Spindle Orientation in Saccharomyces cerevisiae Depends on the Transport of Microtubule Ends along Polarized Actin Cables

• Published in: The Journal of cell biology 2003-05, Vol.161 (3), p.483-488
• Main Authors: Hwang, Eric, Kusch, Justine, Barral, Yves, Huffaker, Tim C.
• Format: Article
• Language: English
• Subjects: Actin Cytoskeleton - metabolism; Actin Cytoskeleton - ultrastructure; Actins; Cell Cycle Proteins - genetics; Cell Cycle Proteins - metabolism; Cell Polarity - physiology; Cells; Cells, Cultured; Cellular biology; Epithelial cells; Fluorescence; Green Fluorescent Proteins; Luminescent Proteins; Microfilaments; Microscopy; Microtubule Proteins - genetics; Microtubule Proteins - metabolism; Microtubules; Microtubules - metabolism; Microtubules - ultrastructure; Mitosis - physiology; Mitotic spindle apparatus; Models, Biological; Myosin Heavy Chains - genetics; Myosin Heavy Chains - metabolism; Myosin Type V - genetics; Myosin Type V - metabolism; Nuclear Proteins - genetics; Nuclear Proteins - metabolism; Protein Transport - physiology; Recombinant Fusion Proteins; Saccharomyces cerevisiae; Saccharomyces cerevisiae - cytology; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Spindle Apparatus - metabolism; Spindle Apparatus - ultrastructure; Yeasts
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.200302030

Microtubules and actin filaments interact and cooperate in many processes in eukaryotic cells, but the functional implications of such interactions are not well understood. In the yeast Saccharomyces cerevisiae, both cytoplasmic microtubules and actin filaments are needed for spindle orientation. In addition, this process requires the type V myosin protein Myo2, the microtubule end-binding protein Bim1, and Kar9. Here, we show that fusing Bim1 to the tail of the Myo2 is sufficient to orient spindles in the absence of Kar9, suggesting that the role of Kar9 is to link Myo2 to Bim1. In addition, we show that Myo2 localizes to the plus ends of cytoplasmic microtubules, and that the rate of movement of these cytoplasmic microtubules to the bud neck depends on the intrinsic velocity of Myo2 along actin filaments. These results support a model for spindle orientation in which a Myo2-Kar9-Bim1 complex transports microtubule ends along polarized actin cables. We also present data suggesting that a similar process plays a role in orienting cytoplasmic microtubules in mating yeast cells.