An investigation of factors that regulate cytoskeleton in the first mitotic division of the C. elegans embryo

• First mitosis in C. elegans embryo

• Author / Creator

  Bajaj, Megha

• Microtubule dynamics is regulated by naturally occurring microtubule-associated proteins occurring in the cellular environment as well as by natural and synthetic compounds. These compounds target the microtubule cytoskeleton and serve as anti-mitotic drugs. Therefore, microtubules continue to be one of the most effective targets for developing new anti-mitotic agents. Laulimalide is one such anti-mitotic agent that was isolated from the marine sponge, Cacospongia mycofijiensis. Laulimalide has been shown to disrupt microtubules in a manner similar to paclitaxel, by causing bundling of microtubules and inducing microtubule stabilization. However, the acute effects of laulimalide on microtubules and its mode of action are unclear. The C. elegans embryo is an excellent model to characterize microtubule-targeted drugs, and herein, I report the first analysis of laulimalide in this system. My work indicates that laulimalide induces a concentration-dependent, biphasic change in microtubule polymer dynamics in the embryo. This analysis provides novel information about the acute in vivo effects of laulimalide on the microtubule polymer and helps distinguish this anti-mitotic drug from the widely-used chemotherapeutic paclitaxel. In the C. elegans embryo, CYK-1 formin is required for a late step in cytokinesis. Based on the localization of CYK-1, it has been proposed to function in cytokinesis by bridging microtubules and microfilaments at the cleavage furrow. This bridging role of CYK-1 could stabilize the cytokinetic cleavage furrow by binding to spindle microtubules at the mid-zone on one side and actin, which is associated with the plasma membrane, on the other side. CYK-1 has also been implicated in cortical functions prior to cytokinesis, suggesting that it has a more global role in regulating the actin cytoskeleton. Using live-cell imaging and reverse-genetics, I found that depletion of CYK-1 resulted in exaggerated spindle pole oscillations during anaphase in the one-cell C. elegans embryo, suggesting that CYK-1 normally limits cortical forces in the embryo. UV laser-induced ablation of the cortex during mitosis showed that cyk-1 contributes to an increase in cortical rigidity. Thus, the effect of cyk-1 on spindle forces was likely due to changes in cortical elasticity. Additional experiments involving known components of the G-protein coupled cortical force generators also indicated that cyk-1 likely does not alter cortical forces by modulating this pathway directly. This work contributes additional insight into how microtubules and the actin cytoskeleton coordinately modulate spindle forces during asymmetric cell division.

• Subjects / Keywords

  • Force generators
  • Formin
  • CYK-1
  • Microtubules
  • C. elegans
  • Mitosis
  • Laulimalide
  • Microtubule binding agents

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3TQ5RW63

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.