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. Author manuscript; available in PMC: 2013 May 1.
Published in final edited form as: Trends Cell Biol. 2012 Apr 3;22(5):241–249. doi: 10.1016/j.tcb.2012.02.007

Figure 3. Chromatin-dependent pathways of microtubule assembly.

Figure 3

During M-Phase, spindle assembly factors (SAFs) are sequestered by Importins that bind to their NLS. A gradient of active Ran (RanGTP; orange) centered on chromosomes locally releases spindle assembly factors (SAFs) from the inhibitory effect of Importins. In parallel, Aurora B, which is activated by clustering at the inner centromere or on microtubules, phosphorylates and inhibits the microtubule depolymerase MCAK, and Oncoprotein 18 (OP18) to reduce its ability to sequester tubulin heterodimers. The Ran and CPC-dependent pathways create a locally favorable environment for microtubule and spindle assembly.