The awesome power of multiple model systems: interpreting the complex nature of spindle checkpoint signaling.

The spindle checkpoint coordinates the cell biology of mitosis with cell-cycle progression. It ensures that sister-chromatid separation only takes place when all kinetochores have formed stable bipolar microtubule attachments. Here, we discuss recent advances in our understanding of what activates this checkpoint pathway, the molecular nature of the checkpoint signal and its mode of transmission, and how the checkpoint might be inactivated.