Kinesin-13 regulates flagellar, interphase, and mitotic microtubule dynamics in Giardia intestinalis

Department of Molecular and Cell Biology, University of California-Berkeley, 341 LSA Bldg., Berkeley, CA 94720-3200; Section of Microbiology, 255 Briggs Hall, UC Davis, Davis, CA 95616

^* To whom correspondence should be addressed. Email: scdawson{at}ucdavis.edu.

	Abstract

Microtubule depolymerization dynamics in the spindle are regulated by kinesin-13, a non-processive kinesin motor protein that depolymerises microtubules at plus and minus ends. Here we show that a single kinesin-13 homolog (a non-processive depolymerising motor) regulates flagellar length dynamics as well as other interphase and mitotic dynamics in Giardia intestinalis, a widespread parasitic diplomonad protist. Both GFP-tagged kinesin-13 and EB1 (a plus end-tracking protein) localize to the plus ends of mitotic and interphase microtubules including a novel localization to the eight flagellar tips, cytoplasmic anterior axonemes and the median body. The ectopic expression of a kinesin-13 (S280N) rigor mutant construct caused significant elongation of the eight flagella with significant decreases in the median body volume, and resulted in mitotic defects. Notably, drugs that disrupt normal interphase and mitotic microtubule dynamics also affected flagellar length in Giardia. This work extends recent work on interphase and mitotic kinesin-13 functioning in metazoans, to include a role in regulating flagellar length dynamics. We suggest that kinesin-13 universally regulates both mitotic and interphase microtubule dynamics in diverse microbial eukaryotes and propose that axonemal microtubules are subject to the same regulation of microtubule dynamics as other dynamic microtubule arrays. Finally, this study represents the first use of a dominant negative strategy to disrupt normal protein function in Giardia, and provides important insights into giardial microtubule dynamics with relevance to the development of anti-giardial compounds that target critical functions of kinesins in the giardial life cycle.