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Colloquium

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March 7, 2014

March 13 Colloquium

Kwonmoo Lee, Harvard Medical School

Integrating Protein Dynamics and Cell Mechanics: Mechanosensitivity of Dynamic Actin Remodeling During Cell Migration

Migrating cells are mechanochemical machines where biochemistry and mechanics integrate to control cellular motion. The polymerization of the filamentous protein called actin provides force generation for membrane protrusion, an initial step of cell migration. In turn, mechanical force sensed by cells leads to dynamic responses of the intracellular biochemical pathways. The dissection of systems with such mechanochemical pathways has remained a fundamental challenge in biological investigation.

To unravel the complex nature of interplay between biochemistry and mechanics in space and time, we developed a novel statistical approach based on local image sampling and registration to directly visualize the dynamics of molecular/cellular events at the subcellular level. This method revealed distinct dynamics of molecular factors and traction force involved in cell protrusion, allowing us to establish in situ their differential functions. This quantitative framework also allowed us to exploit natural heterogeneity of cell protrusion to extract statistical relationships between different molecular/cellular events. Using this method we suggest that linear actin filaments along with adhesion formation initiate new protrusions. Then, the linear filaments undergo a structural transition to branched networks, mediated by exponential actin polymerization. Furthermore, we showed that increasing membrane tension during protrusion promotes this structural tension which leads to stronger force generation to support edge advancement against the membrane tension. This suggests that migrating cells can reorganize their biochemical machinery in response to mechanical cues in a highly dynamic manner at a time scale of 10 seconds. It also highlights that mechanical processes are tightly integrated with biochemical pathways and modulate protein dynamics, thereby playing critical roles in cell physiology.

REFRESHMENTS:  3:40 p.m. in the Willamette Atrium COLLOQUIUM:   4:00 p.m. in Willamette 100

March 5, 2014

March 6 Colloquium

Wolfgang Altmannshofer, Perimeter Institute

The Flavor Puzzle

The known basic building blocks of matter, the quarks and leptons, come in three generations or flavors.
The masses and interactions of the different flavors show a very hierarchical structure and the origin of these hierarchies remains an unsolved mystery of particle physics.The same hierarchies lead to a very high sensitivity of flavor changing processes to new undiscovered particles even outside the reach of direct searches at particle colliders.In this colloquium I will discuss the status of our understanding of flavor and highlight the complementarity of flavor and collider physics in searching for new phenomena at the TeV scale and beyond.

 

REFRESHMENTS:  3:40 p.m. in the Willamette Atrium COLLOQUIUM:   4:00 p.m. in Willamette 100

February 28, 2014

March 4 Colloquium

Timothy Cohen, SLAC

What Light Can Teach Us About Dark Matter

Consistency between big bang cosmology and precision data requires that about 80% of the matter in our Universe consists of a new particle — the dark matter.  Uncovering the identity of this state is one of the driving motivations for exploring theories beyond the Standard Model of particle physics.  One compelling hypothesis is that the dark matter is a massive particle whose only interactions occur via gravity and the weak force.  This so-called WIMP paradigm leads to a wide variety of experimental signatures.  In this colloquium, I will argue that one compelling way to explore WIMP models is by analyzing measurements of cosmic ray photons.  I will provide a pair of case studies to demonstrate the kind of physics that can be extracted from gamma-ray data.  The first is an analysis of the Fermi line at 130 GeV, with an emphasis on the implications for WIMP models; the second demonstrates that data from H.E.S.S. can be used to constrain compelling models for multi-TeV WIMPs.  These examples will illuminate how much there is to learn about the nature of dark matter by studying light.

REFRESHMENTS:  3:40 p.m. in the Willamette Atrium COLLOQUIUM:   4:00 p.m. in Willamette 100

February 26, 2014

February 27 Colloquium

Hernan Garcia, Princeton University

How, When and Where in Pattern Formation: Spying on Embryonic Development One Molecule at a Time

An abiding mystery in the study of living matter is how a single cell develops into a multicellular organism. As this cell divides, its progeny read the program encoded on their DNA and adopt different fates becoming familiar cell types such as those found in muscle, liver and our brains. We now know that the decisions that cells make during development are not so much based on which genes to express, but rather on when, where and how to express them. Despite advances in determining the identities of the molecules that mediate these decisions we are still incapable of predicting how simple physical parameters such as the number, position and affinity of binding sites for these molecules on the DNA determine developmental fates. Using the fruit fly, one of the classic model systems for embryonic development, I will show how a combination of new technologies, quantitative experiments, and statistical mechanics is providing new insights about cellular decision making during development. In particular, I will describe how the specification of macroscopic body parts in an organism is linked to the non-equilibrium molecular-scale processes inside single cells. The goal of this interdisciplinary research is to produce a predictive understanding of developmental programs which will enable the rational control of biological size, shape and function.

  •  REFRESHMENTS:  3:40 p.m. in the Willamette Atrium
  • COLLOQUIUM:   4:00 p.m. in Willamette 100
February 22, 2014

February 25 Colloquium

Nathaniel Craig, Rutgers University

The Once and Future Higgs

The discovery of a Higgs boson at the LHC marks both the culmination of a decades-long quest for the final piece of the Standard Model and the dawn of a new era in the search for more fundamental physics. I’ll explore the ways in which the Higgs provides a powerful tool in the hunt for physics beyond the Standard Model through its production, propagation, and decays.

