Kinesin-13 regulates the quantity and quality of tubulin inside cilia.
Bottom Line: Loss of both Kin13Bp and Kin13Cp resulted in slow cell multiplication and motility, overgrowth of cell body microtubules, shortening of cilia, and synthetic lethality with either paclitaxel or a deletion of MEC-17/ATAT1, the α-tubulin acetyltransferase.The mutant cilia beat slowly and axonemes showed reduced velocity of microtubule sliding.Thus kinesin-13 positively regulates the axoneme length, influences the properties of ciliary tubulin, and likely indirectly, through its effects on the axonemal microtubules, affects the ciliary dynein-dependent motility.
Affiliation: Department of Cellular Biology, University of Georgia, Athens, GA 30602;Show MeSH
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Mentions: Deletions of either KIN13B or KIN13C did not affect the rate of cell multiplication (Figure 2A) or the gross phenotype, except for a mild decrease in the motility rate in the absence of KIN13C (Figure 2B). Kin13Bp and Kin13Cp have a similar domain organization (Figure 1A), and the sequences of their motor domains indicate that they originated from a recent gene duplication (Wickstead et al., 2010). We hypothesized that Kin13Bp and Kin13Cp have partially redundant functions. About half of the homozygotes lacking both Kin13Bp and Kin13Cp (13BC-KO) were viable (Table 1) but grew and swam more slowly than the single knockouts (Figure 2, A–D, Supplemental Figure S3, A–D, and Supplemental Movie S1). A phosphodiesterase inhibitor, IBMX, increases the swim speed of Tetrahymena by increasing the ciliary beat frequency (Hennessey and Lampert, 2012). IBMX (1 mM) increased the swimming rate of the 13BC-KO mutants, but they remained slower than the similarly treated wild-type cells (Figure 2E and Supplemental Movies S2 and S3). The slow cell motility indicates an abnormal function of the locomotory cilia. The 13BC-KO cells also had a reduced rate of phagocytosis, a function that depends on the motility of oral cilia (Supplemental Figure S3E). Shaking of the 13BC-KO flask cultures caused further reduction in the multiplication and motility rates, whereas this treatment had little effect on the wild-type cells (Figure 2, A and B). The phenotypes of some ciliary mutants are enhanced by increased aeration (Brown et al., 2003; Hou et al., 2007), again indicating that Kin13Bp and Kin13Cp affect cilia. Whereas Kin13Cp localized strongly to the CVP, a microtubule-rich organelle involved in osmoregulation (Allen and Naitoh, 2002), we did not detect a change in the sensitivity of 13BC-KO cells to either hypoosmotic or hyperosmotic conditions (unpublished data).
Affiliation: Department of Cellular Biology, University of Georgia, Athens, GA 30602;