Our research aims to elucidate the molecular mechanisms that underlie cellular morphogenesis and plasma membrane dynamics in mammalian cells and in budding yeast. We are studying the functions and structure-function relationships of cytoskeletal proteins involved in morphogenesis and in membrane trafficking, and are elucidating the regulatory circuitry that controls the activity of these cytoskeletal proteins. The approaches employed for these studies include genome-wide functional analyses, genetics and molecular genetics, biochemistry, and real time image analysis of live cells.
Cell Polarity Development and Endocytosis in Budding Yeast. A large number of genes that control cellular morphogenesis and membrane trafficking in budding yeast have been identified. The challenge now is to determine how the products of these genes cooperate to control cell polarity development and trafficking events. The membrane actin cytoskeleton undergoes a carefully coordinated sequence of changes in organization during the cell cycle. These changes ultimately direct yeast morphological development and facilitate membrane trafficking events integral to morphogenesis. To understand how the organization of the cytoskeleton changes in response to a variety of signals, we have biochemically and genetically identified many yeast proteins that bind to actin filaments and regulate their assembly and/or organization. We have genetically tested the roles of these proteins in the living cell and have begun to study their spatial and temporal regulation by real-time fluorescence microscopy.
Membrane Trafficking Events in Mammalian Cells. Since actin is among the most highly conserved proteins known, we have long believed that the results we obtain from studies on the yeast actin cytoskeleton will 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. Recently, we have begun to isolate and characterize 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. One protein, huntingtin interacting protein 1R (Hip1R), which binds to the Huntingtin disease protein, plays a critical role in productively harnessing forces of actin polymerization for steps in membrane trafficking. We are also interested in investigating the roles of this and other cytoskeletal proteins in tumor cell invasion.
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.
In the News
Nine UC Berkeley faculty members have been elected to the American Academy of Arts and Sciences, bringing to 234 the total number of faculty now members of one of the nation's oldest and most prestigious honorary societies.