Arrested cells are Mad as Hec

The spindle checkpoint works even when on the move, according to new results from Silvia Martin-Lluesma, Volker Stucke, and Erich Nigg (Max-Planck Institute of Biochemistry, Martinsried, Germany). Against all that has been sacred in the field, these researchers find that mitosis can be arrested when checkpoint proteins leave the kinetochore.

The checkpoint is activated by Mad1 and Mad2 proteins, which bind to kinetochores that are not attached to the spindle microtubules. The prevailing theory has been that release of Mad1/Mad2 inactivates the checkpoint and allows mitosis to proceed.

Nigg and colleagues looked for human Mad1-interacting proteins and found Hec1, which recruited Mad1 and Mad2 to kinetochores. Given this function, the group was surprised to find that reducing Hec1 prevented cells from dividing, despite the fact that Mad1/Mad2 were not on the...