Professor of Cell Biology
365 Biotechnology Building
Tim Huffaker is a Professor of Cell Biology. He received a B.A. degree in Chemistry from the University of California at Santa Cruz and a Ph.D. degree in Biology from the Massachusetts Institute of Technology. He was a Helen Hay Whitney Foundation postdoctoral fellow at MIT where he began his studies on microtubule function in yeast. He joined the faculty at Cornell in 1988 and is a member of both the Graduate Field of Biochemistry, Molecular and Cell Biology and the Graduate Field of Genetics and Development. His research is funded by the National Institutes of Health.
During every cell generation, chromosomes are replicated and sister chromosomes are segregated to each of the daughter cells. The segregation of chromosomes involves a complex cellular machine called the mitotic spindle. The major components of the mitotic spindle are molecular fibers that connect chromosomes to the spindle poles and the poles to each other. These fibers are called microtubules and are composed of two proteins, alpha and beta-tubulin. In addition, a large number of other proteins are involved in spindle function. Although many of these proteins are as yet uncharacterized, they are thought to include microtubule motor proteins that mediate movements of chromosomes, regulatory proteins that influence microtubule assembly, and structural proteins that are required for spindle assembly and function. These proteins work together to form an extremely efficient machine; in yeast, a chromosome is missegregated only once in every 100,000 cell divisions.
The aim of our lab is to identify proteins involved in mitotic spindle function in the yeast Saccharomyces cerevisiae and to study the function of these proteins at the molecular level. With its sophisticated molecular genetics, increasingly powerful cell biology tools, and relatively simple mitotic spindle, yeast is a particularly tractable organism for these studies.
Our research is focused on several microtubule-binding proteins that are necessary for proper chromosome segregation. These proteins, which were identified in a variety of genetic screens, bind to microtubules in vitro and colocalize with microtubules in vivo. We have made mutations in the genes encoding these proteins and are examining the effects of these mutations in vivo. Our phenotypic analysis of mutants relies on fluorescence microscopy which we use to look for defects in chromosome segregation, spindle orientation, spindle elongation, and microtubule dynamics. By using a variety of GFP constructs, we are able to examine these processes in real time in living cells. For example, recent work has shown that loss of the microtubule-binding protein Stu2p dampens microtubule dynamics, interferes with spindle orientation, and blocks spindle elongation and chromosome segregation. This work demonstrates that Stu2p plays a role in the regulation of microtubule dynamics and that this regulation is essential for spindle function.
In a collaboration with Tony Bretscher's lab, we are examining the connection between microtubules and actin filaments in yeast. Both cytoplasmic microtubules and actin cables are known to play roles in orienting the spindle in yeast. We have shown that this process requires a type V myosin of yeast, Myo2p, and established a molecular linkage between actin cables and cytoplasmic microtubules. Our results suggest that Myo2p, in a complex with one or more microtubule-binding proteins, moves along actin cables and pulls the cytoplasmic microtubules in the bud.
Legend to Figure
Visualization of cytoplasmic microtubules in living cells using alpha-tubulin-GFP. Images are of a single cell taken at 10 second intervals. Two microtubules are observed growing and shrinking.
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Click here to view Dr. Huffaker's PubMed listings.