Regulation of Chromosome Speeds in Mitosis

When chromosomes are being separated in preparation for cell division, their motions are slow (similar to 16 nm/s) relative to the speed at which many motor enzymes can move their cellular cargoes (160-1000 nm/s and sometimes even faster) and at which microtubules depolymerize (similar to 200 nm/s). Indeed, anaphase chromosome speeds are so slow that viscous drag puts little load on the mechanisms that generate the relevant forces (Nicklas, Adv. Cell Biol. 2:225, 1971). Available evidence suggests that chromosome speed is due to some form of regulation. For example, big and little chromosomes move at about the same speed, chromosomes that have farther to go move faster than others, and chromosome speed is affected by both temperature and an experimentally applied load. In this essay we review data on these phenomena and present our ideas about likely properties of the mechanisms that regulate chromosome speed.