Supplemental Data

Files in this Data Supplement:

• Supplemental Table 1
• Supplemental Figure 1 - Microtubule zippering and catastrophic collisions in YFP-TUA6-expressing cells. These panels show the outcome of shallow-angle and steep-angle encounters between cortical microtubules in YFP-TUA6-expressing cells. The microtubule of interest is marked by an asterisk, and the arrows denote the onset of microtubule polymerization or depolymerization. The numbers denote time in seconds. (A) A growing cortical microtubule has a shallow-angle (28^o) encounter with a pre-existing microtubule at 15 s (z) and aligns itself with the pre-existing microtubule. Note the long contact time (at least 130 s) between these microtubules. (B) A growing cortical microtubule has a steep-angle (65^o) encounter with a pre-existing microtubule at 10 s (c) and depolymerizes after about 10 s of contact time. Scale bars = 1 μm.
• Supplemental Figure 2 - Monte Carlo modeling using identical zippering constraints for transverse and longitudinal microtubules. The dynamic behavior of interphase cortical microtubules was simulated starting with the same microtubule configuration as in Figure 5. These ?microtubules? were subjected to an iterative Monte Carlo modeling technique, based on the parameters defining the stochastic dynamics of individual cortical microtubules, and the rules of modification of these parameters, based on microtubule encounter angles. In this case, both transverse and longitudinal zippering microtubules were constrained from shrinking for one iteration. Each iteration represents a span of 1 min. The starting condition shows the initial distribution of the microtubule angles. By iteration 7, it is apparent that some microtubule orientations (e.g., 0-15^o and 76-90^o) are not favored and that these microtubules are selectively depolymerized. In contrast, other microtubule orientations (46-60^o) are selectively stabilized as a result of zippering and persist over time. By iteration 10, a predominant microtubule orientation (46-60^o) is clearly established, reflecting a local, parallel microtubule organization. Therefore, the difference in zippering constraint between transverse and longitudinal microtubules is not required for the generation of parallel microtubule organization in the present model.
• Supplemental Figure 3 - Monte Carlo modeling using only microtubule zippering to modify the behavior of the simulated microtubules. The dynamic behavior of interphase cortical microtubules was simulated starting with the same microtubule configuration as in Figure 5. These ?microtubules? were subjected to an iterative Monte Carlo modeling technique, based on the parameters defining the stochastic dynamics of individual cortical microtubules and their modification upon microtubule zippering. Catastrophic collisions were not modeled in this instance. Each iteration represents a span of 1 min. The starting condition shows the initial distribution of the microtubule angles. By iteration 7, there is no appreciable microtubule organization and the microtubules remain disorganized by iteration 10. Therefore, microtubule zippering alone does not give rise to a parallel microtubule organization.
• Supplemental Figure 4 - Monte Carlo modeling using only catastrophic collisions to modify the behavior of the simulated microtubules. The dynamic behavior of interphase cortical microtubules was simulated starting with the same microtubule configuration as in Figure 5. These ?microtubules? were subjected to an iterative Monte Carlo modeling technique, based on the parameters defining the stochastic dynamics of individual cortical microtubules, and their modification upon catastrophic collisions. Microtubule zippering was not modeled in this instance. Each iteration represents a span of 1 min. The starting condition shows the initial distribution of the microtubule angles. By iteration 7, the bulk of the discordant microtubules have been lost and there is the hint of a predominant microtubule orientation (46-60^o). However, this does not resolve into a clear microtubule organization by iteration 10. Therefore, catastrophic collisions alone do not give rise to a parallel microtubule organization.
• Supplemental Movie 1 - Cortical microtubule dynamics in MBD-DsRed-expressing cells. The interphase cortical microtubules are predominantly transverse with respect to the elongation axis of the cell. Note the dynamic behavior of the individual microtubule ends. This movie was compiled from time-lapse images captured from an MBD-DsRed-expressing cell and has been sped up about 100-fold.
• Supplemental Movie 2 - Monte Carlo simulation of microtubule dynamics using the constraints imposed by microtubule interactions. The individual simulated microtubules are color coded for ease of identification. Note that microtubule encounters result in microtubule bundling, microtubule reorientation, and the emergence of local microtubule order.
• Supplemental Movie 3 - Monte Carlo simulation of microtubule dynamics in the absence of constraints imposed by microtubule encounters. The individual simulated microtubules are color coded for ease of identification. Note that the microtubule dynamics are determined purely by stochastic processes and that the microtubules remain randomly arranged in the absence of the effect of microtubule encounters.
• Supplemental Movie 4 - Monte Carlo simulation of the dynamics of short microtubules. The short length of these simulated microtubules does not allow any microtubule encounters, and therefore the dynamics of the microtubules are solely stochastic in nature and the microtubules remain randomly arranged.