Temperature dependence of anaphase chromosome velocity and microtubule depolymerization

The time course of chromosome movement and decay of half-spindle birefringence retardation in anaphase have been precisely determined in the endosperm cell of a plant Tilia americana and in the egg of an animal Asterias forbesi. For each species, the anaphase retardation decay rate constant and chromosome velocity are similar exponential functions of temperature. Over the temperature range at which these cells can complete anaphase, chromosome velocity and retardation rate constant yield a positive linear relationship when plotted against each other. At the higher temperatures where the chromosomes move faster, the spindle retardation decays faster, even though the absolute spindle retardation is greater. Chromosome velocity thus parallels the anaphase spindle retardation decay rate, or rate of spindle microtubule depolymerization, rather than absolute spindle retardation, or the amount of microtubules in the spindle. These observations suggest that a common mechanism exists for mitosis in plant and animal cells. The rate of anaphase chromosome movement is associated with an apparent first-order process of spindle fiber disassembly. This process irreversibly prevents spindle fiber subunits from participating in the polymerization equilibrium and removes microtubular subunits from chromosomal spindle fibers.