Collective Mechanics of Dynein Driven Microtubule (MT) Transport, Oscillations and Bead Motility

Abstract

Dynein is a crucial ATP-driven motor protein involved in processes like spindle assembly, vesicle transport, organelle positioning, and ciliary beating. This study explores dynein’s collective behavior in microtubule (MT) transport, oscillations, and organelle motility. In Saccharomyces cerevisiae, mitosis is closed and requires dynein to asymmetrically position the nucleus by pulling MTs nucleated from the spindle pole body (SPB). Image analysis of MT-cortex contacts during mitosis showed that the bud cell’s MTs had more frequent and longer contacts with the bud cortex than the mother cell, suggesting a role for dynein in nuclear positioning. Previous in vitro studies with full length cytoplasmic dynein indicated that increasing the number of dynein enhances the speed of MT, but the mechanisms behind the motor cooperativity in truncated motors remains to be explored. In this study, gliding assays with truncated yeast dynein at varying motor densities were reconstituted revealing that even minimal motor numbers influenced MT velocity. The MT velocity increases and saturates rapidly as the motor number increases prompting new models to explain motor cooperativity on the basis of single molecular behavior of the motor. Unusual MT patterns, including oscillations and spirals, have been observed in gliding assays. Single MT oscillations were reconstituted in modified assays by clamping the MT plus ends in a dynein gliding assay. The oscillations showed dependence on MT length and motor density, highlighting the role of geometry, MT buckling, and collective motor activity in emergence of single MT oscillations. This minimal in vitro set up can be used in future to study the role of MT-motor mechanics in flagellar beating. In assays with pinned MTs, MT spirals were studied, revealing that spiral radius scaled di!erently from acto-myosin systems. The scaling of spiral radius with the MT length was explained on the basis of length dependent persistence model of the MT. This is suggestive of anisotropic nature of MT. This work also explored cargo transport through in vitro assays with purified motors and synthetic cargo. This set up can be extended to study bidirectional transport with synthetic cargoes or organelles. Collaborative e!orts, taxol-stabilized MTs were tested as marker for rotational movement. Overall, these findings reveal self-organized transport dynamics arising from the collective properties of dynein, providing a deeper understanding of motor-motor and MT-motor coordination in various cellular processes.