Figure 1.

The Ran gradient regulates different stages of mitosis. (a) Following nuclear envelope breakdown, active Ran (Ran-GTP) levels remain as a gradient that decreases from chromatin towards the cortex (orange gradient – dark orange is low) [13,16]. RCC1, the RanGEF that generates active Ran, remains associated with chromatin, while RanGAP generates inactive Ran (Ran-GDP) and is cytosolic [12]. There is an inverse gradient of importins bound to NLS-containing proteins, which is highest near the cortex (blue gradient – dark blue is high) [4]. (b) Cartoon schematics show a cell in metaphase (left) and anaphase (right) with the relative locations of active Ran (orange gradient) and importin-bound proteins (blue gradient) [13,16]. The legend indicates the components of the cell with chromatin (red), centrosome (black), central spindle microtubules (green), astral microtubules (purple), kinetochore microtubules (grey) and contractile proteins (pink). During metaphase, the spindle is controlled by the high levels of Ran-GTP around chromatin, while in anaphase, importin-binding facilitates the cortical localization of proteins such as anillin to control polarity [1,12]