Experiments focus on the dynamics of microtubule assembly in spindles during the process of meiosis using live imaging of labeled microtubules. We utilize cranefly spermatocytes isolated into acute cultures containing cells at various stages of cell division that can be studied for several hours. Microtubule dynamics are studied by the technique of fluorescent speckle imaging whereby spermatocytes are injected with low concentrations of fluorescent-labeled tubulin that incorporates into microtubules at low density. This creates a patterned, discontinuous labeling of microtubules that enables quantification of the rates and sites of assembly. We currently are testing the role of tension as a modulator of microtubule polymerization during anaphase. Chromosome kinetochores exert dragging forces on attached microtubule ends favoring microtubule assembly as chromosomes move from spindle equator to spindle poles. However, microtubule disassembly is induced when dragging forces are eliminated by laser ablation of attached chromosomes. These observations may reveal some of the self-organizing mechanisms that control the orderly separation of chromosomes during cell division.