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BP: Fachverband Biologische Physik

BP 6: Cytoskeletal Filaments I

BP 6.2: Talk

Monday, March 12, 2018, 15:15–15:30, H 1058

The mitotic spindle is chiral due to torques generated by motor proteins — •Maja Novak¹, Bruno Polak², Juraj Simunic², Zvonimir Boban¹, Andreas W. Thomae³, Iva M. Tolic², and Nenad Pavin¹ — ¹Faculty of Science, University of Zagreb, Zagreb, Croatia — ²Rudjer Boskovic Institute, Zagreb, Croatia — ³University of Munich, Munich, Germany

Mitosis relies on forces generated in the spindle, a micro-machine composed of microtubules and associated proteins. Forces are required for the congression of chromosomes to the metaphase plate and their separation in anaphase. However, torques may also exist in the spindle, yet they have not been investigated. Here we show that the spindle is chiral. Chirality is evident from the finding that microtubule bundles follow a left-handed helical path, which cannot be explained by forces but rather by torques acting in the bundles. STED super-resolution and confocal microscopy of human spindles revealed that the average helicity of the bundles with respect to the spindle axis is about -2°/μm. Inactivation of kinesin-5 (Kif11/Eg5) abolished the chirality of the spindle. We introduce a theoretical model, which predicts that torques generate curved shapes of bundles, where the twisting component of the torque is required for the helical component of the shape. By comparing the model with experiments, we find that the twisting moment is roughly -10 pNμm. We conclude that torques generated by motor proteins, in addition to forces, exist in the spindle and determine its architecture.

Reference: bioRxiv 167437, https://doi.org/10.1101/167437