Cytoskeleton

BIOGRAPHY

ACADEMIC POSITION:
Professor of Cell and Developmental Biology

RESEARCH INTERESTS:
Cells consist of many micro-environments, each dedicated to a distinct function. How do cells create these micro-environments, and how do they change in response to changes in a cell's surroundings? We use state-of-the-art real-time image analysis of live cells, genome-wide functional analyses, genetics, molecular genetics and biochemistry in mammalian cells and in budding yeast to elucidate the molecular mechanisms that underlie highly dynamic actin-mediated membrane trafficking events, which mediate formation of distinct cellular membrane compartments.

CURRENT PROJECTS:
• Membrane Trafficking and the Cytoskeleton. Using real-time microscopy and sophisticated analytical tools, coupled with genetics and molecular genetics, we have identified a pathway in budding yeast in which proteins are recruited to endocytic sites in a highly regular, sequential manner. Near the end of this process, a burst of actin assembly facilitates vesicle formation. By studying mutants of over 60 proteins, we have identified four protein modules that provide distinct functions in this pathway. Since actin is among the most highly conserved proteins known, we long believed that the results we obtain from studies in yeast would be directly transferable to more complex eukaryotes including humans. Defects in trafficking events and cytoskeletal proteins are linked to human diseases such as cancer and neural degeneration. We are isolating and characterizing mammalian homologues of cytoskeletal proteins that we first identified and characterized in yeast. We are particularly interested in determining the roles of these proteins in endocytosis and Golgi trafficking. Huntingtin interacting protein 1R (Hip1R) plays a critical role in productively harnessing forces of actin polymerization for steps in membrane trafficking.

• Actin Assembly. Elucidation of the molecular mechanisms used to regulate actin assembly will require a detailed knowledge of how actin subunits assemble into long polymers, and how proteins that bind to monomers and polymers affect assembly dynamics. We have performed a structure-function analysis of actin by mutating residues involved in nucleotide hydrolysis and assaying the effects of these mutations on actin assembly in vitro and in vivo. In complementary studies, genetic, biochemical and structural studies of the low molecular weight (16 kD) actin filament severing protein cofilin and its cofactor, Aip1p, and the actin nucleotide exchange factor, profilin, are being performed to determine how filament turnover is controlled in vivo. We have also identified and are studying several novel activators of the Arp2/3 complex, which regulates actin nucleation, and we are also studying the role of nucleotide in Arp2/3 function. By combining genetics with biochemistry, we are able to achieve a deeper understanding of actin regulation than would have been possible using either approach alone.