Probing force balance in the S. pombe mitotic spindle by laser ablation

A microtubule-based machine called the mitotic spindle segregates chromosomes when eukaryotic cells divide. In the fission yeast S. pombe, which undergoes closed mitosis, the spindle forms a single bundle of microtubules inside the nucleus. During elongation, the spindle extends via antiparallel microtubule sliding by molecular motors. These extensile forces from the spindle resist compressive forces from inside the nucleus. We probe the source of this force balance via laser ablation of spindles at various stages of mitosis. We find that spindle pole bodies collapse toward each other following ablation, but that spindle geometry is often rescued, allowing spindles to resume elongation. While this basic behavior has been previously observed [1,2], many questions remain as to the timing, mechanics, and molecular requirements of these phenomena. Here, we quantify the time scales of both the relaxation and rescue responses and probe their molecular requirements. We test the possible mechanical roles of nuclear envelope-, centrosome- and microtubule-based forces.
[1] A. Khodjakov, et al. Curr. Biol., 2004.[2] I. Tolic-Nørrelykke et al, Curr. Biol. 2004.