Tuning Microtubule-Actin crosstalk to control Mitotic Fidelity

有丝分裂的准确进行对于正确的染色体分离、维持染色体的稳定性和整倍体是至关重要的。在我们之前与Linda Wordeman(美国西雅图)和Holger Bastians(德国哥廷根)的实验室合作的工作中，我们已经证明有丝分裂中微管动力学增加是一个关键缺陷，例如在包括癌症在内的人类病理中可以看到，它直接触发染色体错误分离和非整倍体。然而，目前尚不清楚微管动力学增加是如何导致整个染色体错误分离的。在我们最新的前期工作中，我们发现，即使微管动力学的微小变化也会对有丝分裂纺锤体的正确定位产生重大影响，这涉及到有丝分裂皮质肌动蛋白组织的放松调控。事实上，我们发现微管生长的增加可以导致关键的肌动蛋白组织者RAC1的非计划激活，而RAC1被认为是通过激活Arp2/3肌动蛋白核仁来触发分支肌动蛋白聚合。此外，我们发现微管动力学增加对皮质肌动蛋白张力的影响可能是通过非计划的RAC1-Arp2/3激活而介导的，并导致纺锤体错误定位和整个染色体错误分离。基于这些新的和意想不到的发现，我们假设微管动力学增加在有丝分裂中触发RAC1-Arp2/3的意外过度激活，以改变皮质肌动蛋白组织，从而降低皮质张力，从而影响纺锤体的早期定位，并导致染色体错误分离。在我们计划的项目中，我们将以Wordeman和Bastians实验室的互补专业知识为基础，研究微管依赖的RAC1激活的机制，非计划的RAC1-Arp2/3激活对有丝分裂皮质组织和张力的影响，以及纺锤体错误定位和染色体错误分离的机制，以响应微管动力学增加和有丝分裂肌动蛋白皮质组织的解除调节。我们将研究人类体细胞中的微管-肌动蛋白串扰，并将我们的发现转移到包括棘皮动物和斑马鱼在内的胚胎系统中。通过这一点，我们的研究将解决微管和肌动蛋白细胞骨架在有丝分裂中的重要和鲜为人知的串扰机制，这与适当的染色体分离高度相关。

Accurate execution of mitosis is pivotal for proper chromosome segregation, the maintenance of chromosomal stability and euploidy. In our previous collaborative work of the lab of Linda Wordeman (Seattle, USA) and Holger Bastians (Göttingen, Germany) we have shown that increased microtubule dynamics in mitosis is a key defect, e.g. seen in human pathologies including cancer, that directly triggers chromosome missegregation and aneuploidy. However, it is unknown how increased microtubule dynamics causes whole chromosome missegregation. In our most recent preliminary work we discovered that even small changes in microtubule dynamics have a significant impact on the proper positioning of the mitotic spindle and this involves a deregulation of the mitotic cortical actin organization. In fact, we found that increased microtubule growth can lead to unscheduled activation of the key actin organizers RAC1 that are known to trigger branched actin polymerization via activation of Arp2/3 actin nucleators. Moreover, we found that increased microtubule dynamics impacts on cortical actin tension that might be mediated by unscheduled RAC1-Arp2/3 activation and leading to spindle mispositioning and whole chromosome missegregation. Based on these new and unexpected findings we hypothesize that increased microtubule dynamics triggers unscheduled hyper-activation of RAC1-Arp2/3 in mitosis to alter cortical actin organization that lowers cortex tension, thereby influencing early spindle positioning and causing chromosome missegregation. For our planned project we will build on the complementary expertise of the Wordeman and Bastians labs to investigate the mechanisms of microtubule dependent RAC1 activation, the impact of unscheduled RAC1-Arp2/3 activation on mitotic cortex organization and tension and the mechanisms of spindle mispositioning and chromosome missegregation in response to increased microtubule dynamics and deregulated mitotic actin cortex organization. We will investigate the microtubule-actin crosstalks in human somatic cells and we will transfer our findings into embryonic systems including Echinoderms and Zebrafish. With this, our studies will address the important and little understood cross-talk mechanisms of the microtubule and actin cytoskeleton in mitosis, which are highly relevant for proper chromosome segregation.