-
|
-
|
-
|
-
|
-
|
-
|
-
|
Chromosome Segregation, the Mitotic Checkpoint, and Aneuploidy.
Accurate delivery of one copy of each chromosome is essential every time a cell duplicates, a process that takes place millions of times every day in every individual. Errors in this process cause misdistribution of chromosomes (aneuploidy), which early in development lead to lethal developmental defects and later are hallmarks of human tumor progression. The goal of the laboratory is to elucidate the principles of chromosome segregation and to identify and understand the roles of individual proteins involved. Our primary approach is to reconstruct the cell cycle in the test tube using a cell-free system derived from the African frog Xenopus laevis eggs. In addition, we are using mammalian cultured cells to identify and characterize the key factors important for chromosome segregation in mitosis.
Kinetochore microtubule attachment. The accurate segregation of chromosomes in mitosis requires the stable attachment of microtubules to kinetochores, the protein complex assembled at each centromere - a discrete locus on each chromosome. The details of this complex and dynamic process are poorly understood. We are evaluating the roles of kinetochore associated proteins and microtubule effectors, including motors, kinases, and microtubule associated proteins, in stable kinetochore microtubule attachment in Xenopus egg extracts and mammalian cultured cells, and developing in vitro reconstitution using purified components.
The mitotic checkpoint. Eukaryotic organisms have evolved a "mitotic checkpoint" to prevent premature advance to anaphase prior to successful attachment of every chromosomes to microtubules of the mitotic spindle. Various mitotic checkpoint proteins are recruited onto unattached kinetochores, where they generate a diffusible signal to prevent chromosome segregation. Current efforts, using a convergence of cell biology and biochemistry to determine the functional properties of kinetochore components (including BubR1, Bub3, Mad1, Mad2, and Cdc20), are underway to dissect this major cell cycle control mechanism that maintains genome integrity.
Anti-mitotic drugs. Cancer is above all else a disease of cell proliferation. Directly targeting the mitotic apparatus has been an effective approach that has been used for many years. However, most anti-mitotic drugs target microtubule - the major component of the mitotic spindle. Because these drugs, such as taxanes and vinca alkaloids, do not distinguish between microtubules involved in mitosis and those involved in cell motility, cell shape, and intracellular transport in neurons, they frequently associate with significant toxic side effects, including neuropathy, myelosuppression, and cardiomyopathy. It has recently been appreciated that other components of the mitotic spindle, that are only expressed in mitotically-active cells, can also be targeted to produce mitotic defects that lead to apoptotic cell death. In collaboration with the laboratory of Dr. Steven Rosenfeld, we are screening for inhibitors of mitotic motors, such as the mitotic kinesin Eg5.
