipolar organization of two microtubule asters.

a Schematics of the double optical trap artificial spindle assay. Microtubule seeds are tethered to plastic beads that are held in two optical traps and capped at their minus ends to mimic two microtubule organization centers. The assay measures the force acting between asters. b Example recording shows pulling force (top) and the corresponding decrease in distance between the beads (bottom) in the presence of HSET only. Maximum force inferred from traces is shown. c Example recording shows pushing force (top) and the increase in the distance between beads (bottom) in the presence of EB3 and HSET. d Example recording of a balance trace with no force generated while microtubules are engaged in the presence of EB3 and HSET. In b–d light blue are original data and dark blue is smoothed with 100 point moving average. e Histograms of maximum pulling and pushing forces extracted from individual traces. Bars show mean values and whiskers standard deviation. Number of measurements (left to right): n = 24, n = 20, n = 0 (no events detected), n = 19. f Quantification of the fraction of time that the system spends pushing, pulling, and being balanced (with at least two antiparallel microtubules from the opposite asters engaged) or disengaged (when microtubules from opposite asters do not interact) depending on the experimental conditions (n = 84 total traces). Source data for this figure are provided as a Source Data file.