The Stukenberg lab studies kinetochores using egg extracts, cells and embryos of the frog Xenopus laevis. We utilize two in vivo systems, Xenopus tissue culture cells and Xenopus embryos, to test predictions from our in vitro results. Current work has focused on the Aurora B kinase which is a critical mitotic regulator that localizes to the inner centromere region from prophase to anaphase. We recently discovered that Aurora B regulates microtubule dynamics, chromosome congression and the spindle checkpoint. We are dissecting how Aurora B itself is regulated and identifying the important substrates that are regulated by Aurora B for proper mitotic progression. The lab is also studying a relatively new component of the outer kinetochore that is highly conserved from yeast to humans referred to as the Ndc80 complex. The Ndc80 complex is required for proper kinetochore assembly, microtubule binding and chromosome congression. In collaboration with our neighbors, the Burke lab, we have shown that the complex is a critical mediator of the spindle checkpoint. An exciting question for the future is how the Ndc80 complex and Aurora B can coordinate microtubule binding and spindle checkpoint signaling