The Expanded Kinesin-13 Repertoire of Trypanosomes Contains Only One Mitotic Kinesin Indicating Multiple Extra-Nuclear Roles

Bill Wickstead,Eva Gluenz,Keith Gull,Jamie T Carrington,Eric J Bernhard

doi:10.1371/journal.pone.0015020

Abstract

BackgroundKinesin-13 proteins have a critical role in animal cell mitosis, during which they regulate spindle microtubule dynamics through their depolymerisation activity. Much of what is known about Kinesin-13 function emanates from a relatively small sub-family of proteins containing MCAK and Kif2A/B. However, recent work on kinesins from the much more widely distributed, ancestral Kinesin-13 family, which includes human Kif24, have identified a second function in flagellum length regulation that may exist either alongside or instead of the mitotic role.Methodology/Principal FindingsThe African trypanosome Trypanosoma brucei encodes 7 distinct Kinesin-13 proteins, allowing scope for extensive specialisation of roles. Here, we show that of all the trypanosomal Kinesin-13 proteins, only one is nuclear. This protein, TbKIN13-1, is present in the nucleoplasm throughout the cell cycle, but associates with the spindle during mitosis, which in trypanosomes is closed. TbKIN13-1 is necessary for the segregation of both large and mini-chromosomes in this organism and reduction in TbKIN13-1 levels mediated by RNA interference causes deflects in spindle disassembly with spindle-like structures persisting in non-mitotic cells. A second Kinesin-13 is localised to the flagellum tip, but the majority of the Kinesin-13 family members are in neither of these cellular locations.Conclusions/SignificanceThese data show that the expanded Kinesin-13 repertoire of trypanosomes is not associated with diversification of spindle-associated roles. TbKIN13-1 is required for correct spindle function, but the extra-nuclear localisation of the remaining paralogues suggests that the biological roles of the Kinesin-13 family is wider than previously thought.

Highlights

The kinesin superfamily comprises a set of molecular motors that couple ATP hydrolysis to force production
These data show that six trypanosomal Kinesin-13 sequences belong to the largest and most widely distributed Kinesin-13 subfamily, Kinesin-13A. This subfamily may be the ancestral Kinesin-13 type [2;20], and contains the human kinesin Kif24, as well as the only Kinesin-13 proteins encoded by the single-celled organisms Chlamydomonas [19] and Giardia [18] (Fig. 1). We have named these proteins TbKIN13-1, -2, -3, -4a, -4b and -5 to follow on from the nomenclature of LmjKIN13-1 and LmjKIN13-2 used for 2 proteins studied in the related parasite Leishmania major [20;23]
We have investigated the expanded Kinesin-13 family found in the protozoan parasite Trypanosoma brucei

Summary

Introduction

The kinesin superfamily comprises a set of molecular motors that couple ATP hydrolysis to force production. This force is used by cells in the movement of various cargo along microtubules, and in the regulation of microtubule dynamics. Within the superfamily as a whole, a number of distinct kinesin families can be determined on the basis of primary sequence of the protein motor domain These families represent conserved groups of sequences which often have similar cellular functions (see [1;2]). Kinesin-13 proteins have a critical role in animal cell mitosis, during which they regulate spindle microtubule dynamics through their depolymerisation activity. Recent work on kinesins from the much more widely distributed, ancestral Kinesin-13 family, which includes human Kif, have identified a second function in flagellum length regulation that may exist either alongside or instead of the mitotic role

Methods

Results

Conclusion