Centrosome and kinetochore movement during mitosis.

During the past year important progress has been made in refining our understanding of how chromosomes become equally distributed to daughter cells during mitosis. Unlike the situation in diatoms and yeast, it now appears that spindle pole (centrosome) separation during spindle formation and anaphase B is mediated in vertebrates primarily by an astral pulling, and not a pushing, mechanism. Kinetochore motility is directionally unstable, which has important consequences for how chromosomes move to the equator of the forming spindle. Finally, the observation that sister chromatid disjunction occurs even in the presence of high levels of maturation promoting factor reveals that the series of biochemical events responsible for this phenomenon is not an obligatory part of the pathway by which the cell exits mitosis.