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Microtubule motor protein Kar3 is required for normal mitotic division and morphogenesis in Candida albicans
Racquel Kim Sherwood1, Richard J Bennett
1Department of Molecular Microbiology and Immunology, Brown University, 171 Meeting St., Providence, RI 02912, USA.
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.
Insights
The kinesin Kar3 protein is essential for nuclear division and cell morphology in Candida albicans. Loss of Kar3 disrupts mitosis, causing cell cycle delays and altered growth patterns.
Area of Science:
- Microbiology
- Cell Biology
- Molecular Motors
Background:
- The kinesin-related protein Kar3 (Kar3p) is a minus end-directed molecular motor involved in microtubule-based nuclear movements.
- Previous studies indicated Kar3p's critical role in nuclear fusion (karyogamy) during Candida albicans mating.
Purpose of the Study:
- To investigate the role of Kar3p in nuclear migration and cell morphology during Candida albicans mating and mitosis.
- To elucidate the impact of Kar3p loss on cell cycle progression, nuclear division, and spindle stability.
Main Methods:
- Phenotypic analysis of kar3 mutants in mating and vegetative growth conditions.
- Microscopy to assess nuclear congression, migration, and spindle morphology.
- Cell cycle analysis to identify delays and abnormalities.
Main Results:
- Kar3p is required for nuclear congression during mating but not for initial migration in the mating projection.
- Loss of Kar3p impairs cell and colony morphology, reducing filamentation and increasing pseudohypha formation during mitosis.
- Kar3p deficiency leads to slow growth, reduced viability, delayed cell cycle progression with anaphase accumulation, and unstable mitotic spindles.
- Kar3 protein localizes to spindle pole bodies, suggesting a role in mitotic division.
Conclusions:
- Kar3p plays crucial roles in both nuclear congression during mating and mitotic cell division in Candida albicans.
- Defects in Kar3p function result in aberrant nuclear division, spindle instability, and altered cell morphology, likely due to anaphase delays.
- The study highlights Kar3p's multifaceted functions beyond nuclear migration, impacting overall cell fitness and morphology.
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