The kinesin-14 Klp2 is negatively regulated by the SIN for proper spindle elongation and telophase nuclear positioning
In S. pombe, a late mitotic kinase pathway called the Septation Initiation Network (SIN) triggers cytokinesis. Here, we show that the SIN is also involved in regulating anaphase spindle elongation and telophase nuclear positioning via inhibition of Klp2, a minus end directed kinesin-14. Klp2 is known to localize to microtubules (MTs) and have roles in interphase nuclear positioning, mitotic chromosome alignment, and nuclei migration during karyogamy (nuclear fusion during mating). We observe SIN-dependent disappearance of Klp2 from MTs in anaphase and we have found that this is mediated by direct phosphorylation of Klp2 by the SIN kinase Sid2 which abrogates loading of Klp2 onto MTs by inhibiting its interaction with Mal3 (EB1 homolog). Disruption of Klp2 MT localization is required for efficient anaphase spindle elongation. Furthermore, when cytokinesis is delayed, SIN inhibition of Klp2 acts in concert with microtubules emanating from the equatorial microtubule organizing center to position the nuclei away from the cell division site. These results reveal novel functions of the SIN in regulating the MT cytoskeleton and suggest that the SIN may have broader functions in regulating cellular organization in late mitosis than previously realized.