Ran-GTP regulates kinetochore attachment in somatic cells.

The Ran GTPase controls multiple mitotic processes in Xenopus egg extracts, including mitotic checkpoints, spindle assembly and post-mitotic nuclear envelope reassembly. We have analyzed Ran's role in somatic cells. We uncovered a novel mitotic role of Ran-GTP, involving the Crm1 nuclear export receptor. This pathway is an important mode of Ran-GTP function during mitosis in mammalian somatic cells, which mediates the recruitment of the RanGAP1/RanBP2 complex to kinetochores and maintains the microtubule-based fibers connecting kinetochores to spindle poles (k-fibers). Here we discuss potential implications of these findings for normal k-fiber assembly.