title: Condensin and the spindle midzone prevent cytokinesis failure induced by chromatin bridges in C. elegans embryos.
abstract: BACKGROUND
  During cell division, chromosomes must clear the path of the cleavage furrow before the onset of cytokinesis. The abscission checkpoint in mammalian cells stabilizes the cleavage furrow in the presence of a chromatin obstruction. This provides time to resolve the obstruction before the cleavage furrow regresses or breaks the chromosomes, preventing aneuploidy or DNA damage. Two unanswered questions in the proposed mechanistic pathway of the abscission checkpoint concern factors involved in (1) resolving the obstructions and (2) coordinating obstruction resolution with the delay in cytokinesis.
  
  
  RESULTS
  We found that the one-cell and two-cell C. elegans embryos suppress furrow regression following depletion of essential chromosome-segregation factors: topoisomerase II(TOP-2), CENP-A(HCP-3), cohesin, and to a lesser degree, condensin. Chromatin obstructions activated Aurora B(AIR-2) at the spindle midzone, which is needed for the abscission checkpoint in other systems. Condensin I, but not condensin II, localizes to the spindle midzone in anaphase and to the midbody during normal cytokinesis. Interestingly, condensin I is enriched on chromatin bridges and near the midzone/midbody in an AIR-2-dependent manner. Disruption of AIR-2, the spindle midzone, or condensin leads to cytokinesis failure in a chromatin-obstruction-dependent manner. Examination of the condensin-deficient embryos uncovered defects in both the resolution of the chromatin obstructions and the maintenance of the stable cleavage furrow.
  
  
  CONCLUSIONS
  We postulate that condensin I is recruited by Aurora B(AIR-2) to aid in the resolution of chromatin obstructions and also helps generate a signal to maintain the delay in cytokinesis.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Joshua N
authors.initials: JN
authors.lastname: Bembenek
authors.forename: Koen J C
authors.initials: KJ
authors.lastname: Verbrugghe
authors.forename: Jayshree
authors.initials: J
authors.lastname: Khanikar
authors.forename: Györgyi
authors.initials: G
authors.lastname: Csankovszki
authors.forename: Raymond C
authors.initials: RC
authors.lastname: Chan
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D064107:Aurora Kinase B / Q000235:genetics* / Q000378:metabolism; D017173:Caenorhabditis elegans / Q000166:cytology* / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000235:genetics* / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D002970:Cleavage Stage, Ovum / Q000378:metabolism; D048749:Cytokinesis; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D008856:Microscopy, Fluorescence; D046912:Multiprotein Complexes / Q000235:genetics* / Q000378:metabolism; D008941:Spindle Apparatus / Q000378:metabolism; D013997:Time Factors
chemical_list: D029742:Caenorhabditis elegans Proteins; D002843:Chromatin; D004268:DNA-Binding Proteins; D046912:Multiprotein Complexes; C108312:condensin complexes; D064107:Aurora Kinase B; C491506:air-2 protein, C elegans; D000251:Adenosine Triphosphatases