Constitutive Mad1 targeting to kinetochores uncouples checkpoint signalling from chromosome biorientation

Nat Cell Biol. 2011 Apr;13(4):475-82. doi: 10.1038/ncb2223. Epub 2011 Mar 13.


Accurate chromosome segregation depends on biorientation, whereby sister chromatids attach to microtubules from opposite spindle poles. The spindle-assembly checkpoint is a surveillance mechanism in eukaryotes that inhibits anaphase until all chromosomes have bioriented. In present models, the recruitment of the spindle-assembly checkpoint protein Mad2, through Mad1, to non-bioriented kinetochores is needed to stop cell-cycle progression. However, it is unknown whether Mad1-Mad2 targeting to kinetochores is sufficient to block anaphase. Furthermore, it is unclear whether regulators of biorientation (for example, Aurora kinases) have checkpoint functions downstream of Mad1-Mad2 recruitment or whether they act upstream to quench the primary error signal. Here, we engineered a Mad1 construct that localizes to bioriented kinetochores. We show that the kinetochore localization of Mad1 is sufficient for a metaphase arrest that depends on Mad1-Mad2 binding. By uncoupling the checkpoint from its primary error signal, we show that Aurora, Mps1 and BubR1 kinases, but not Polo-like kinase, are needed to maintain checkpoint arrest when Mad1 is present on kinetochores. Together, our data suggest a model in which the biorientation errors, which recruit Mad1-Mad2 to kinetochores, may be signalled not only through Mad2 template dynamics, but also through the activity of widely conserved kinases, to ensure the fidelity of cell division.

Publication types

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

MeSH terms

  • Calcium-Binding Proteins / genetics
  • Calcium-Binding Proteins / metabolism
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • Chromosome Segregation*
  • HeLa Cells
  • Humans
  • Kinetochores / metabolism*
  • Mad2 Proteins
  • Microtubules / metabolism
  • Mitosis / physiology*
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism
  • Signal Transduction / physiology*
  • Spindle Apparatus / metabolism*


  • Calcium-Binding Proteins
  • Cell Cycle Proteins
  • MAD1L1 protein, human
  • MAD2L1 protein, human
  • Mad2 Proteins
  • Nuclear Proteins
  • Recombinant Fusion Proteins
  • Repressor Proteins