Biomedical Sciences Graduate Program(s)
Biochemistry, Molecular Biology and Genetics
Microbiology, Immunology and Infectious Diseases
Molecular Cell and Developmental Biology
Research Description
My lab studies a mitotic regulatory system that is essential in maintaining
genomic stability and preventing tumor progression in certain types of
cancers. We are studying the "spindle checkpoint" in the budding yeast
Saccharomyces cerevisiae using a combination of genetics, cell biology,
molecular biology, biochemistry and molecular genetics. The spindle
checkpoint prevents cells from entering anaphase if even a single chromosome
is detached from the spindle. Many of the yeast genes that constitute the
spindle checkpoint have been identified. There are mammalian homologs of
each, and recent evidence suggests that mutations in some of these genes are
responsible for genomic instability that accompanies tumor progression in a
variety of cancer cells. Therefore, this mitotic checkpoint is
evolutionarily conserved and is vital for maintaining genomic stability in
organisms from yeast to humans. We have used classical yeast genetics to
determine that cell cycle arrest via the checkpoint is induced when
kinetochore function is impaired. This suggests that yeast cells monitor
kinetochore attachment to the spindle and arrest cell division when
attachments are incomplete. Recently we have cloned mammalian homologs of
three of the yeast genes and shown that the checkpoint proteins are
localized to the kinetochore. This suggests a provocative model where
localizing checkpoint proteins to the kinetochore may be required to sense
that chromosomes are detached from the spindle and may be an important
aspect of generating the inhibitory mitotic signal. We are interested in
determining the role that the kinetochore plays in spindle checkpoint
function. We have mapped the sites of interaction within the kinetochore and
determined that checkpoint function is dependent on a subset of kinetochore
proteins. We are also investigating the molecular basis for
kinetochore-microtubule interactions. We have identified kinetochore mutants
that are defective in attaching chromosomes to the mitotic spindle. We are
using a genetic approach to identify and characterize the genes responsible
to elucidate the molecular mechanisms responsible for this critical event in
the cell cycle. We are also continuing our genetic analysis of the spindle
checkpoint by looking for new genes required for checkpoint function. We are
using a dominant mutant that activates the spindle checkpoint as a starting
point to identify recessive mutants that eliminate checkpoint function. We
are also using the dominant mutant to identify new genes required to turn
off the checkpoint when cells enter anaphase. The long-term goal is to have
a complete molecular description of the checkpoint in both yeast and human
cells. Some anti-cancer chemotherapies employ compounds like taxol, that
inhibit cell division by activating the spindle checkpoint. We have
developed a strain for high throughput screening of chemical compounds that
inhibit key regulatory components of the cell cycle. We are using strains
that have temperature sensitive mutations in cell cycle genes and looking
for synthetic interactions that compromise the growth of the cells. We are
beginning with cdc20 mutants, because Cdc20 is the target of the spindle
checkpoint. Our goal is to find compounds, like taxol that are potent
anti-cancer agents. We have obtained the complete set of deletion mutants of
every ORF in the yeast genome and have completed a genome-wide screen for
sensitivity to anti-tubulin drugs. This kind of approach should provide
novel targets for combination treatments to sensitize cancer cells to
chemotherapeutic agents. Finally, we are developing new approaches to
genome-wide screens to identify new genes that interact with the spindle
checkpoint and the response to this important class of anti-cancer drugs.
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