Modelling and image processing of microtubule dynamics and organisation

• Main Author: Rookyard, Chris
• Published: University of East Anglia 2014
• Subjects: 004
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.681507

Microtubules, dynamic protein polymers, form networks that are essential for intracellular organisation. Involved in many cellular processes that are vital in development and homeostasis, improper regulation of the microtubule network is implicated in various diseases. This work addresses the relationships between microtubule dynamics and organisation, using image processing and modelling, focussing on two features of microtubule organisation: radiality and alignment. The hypothesis that radiality results from modulation of dynamics at the cell periphery was tested. Firstly, cells in which the small GTPase Rac1 was inhibited were used as a model for perturbed radiality. Measurements of microtubule dynamics in central and peripheral regions showed that Rac1 inhibition alters microtubule dynamics and the orientation of their growth at the cell periphery. Further investigation was carried out with a simple 1-dimensional, two-area dynamics model, which confirmed that a two-area dynamics system is sufficient to target microtubules to a given length. The propensity to grow of any given dynamics parameters is a major determinant of the accuracy of length targeting, while the extent of pausing and the average length have a modulatory effect on accuracy. Simulation of measured dynamics indicated that two-area dynamics may contribute to radiality in reality, but that this mechanism may work in concert with other cortex-specific processes. The alignment of microtubules was quantified with a new application of the Fourier transform. Depletion of +TIP protein EB2 produced highlyaligned microtubules, and inhibition of formins rescued this phenotype. Inhibition of Rac1 produced less-aligned microtubules in otherwise unperturbed cells, while in EB2-depleted cells, microtubules were further aligned. The method was also used to quantify alignment in plant microtubule arrays. This work presents a set of analyses that test ideas as to how the microtubule network is organised, and highlight interesting relationships between dynamics and organisation that will yield exciting future investigation.