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 My lab studies two regulatory systems essential in maintaining genome stability and preventing tumor progression in certain types of cancers.  We primarily study the “spindle checkpoint” in the budding yeast Saccharomyces cerevisiae using a combination of genetic and molecular genetic approaches. The spindle checkpoint is a regulatory mechanism that inhibits the onset of anaphase until all chromosomes achieve bipolar orientation on the spindle.  We have a poor understanding about how the spindle signal is generated and two general models that can be considered. The first is that the lack of tension is the initiating event and this model has almost completely dominated the field. The best data has come from studies of grasshoppers and mantid spermatocytes because they have large chromosomes that can be micromanipulated. The data clearly show that the lack of tension on detached chromosomes activates the spindle checkpoint however the mechanism may be restricted to meiotic cells. The second possibility is that the checkpoint monitors microtubule occupancy and if a kinetochore is unoccupied, then the cells arrest in mitosis. 

     Both models can accommodate a role for the kinetochore in generating the spindle checkpoint signal.  We have provided definitive evidence for a role of the kinetochore in checkpoint signaling in yeast. Several kinetochore mutants lack the spindle checkpointWe have mapped the checkpoint activity of the kinetochore to the Ndc80 complex of proteins that has a dual role in chromosome segregation and checkpoint signaling. We are currently identifying mutations in the Ndc80 complex that specifically disrupt the spindle checkpoint. 

     We have recently identified an important phosphorylation event on Mad3 that is required to transmit the signal for the tension branch of the spindle checkpoint. We have raised a phospho-specific antibody to a phosphorylated Mad3 peptide and showed that phosphorylation requires all spindle checkpoint genes and the Ndc80 complex.  We are using the antibody to further map the tension checkpoint within the kinetochore.

     We have recently discovered that there is cross talk between the spindle checkpoint and the DNA damage checkpoint.  We have used genetic analysis to show that DNA damage activates the canonical spindle checkpoint pathway except that DNA damage regulates the pathway in a kinetochore-independent fashion.  This suggests that the kinetochore is not obligatory for spindle checkpoint proteins to become inhibitors.