14-3-3 regulation of Ncd reveals a new mechanism for targeting 4 proteins to the spindle in oocytes

The meiotic spindle is formed without centrosomes in a large volume of oocytes. Local activation of crucial spindle proteins around chromosomes is important for formation and maintenance of a bipolar spindle in oocytes. We found that the phospho-docking 14-3-3 proteins stabilise spindle bipolarity in Drosophila oocytes. A critical 14-3-3 target is the minus-end directed motor Ncd (human HSET; kinesin-14) which has well documented roles in stabilising a bipolar spindle in oocytes. Phospho-docking by 14-3-3 inhibits the microtubule binding activity of the non-motor Ncd tail. Further phosphorylation by Aurora B kinase can release Ncd from this inhibitory effect of 14-3-3. As Aurora B localises to chromosomes and spindles, 14-3-3 facilitates specific association of Ncd with spindle microtubules by preventing Ncd from binding to non-spindle microtubules in oocytes. Therefore, 14-3-3 translates a spatial cue provided by Aurora B to target Ncd selectively to the spindle within the large volume of oocytes.