Destructive testing on mitotic machinery: Probing the mechanics of fission yeast cell division by laser ablation.

Abstract

When eukaryotic cells divide, the mitotic spindle has the critical task of segregating chromosomes, ensuring that each new daughter cell receives exactly one copy of its genetic information. To do so, it must self-assemble and then generate force to pull chromosomes to the right place at the right time. While decades of work has produced a detailed census of many of the molecules required for cell division, considerable gaps remain in our understanding of the mechanics of mitosis. How is force exerted in the correct locations at the correct times? How does force propagate between structures with different material properties, and how are those properties themselves tuned for different functions? How can complex cellular machinery self-assemble without a “director” telling all the parts where to go? Due to its structurally simple mitotic spindle, which consists of a single bundle of around a dozen microtubules, the fission yeast S. pombe is a particularly apt system for probing biophysical mechanism. Importantly, S. pombe undergoes closed cell division, which means its spindle assembles within the nuclear envelope. Considerable changes in envelope shape accompany spindle elongation and chromosome segregation, but the mechanical interactions between the nuclear envelope and the mitotic spindle are poorly understood. I will present work combining live cell confocal imaging, laser ablation, quantitative analysis, and molecular perturbations to examine how the fission yeast cytoskeleton accomplishes the mechanical functions required for cell division, and how it coordinates with the nuclear envelope. I will also discuss how laser ablation reveals mechanical differences between the S. pombe spindle and that of its sister species, S. japonicus, which undergoes semi-open mitosis. These differences suggest how features of spindle organization may evolve to match their mechanical constraints.