Fig. 3: Simulations predict that growth stagnation of a single protofilament leads to extended microtubule pausing.

A Schematic of simulation: a growing microtubule (left) has a single protofilament randomly targeted for growth stagnation (center). The remainder of the protofilaments continue growing, leaving behind the targeted, stalled protofilament (right). Growth stalling of a single protofilament increases the difference in length between the longest and the shortest protofilament at the tip, termed “Tip Extension Length” (black arrows). B Left: A representative trace showing simulated microtubule length vs. time. The time point at which an estradiol–tubulin complex was incorporated into the tip of a single protofilament (T_{incorporation}) is noted in the trace (black vertical line). Right: Quantification of the simulated pre- and post-incorporation microtubule growth rate. C Left: A representative simulation trace showing the longest (green) and shortest (red) protofilament pre- and post-incorporation. The tip extension length is denoted with the purple arrow. Right: Quantification of simulated microtubule tip extension length pre- and post-single protofilament targeting. D TEM images of growing microtubule tip extensions in control (left), and estradiol (center) conditions. Lines on the lower images indicate the measurement of the longest protofilament (orange) and shortest protofilament (yellow), used to determine extension length. Right: Quantification of tip extension lengths on growing microtubules (error bars: mean ± SEM). E Left-Top: Live cell images of microtubules in a control and estradiol-treated LLC-Pk1 cell with the measured microtubule tip delineated with yellow lines. Left-bottom: MATLAB readout of the Gaussian survival curve (blue) showing a single microtubule tip extension trace for control (bottom left) and estradiol-treated (bottom right). Right: Quantification of the tip standard deviation across treatment groups (error bars: mean ± SEM).