Spindle assembly checkpoint satisfaction occurs via end-on but not lateral attachments under tension

J Cell Biol. 2017 Jun 5;216(6):1533-1542. doi: 10.1083/jcb.201611104. Epub 2017 May 23.


To ensure accurate chromosome segregation, the spindle assembly checkpoint (SAC) prevents anaphase until all kinetochores attach to the spindle. What signals the SAC monitors remains unclear. We do not know the contributions of different microtubule attachment features or tension from biorientation to SAC satisfaction nor how these possible cues change during attachment. In this study, we quantify concurrent Mad1 intensity and report on SAC silencing, real-time attachment geometry, occupancy, and tension at individual mammalian kinetochores. We show that Mad1 loss from the kinetochore is switch-like with robust kinetics and that tension across sister kinetochores is established just before Mad1 loss events at the first sister. We demonstrate that CenpE-mediated lateral attachment of the second sister can persistently generate this metaphase-like tension before biorientation, likely stabilizing sister end-on attachment, yet cannot induce Mad1 loss from that kinetochore. Instead, Mad1 loss begins after several end-on microtubules attach. Thus, end-on attachment provides geometry-specific molecular cues or force on specific kinetochore linkages that other attachment geometries cannot provide.

Publication types

  • Video-Audio Media
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism
  • Chromosomal Proteins, Non-Histone / genetics
  • Chromosomal Proteins, Non-Histone / metabolism
  • Chromosome Segregation*
  • Humans
  • Kinetics
  • Kinetochores / metabolism
  • Kinetochores / physiology*
  • M Phase Cell Cycle Checkpoints*
  • Mechanotransduction, Cellular*
  • Microscopy, Video
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism
  • Spindle Apparatus / metabolism
  • Spindle Apparatus / physiology*
  • Stress, Mechanical
  • Time-Lapse Imaging


  • Cell Cycle Proteins
  • Chromosomal Proteins, Non-Histone
  • Nuclear Proteins