Modelling microtubule-motor interactions in self-organized acentrosomal spindle assembly and the effect of nucleation and GTP-hydrolysis on filament length

Abstract

Microtubules (MTs) with the help of motors self-organize into bipolar spindle structures. Spindles are essential for the proper segregation of genetic material into daughter cells. Plants and many oocytes lack centrosomes, which are the main MTOC in animal cells. While several studies have addressed the mechanisms of acentrosomal spindle assembly, the models are too simple and lack the attributes of an in-vivo scenario. In this report, we describe two aspects that relate to plant spindle assembly. We address the more general question of the minimal model components required to generate a bipolar spindle. Next, we have attempted to address the distribution of lengths governed by nucleation and GTP-hydrolysis of microtubules. Here, we examine the role of motors in the self-organization of bipolar spindle using computational models. A previous computational model of static MTs with effective motors showing bipolarization (Schaffner and José (2006)) was reproduced with bipolar structures but not as focussed as in the paper. However, this model has many shortcomings, which we attempted to address by adding dynamic MTs and other motors and components and have promising results that could help understand the system better and provide experimental tests. Our results show that, in a minimal system, motors affect the orientation and organization of MTs. A self-organized multi-polar spindle structure is formed, which becomes more robust on adding augmin nucleators. The system needs to be optimized with other experimental considerations to achieve self-organized bipolar spindles. GTP-hydrolysis rates govern the MT lengths and dynamics.