A Novel Microtubule-Depolymerizing Kinesin Involved in Length Control of a Eukaryotic Flagellum

Abstract

Cilia and flagella are complex, microtubule (MT)-filled cell organelles of which the structure is evolutionarily conserved from protistan cells to mammalian sperm and the size is regulated. The best-established model for flagellar length (FL) control is set by the balance of continuous MT assembly and disassembly occurring at the flagellar tip. Because steady-state assembly of tubulin onto the distal end of the flagellum requires intraflagellar transport (IFT)--a bidirectional movement of large protein complexes that occurs within the flagellum--FL control must rely upon the regulation of IFT. This does not preclude that other pathways might "directly" affect MT assembly and disassembly. Now, among the superfamily of kinesins, family-13 (MCAK/KIF2) members exhibit a MT-depolymerizing activity responsible for their essential functions in mitosis. Here we present a novel family-13 kinesin from the flagellated protozoan parasite Leishmania major, that localizes essentially to the flagellum, and whose overexpression produces flagellar shortening and knockdown yields long flagella. Using negative mutants, we demonstrate that this phenotype is linked with the MT-binding and -depolymerizing activity of this kinesin. This is the first report of an effector protein involved in FL control through a direct action in MT dynamics, thus this finding complements the assembly-disassembly model.

EB1 and EB3 promote cilia biogenesis by several centrosome-related mechanisms

“…EB3 interacts with the MT depolymerizing kinesin-13 MCAK (Lee et al, 2008). Kinesin-13 family proteins have been implicated in cilium disassembly in protists (Blaineau et al, 2007;Dawson et al, 2007;Piao et al, 2009), and EB3 might, therefore, stabilize the axoneme by counteracting such proteins.…”

Inhibition of active nuclear transport is an intrinsic trigger of programmed cell death in trypanosomatids

“…Transfection and RNAi induction were as described. 41 Briefly, 10 mg of linearised plasmid DNAs were transfected into 3.10 7 cells of the 29-13 cell line. An exponential protocol was used with 1500 V and 25 mF as parameters.…”

Centrosomal protein CEP104/ChlamydomonasFAP256 moves to the ciliary tip during cilia assembly

“…Among these are the MT plus-end-binding proteins EB1 and EB3 and the nonprocessive kinesin motor kinesin-13. The latter has been shown to be involved in MT depolymerization at the plus and minus ends of MTs (Hunter et al, 2003;Wordeman, 2005) and homologs of Kinesin-13 have been linked to axonemal assembly and disassembly through overexpression and knockout studies in a variety of protistans (Blaineau et al, 2007;Chan and Ersfeld, 2010;Dawson et al, 2007). Another member of the kinesin superfamily, Kif19A, which depolymerizes MTs from the plus ends, also localizes at the tips of motile cilia.…”