Simulating self-organization of the cortical microtubule cytoskeleton

We are developing computer simulations and analytical models, in collaboration with Drs. Gautam and Deshmukh at Texas A&M, to study the mechanisms underlying the self-organization of cortical microtubules into ordered patterns.

Cortical microtubules are highly dynamic and are typically tightly attached to the plasma membrane. As a result, individual microtubules frequently physically run into each other during their life times. We have previously shown that the contact angle between two encountering microtubules strongly biases the outcome of such interactions. Shallow-angle interactions typically lead to microtubule bundling (zippering), whereas, steep-angle interactions either lead to microtubule depolymerization (catastrophic collision) or cross over. We have proposed that these simple interactions lead to self-organization of cortical microtubules. To examine how organization develops from a particular configuration of participants and conditions, we are developing computer simulations and analytical models based on experimental data obtained from Arabidopsis plants. These models will be tested using data collected from mutant Arabidopsis plants that have abnormal cortical microtubule organization.

 

Snapshot of microtubule organization (A, D), distribution of microtubule angles (B, E) and entropy plots (C, F) from computer simulations using microtubule dynamics obtained from wild-type plants either including cortical microtubule interactions (top row) or ignoring the interactions between cortical microtubules (D, E and F). The smooth decline in entropy over time indicates increasing array organization when cortical microtubule interactions are accounted for. In contrast, the microtubules fail to become organized (entropy doesn't drop) if interactions between cortical microtubules are ignored.

Examples of different cortical microtubule interactions in Arabidopsis plants. (A) Bundling after shallow-angle encounter (B) Catastrophe after steep-angle encounters (C) Crossover and severing after steep-angle encounters. The yellow arrow-heads mark the microtubule of interest in each case.