Microtubule Motor Protein Kar3 Is Required for Normal Mitotic Division and Morphogenesis in Candida albicans

Abstract

The kinesin-related protein Kar3 is a minus end-directed molecular motor that plays a multifunctional role in microtubule-directed nuclear movement. Previously, it was shown that Candida albicans Kar3p is critical for nuclear fusion during mating as kar3 mutants were defective in karyogamy. In this study, we confirm that Kar3p is required for nuclear congression in mating but that neither Kar3p nor the dynein motor protein Dyn1p is required for nuclear migration in the mating projection prior to cell fusion. In addition, we show that C. albicans Kar3p plays an important role in the cell and colony morphology of mitotically dividing cells, as evidenced by diminished filamentation of kar3 cells on Spider medium and an increased tendency of mutant cells to form pseudohyphal cells in liquid culture. Loss of Kar3p also led to defects in nuclear division, causing cells to grow slowly and exhibit reduced viability compared to wild-type cells. Slow growth was due, at least in part, to delayed cell cycle progression, as cells lacking Kar3p accumulated in anaphase of the cell cycle. Consistent with a role in mitotic division, Kar3 protein was shown to localize to the spindle pole bodies. Finally, kar3 cells exhibited unstable or aberrant mitotic spindles, a finding that accounts for the delay in cell cycle progression and decreased viability of these cells. We suggest that the altered morphology of kar3 cells is a direct consequence of the delay in anaphase, and this leads to increased polarized growth and pseudohypha formation.

Stress-Induced Phenotypic Switching inCandida albicans

“…This led to the hypothesis that increased rates of white-opaque switching were a direct consequence of longer generation times. We subsequently examined several other slow growing strains in the laboratory, including a strain lacking the molecular motor KAR3, as well as a strain expressing fluorescently labeled histone (H2B) and tubulin (Tub2) proteins (Sherwood and Bennett, 2008). Both of these strains exhibit a significant delay in cell generation times, growing at least 10% slower than SC5314 (see Sherwood and Bennett, 2008; Table 3).…”

“…We subsequently examined several other slow growing strains in the laboratory, including a strain lacking the molecular motor KAR3, as well as a strain expressing fluorescently labeled histone (H2B) and tubulin (Tub2) proteins (Sherwood and Bennett, 2008). Both of these strains exhibit a significant delay in cell generation times, growing at least 10% slower than SC5314 (see Sherwood and Bennett, 2008; Table 3). In addition, we found that white colonies from ⌬/⌬kar3 and H2B/Tub2-labeled strains also switched to opaque at high frequency (25 and 22%, respectively; Table 4), thereby supporting a connection between cell growth and switching.…”

“…For determination of the doubling time of cells grown on SCD medium containing hydrogen peroxide, single cells were visualized using time-lapse microscopy and growth rates were measured as described previously (Sherwood and Bennett, 2008).…”

Candida albicans Kinesin Kar3 Depends on a Cik1-Like Regulatory Partner Protein for Its Roles in Mating, Cell Morphogenesis, and Bipolar Spindle Formation

“…albicans Kar3 (CaKar3) is a kinesin-14 family member that has been shown to function in mitotic division and is critical for hypha formation and nuclear fusion during mating (9,11). Its homolog in Saccharomyces cerevisiae has similar functions in mitosis and mating that are enabled by interactions with two kinesinlike proteins: S. cerevisiae Cik1 (ScCik1) and ScVik1 (12)(13)(14)(15)(16)(17)(18)(19)(20).…”

“…Hyphae are the invasive form and are important for virulence during systemic infections as well as for biofilm formation (1,5,6). In all of these morphological states, microtubuleassociated motor proteins play major roles in microtubule cytoskeleton remodeling, nuclear movements, chromosome segregation, and cargo transport (7)(8)(9). This provides a rationale for their use as novel targets for antifungal drugs (10).…”