  •  REFRESHMENTS:  3:40 p.m. in the Willamette Atrium
  • COLLOQUIUM:   4:00 p.m. in Willamette 100
February 17, 2014

February 20 Colloquium

Takemichi Okui, Florida State University

Searching For Matter-Antimatter Asymmetry Through the Higgs Boson

Abstract: Despite its extraordinary success as a theory of the microscopic world, the standard model of particle physics fails to explain some crucial cosmological observations. An example of such is the fact that we only see matter but no antimatter in the universe, while the standard model is too symmetric between matter and antimatter. I will discuss how to probe a possible new source of matter-antimatter asymmetry in the properties of the newly-discovered Higgs boson in future LHC data.

  •  REFRESHMENTS:  3:40 p.m. in the Willamette Atrium
  • COLLOQUIUM:   4:00 p.m. in Willamette 100

 

February 10, 2014

February 13, 2014 Colloquium

G.D. Bothun, University of Oregon

Global Climate Change IS Increasing Weather Volatility

 For many people, climate change is perceived to manifest as a systematic shift away from average weather to some kind of new average weather.  A priori, there was never any physical reason to expect this kind of behavior; only glacial-interglacial dynamics produces these shifts.  As a consequence, denial of climate change is rising because there is no perception of an average weather change.    However, climate is a complex and non-linear interplay between the surface ocean heat distribution and the atmospheric heat distribution and the natural timescales in those systems is different by three orders of magnitude.   By adding energy (now measureable) to the atmospheric-ocean interface, humans have changed pathways and exchange rates, leading to a non-linear response of the system that is manifest as climate volatility.   This climate volatility easily now appears in the data.  Three most recent examples are a) two extreme polar vortex intrusions to very southerly latitudes, b) last summer’s incredibly weak jet stream that lead to prolonged retrograde storms (storms that move from east to west) and c) the conditions that spawned SuperStorm Sandy.    This talk will make the case that climate volatility is quite real, that some non-linear thresholds are being reached, that increases in deep tropical convection may be the principle driver of the currently observed volatility, and that the connections between the oceans and the atmosphere are deeper and more complicated that previously appreciated.    Most all of this has come to light within just the last 3-4 years due to significant advances in observational instrumentation and computational modeling and has re-written climate literacy 101.

  • REFRESHMENTS:  3:40 p.m. in the Willamette Atrium
  • COLLOQUIUM:   4:00 p.m. in Willamette 100
February 5, 2014

Thursday, February 6 Colloquium

Stefania Gori, Perimeter Institute of Theoretical Science

Beyond the Higgs boson discovery

Abstract: After almost five decades from its first theoretical proposal, the most wanted elementary particle, the Higgs boson, or something that closely looks like it, has finally been discovered by the Large Hadron Collider (LHC) at CERN. I will review the crucial role of this discovery for the self-consistency of the “Standard Model” of particle physics. I will discuss what we expect to learn from dedicated measurements of Higgs properties about fundamental physics that cannot be explained in the framework of the Standard Model.

  • REFRESHMENTS:  3:40 p.m. in the Willamette Atrium
  • COLLOQUIUM:   4:00 p.m. in Willamette 100
  • HOST:  Graham Kribs
February 3, 2014

February 4 Colloquium

Tristan Ursell, Stanford University

Growth and Shape Control in Bacteria

Abstract: In bacteria, a host of enzymes regulates the reproducible and robust construction of the cell wall, whose mechanical integrity is crucial for viability under osmotic stress. Antibiotics that target these enzymes disrupt cell wall construction, ultimately leading to mechanical failure of the cell. Our work explores the physical mechanisms of cell growth and death, as a guide to understanding antibiotic mechanisms that disrupt mechanical properties of the cell. We use a combination of cell wall fluorescent labeling, high resolution time-lapse microscopy, and computational image processing to characterize where, and with what dynamics, cell wall and outer membrane growth occurs. Analysis of cell-surface marker fluorescence indicates that the cytoskeleton is present at sites of active growth and that chemical depolymerization of the cytoskeleton causes homogeneous, unstructured growth and eventual cell death by rupture. When combined with cell-shape analysis, our data strongly suggest that dynamic localization of the bacterial cytoskeleton is part of a curvature sensing and growth feedback mechanism that orchestrates heterogeneous growth to maintain cell shape and regulate mechanical stress. Using surface-specific protein labeling, we show that outer membrane growth also occurs in a similar heterogeneous manner. Quantitative tracking of growth is an effective method for characterizing cell wall mechanical failure resulting from antibiotic treatment. These techniques pave the way for studying the detailed dynamics of growth-associated proteins and their disturbance by antibiotics.

Host: Raghuveer Parthasarathy

January 28, 2014

January 30 Colloquium

Kun Zhao, University of California, Los Angeles

From Colloids to Bacteria:Anisotropy in Self-Organizing Systems at the Mesoscopic Scale

Abstract:  Many complex mesoscopic systems, ranging from inorganic colloids to active biological cells, exhibit a rich variety of pattern-forming behavior. In this talk, I will show you how anisotropy in two model systems, anisotropic shaped colloids and bacterial communities, affect complex pattern formation. During the directed self-assembly of colloidal systems, shape anisotropy can greatly influence resulting structures. We have developed a technique called roughness controlled depletion attraction which allows us to probe the phase space of 2D Brownian systems for a variety of anisotropic shapes such as triangles, squares, and other polygons. We have discovered several unanticipated effects, such as local symmetry breaking in a triatic liquid crystal phase of uniform triangles. Anisotropy also plays a large role in the formation of bacterial communities called biofilms. Biofilms are a major human health hazard as well as being an impediment in many industrial and medical settings. By using condensed matter techniques, we present for the first time the dynamics of colony formation at early stages of biofilm development for Pseudomonas aeruginosa. We found that Pseudomonas aeruginosa does not follow an isotropic random walk as commonly assumed, but instead obeys a new form of polysaccharide-guided dynamics such that the distribution of surface.

Host: Raghuveer Parthasarathy

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