title: She1-mediated inhibition of dynein motility along astral microtubules promotes polarized spindle movements.
abstract: BACKGROUND
  Cytoplasmic dynein motility along microtubules is critical for diverse cellular processes ranging from vesicular transport to nuclear envelope breakdown to mitotic spindle alignment. In yeast, we have proposed a regulated-offloading model to explain how dynein motility drives microtubule sliding along the cortex, powering transport of the nucleus into the mother-bud neck [1, 2]: the dynein regulator She1 limits dynein offloading by gating the recruitment of dynactin to the astral microtubule plus end, a prerequisite for offloading to the cortex. However, whether She1 subsequently affects cortically anchored dynein activity during microtubule sliding is unclear.
  
  
  RESULTS
  Using single-molecule motility assays, we show that She1 strongly inhibits dynein movement along microtubules, acting directly on the motor domain in a manner independent of dynactin. She1 has no effect on the motility of either Kip2, a kinesin that utilizes the same microtubule track as dynein, or human kinesin-1, demonstrating the specificity of She1 for the dynein motor. At single-molecule resolution, She1 binds tightly to and exhibits diffusional behavior along microtubules. Diffusive She1 collides with and pauses motile dynein motors, prolonging their attachment to the microtubule. Furthermore, Aurora B/Ipl1 directly phosphorylates She1, and this modification appears to enhance the diffusive behavior of She1 along microtubules and its potency against dynein. In cells, She1 dampens productive microtubule-cortex interactions specifically in the mother compartment, polarizing spindle movements toward the bud cell.
  
  
  CONCLUSIONS
  Our data reveal how inhibitory microtubule-associated proteins selectively regulate motor activity to achieve unidirectional nuclear transport and demonstrate a direct link between cell-cycle machinery and dynein pathway activity.
authors.affiliation: Biology Department, University of Massachusetts Amherst, 221 Morrill South, 611 North Pleasant Street, Amherst, MA 01003, USA.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Markus
authors.forename: Katelyn A
authors.initials: KA
authors.lastname: Kalutkiewicz
authors.forename: Wei-Lih
authors.initials: WL
authors.lastname: Lee
mesh_terms: D004398:Dyneins / Q000378:metabolism*; D016547:Kinesins / Q000378:metabolism*; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism*; D020409:Molecular Motor Proteins / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism*; D024701:Myosin Type V / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D008941:Spindle Apparatus / Q000502:physiology*
chemical_list: C075341:KIP2 protein, S cerevisiae; D008869:Microtubule-Associated Proteins; D020409:Molecular Motor Proteins; C098732:Myo4 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D024701:Myosin Type V; D018995:Myosin Heavy Chains; D004398:Dyneins; D016547:Kinesins