The Role of Ran in Regulating Microtubule Spindle Assembly

Abstract

To ensure the equal segregation of chromosomes when a cell divides, the cell erects a bipolar scaffold, the mitotic spindle, onto which chromosomes attach and along which the sister chromatids separate. The positioning and timing of spindle formation must be carefully regulated for the chromosomes to be equally segregated into the two daughter cells. Recent studies have found that the GTPase Ran may have a central role in regulating bipolar spindle assembly. Ran·GTP can stimulate spindle assembly in vitro in the absence of both chromosomes and centrosomes. Ran regulates spindle assembly in the same way it facilitates nucleocytoplasmic transport; namely Ran regulates the interaction of specific proteins with nuclear transport receptors. Subsequently, Ran was found to affect several processes involved in spindle assembly including microtubule dynamics, spindle pole assembly, and microtubule motor protein activity. This chapter will focus on the role of Ran in microtubule spindle assembly and the implications these data have on potential roles for Ran in mitosis.