Tyrosines in the Kinesin-5 Head Domain Are Necessary for Phosphorylation by Wee1 and for Mitotic Spindle Integrity

Mitotic spindle assembly and maintenance relies on kinesin-5 motors that act as bipolar homotetramers to crosslink microtubules [1], [2], [3], [4] and [5]. Kinesin-5 motors have been the subject of extensive structure-function analysis [5], but the regulation of their activity in the context of mitotic progression remains less well understood [2]. We report here that Drosophila kinesin-5 (KLP61F) is regulated by Drosophila Wee1 (dWee1). Wee1 tyrosine kinases are known to regulate mitotic entry via inhibitory phosphorylation of Cdk1 [6], [7], [8], [9] and [10]. Recently, we showed that dWee1 also plays a role in mitotic spindle positioning through γ-tubulin and spindle fidelity through an unknown mechanism [11]. Here, we investigated whether a KLP61F-dWee1 interaction could explain the latter role of dWee1. We found that dWee1 phosphorylates KLP61F in vitro on three tyrosines within the head domain, the catalytic region that mediates movement along microtubules. In vivo, KLP61F with tyrosine→phenylalanine mutations fails to complement a klp61f mutant and dominantly induces spindle defects similar to ones seen in dwee1 mutants. We propose that phosphorylation of the KLP61F catalytic domain by dWee1 is important for the motor's function. This study identifies a second substrate for a Wee1 kinase and provides evidence for phosphoregulation of a kinesin in the head domain.     

THE TAXONOMIC SIGNIFICANCE OF ANTHOCHLORS IN THE SUBTRIBE COREOPSIDINAE (COMPOSITAE,HELIANTHEAE)

Anthochlors (chalcones and aurones) are found in a number of plant families including the Compositae. Within this family they were once thought to occur only in the subtribe Coreopsidinae of the tribe Heliantheae. More recent studies show them to occur also in the tribes Cardueae, Eupatorieae, Helineae, Inuleae, and Lactuceae. This has suggested that anthochlors are no longer good taxonomic markers for the Coreopsidinae. A survey of 69 of approximately 210 genera of the Heliantheae shows anthochlors present only in the Coreopsidinae except for Helianthus, Simsia, Tithonia, and Viguiera, closely related genera of the subtribe Helianthinae. Of the 32 genera of the Coreopsidinae recently recognized, 30 were surveyed from available material and all contain anthochlors except Guardiola and Venegasia. The results indicate that, despite some variation, anthochlors are still good taxonomic markers for the Coreopsidinae. This represents the only case within the family in which a particular type of flavonoid is taxonomically diagnostic at the subtribal level.