Spindle fusion requires dynein-mediated sliding of oppositely oriented microtubules

Curr Biol. 2009 Feb 24;19(4):287-96. doi: 10.1016/j.cub.2009.01.055.

Abstract

Background: Bipolar spindle assembly is critical for achieving accurate segregation of chromosomes. In the absence of centrosomes, meiotic spindles achieve bipolarity by a combination of chromosome-initiated microtubule nucleation and stabilization and motor-driven organization of microtubules. Once assembled, the spindle structure is maintained on a relatively long time scale despite the high turnover of the microtubules that comprise it. To study the underlying mechanisms responsible for spindle assembly and steady-state maintenance, we used microneedle manipulation of preassembled spindles in Xenopus egg extracts.

Results: When two meiotic spindles were brought close enough together, they interacted, creating an interconnected microtubule structure with supernumerary poles. Without exception, the perturbed system eventually re-established bipolarity, forming a single spindle of normal shape and size. Bipolar spindle fusion was blocked when cytoplasmic dynein function was perturbed, suggesting a critical role for the motor in this process. The fusion of Eg5-inhibited monopoles also required dynein function but only occurred if the initial interpolar separation was less than twice the microtubule radius of a typical monopole.

Conclusions: Our experiments uniquely illustrate the architectural plasticity of the spindle and reveal a robust ability of the system to attain a bipolar morphology. We hypothesize that a major mechanism driving spindle fusion is dynein-mediated sliding of oppositely oriented microtubules, a novel function for the motor, and posit that this same mechanism might also be involved in normal spindle assembly and homeostasis.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Cell Polarity
  • Chromosome Segregation
  • Dyneins / metabolism*
  • Kinesin / genetics
  • Kinesin / metabolism
  • Microtubule-Associated Proteins / metabolism
  • Microtubules / metabolism*
  • Oocytes / cytology
  • Oocytes / physiology
  • Spindle Apparatus / metabolism*
  • Xenopus Proteins / genetics
  • Xenopus Proteins / metabolism
  • Xenopus laevis

Substances

  • KIF11 protein, Xenopus
  • Microtubule-Associated Proteins
  • Xenopus Proteins
  • Dyneins
  • Kinesin