Biology

Prof. Richard McIntosh, Distinguished Professor Emeritus, University of Colorado, USA
Zoom link https://zoom.us/j/91000724968?pwd=Zk55dFpXa09jNGcvS2UramRNRkxyZz09 Meeting ID 910 0072 4968 Passcode 485544

Abstract:

Microtubules (MTs) must form at the onset of cell division to build the mitotic spindle that will segregate the already duplicated chromosomes. During mitosis, MTs are dynamically unstable: forming, shortening, and fluxing toward the spindle poles. As the spindle functions, some MTs depolymerize while others elongate, and at the end of mitosis, all spindle MTs disappear. This talk will explore the roles of MT dynamics in the mechanical actions of spindles on chromosomes. Early evidence demonstrated that MT shortening accompanies chromosome-to-pole motion, but whether this depolymerization is causal, regulatory, or permissive for chromosome motion has remained an active debate. To explore this issue, I will describe the structural pathways for tubulin addition and loss from MTs and review evidence that MT growth and shortening can generate force. I will then look at the evidence for MT dynamics at various stages of mitosis in several species to ask whether there are universal behaviors amid the biological variability. I will also discuss the more limited information about the dispensability of minus end-directed motors for anaphase chromosome segregation. In conclusion, I will present my opinions on what this evidence suggests about the mechanisms for mitotic chromosome motion.