Table 1. Parameters used in simulations.
| Parameter | Value | Remark |
|---|---|---|
| One simulation step | 0.1 s | Estimated from in vivo cap growth (Jiang and Harris, 2019) |
| One pixel | 0.1 micron | Estimated from in vivo cap growth (Jiang and Harris, 2019) |
| Actomyosin network | ||
| Myosin node density (Den_m) | Varied (0–1) | Proportion of total pixels in the actomyosin zone with a myosin node |
| Myosin node activity (M) | Varied (0–1) | Relative activities |
| Search radius for establishing connections with surrounding myosin nodes (Dthres) | five pixels | Based on optimal actin filament length for cortical actomyosin contractility (Chugh et al., 2017) |
| Maximum number of connections with surrounding myosin nodes (MaxNeigh) | 6 | Optimized* |
| Maximum number of myosin nodes per pixel (Nmax) | 20 | Optimized* |
| Coefficient of myosin force (Kmyosin) | 0.5 nN | Order of magnitude measured for myosin force (Finer et al., 1994) |
| Coefficient of spring force (Kspring) | 0.05 nN/nm | Order of magnitude measured for actin elasticity (Kojima et al., 1994) |
| Node-node connection resting length (lo) | Variable | Mean length of all connections before a simulation starts |
| Arp2/3 network | ||
| Initial nucleation site density (Den_c) | 0.1 and 0.01‡ | Proportion of total pixels in the nucleation zone with a nucleation site† |
| Actin polymerization force coefficient (Kpoly) | 0.5 nN | Order of magnitude measured for Arp2/3 networks with same area (Bieling et al., 2016)† |
| Age of plus end node when a branch is induced (AgeBr) | nine steps | Optimized* |
| Maximum length between nucleation site and plus end node (Lth) | 20 pixels | Ordered of magnitude calculated for capped actin filaments (Schafer et al., 1996) |
| Minimum age of plus end node when its loss becomes possible (Ageth) | 20 steps | Optimized* |
| Probability of loss of plus end node at each step (Pdel) | 0.7 | Optimized* |
| Network-network Interface | ||
| Radius around a node’s initial position to identify potentially interacting nodes of the other network (SR) | five pixels | Assumed‡ |
| Radius around a node’s target position to determine if nodes of the other network are absent, which allows the move (Vex) | two pixels | Assumed‡ |
*Optimized in relation to other parameters of the actomyosin or Arp2/3 model (see Model Formulation for details).
†These parameters of the Arp2/3 model were coarsened to account for a plus end node representing only one actin filament whereas a myosin node represents a myosin mini-filament connected to many actin filaments. To increase the impact of each plus end node relative to a myosin node, the initial actin nucleation site density was set on the lower side whereas the polymerization force of a single plus end node was set on the higher side.
‡See Model Formulation for details.