Unless otherwise noted, lectures are held the second Tuesday of each month at 4:00 PM in 341 Bardeen.

September 8th - Aneuploidy Both Promotes and Suppresses Tumors

Beth Weaver
Department of Pharmacology
University of Wisconsin-Madison

Aneuploidy, an abnormal chromosome number, is a hallmark of tumor cells. Recognizing this correlation, Boveri proposed aneuploidy to be a cause of tumorigenesis nearly 100 years ago. However, despite its nearly ubiquitous occurrence in malignant cells, a cause-and-effect relationship between aneuploidy and cancer has been difficult to define. This is because most methods of generating aneuploidy produce additional cellular defects that can also promote tumorigenesis, such as DNA damage. We determined that cells and mice with reduced levels of the mitosis-specific, centromere-linked motor CENP-E develop aneuploidy and chromosomal instability without other defects, including DNA damage. CENP-E+/- cells missegregate one or a few chromosomes per division. As Boveri had proposed, the low rate of whole chromosome missegregation caused by CENP-E heterozygosity in the absence of other defects drives an elevated level of spontaneous spleen and lung tumors. However, aneuploidy due to CENP-E heterozygosity suppresses tumors in three different contexts: spontaneous tumors of the liver, tumors caused by treatment with the carcinogen DMBA, and tumors caused by homozygous loss of the p19/ARF tumor suppressor. All three contexts in which CENP-E heterozygosity suppresses tumors have a pre-existing level of aneuploidy that can be increased by depletion of CENP-E. Reduction of CENP-E also causes increased cell death in these contexts. Together, these results support the hypothesis that high rates of chromosome missegregation promote cell death and tumor suppression. We further tested this hypothesis by co-depleting CENP-E and another component of the mitotic checkpoint, Mad2. CENP-E+/-; Mad2+/- double heterozygous cells missegregate more chromosomes per division than CENP-E+/- or Mad2+/- single heterozygous cells and have elevated levels of cell death. CENP-E+/-; Mad2+/- double heterozygous mice exhibit decreased rates of tumor development as compared to mice with reduced levels of CENP-E or Mad2 individually. These findings indicate that while low rates of chromosome missegregation can promote tumorigenesis, higher rates of chromosome missegregation drive cell death and tumor suppression.

October 13th - Neurogranin's Role in Synaptic Plasticity

Nashaat Gerges
Department of Cell Biology, Neurobiology and Anatomy
Medical College of Wisconsin

Synaptic plasticity, which is thought to be the cellular correlate of learning and memory, is the ability of synapses to change their strength and remodel. The two most commonly studied forms of synaptic plasticity are long term potentiation (LTP) and long term depression (LTD). In CA1 hippocampal synapses, both forms of synaptic plasticity are dependent on NMDA receptor activation and coexist in a tight balance that is dependent on calmodulin availability. Neurogranin is one of the most abundant postsynaptic proteins that act as a calmodulin buffer. Neurogranin is a neuron-specific protein that is enriched in hippocampus and cortex. Neurogranin levels are decreased in many neurological disorders (Alzheimer’s disease, Schizophrenia, hypothyroidism and aging). Interestingly, neurogranin levels are also correlated with memory performance. While there is evidence that neurogranin plays an essential role in synaptic plasticity and neurological diseases, its exact molecular mechanism is not well-understood. Using a combination of electrophysiology, biochemistry, confocal and electron microscopy, this talk will discuss the role of neurogranin in synaptic plasticity.

March 9th - In Vivo Imaging of Synaptic Plasticity and Pathology
Note Location Change: Room 5235 MSC

Wen-Biao Gan
Skirball Institute for Biomolecular Medicine
and Department of Physiology and Neuroscience
New York University School of Medicine

The mammalian brain possesses not only remarkable plasticity for learning but also extraordinary stability for long-term memory storage. Although much is known about cellular and molecular mechanisms underlying learning, the structural basis for maintaining long-term memory remains unidentified. By developing a transcranial two-photon imaging technique to study changes in postsynaptic dendritic spines in living mouse cerebral cortex, we have shown that the majority of dendritic spines in diverse regions of the cortex can last throughout adult life. Recently, we have found that a small fraction of new spines induced by novel experience, together with most spines formed early during development and surviving experience-dependent elimination, are preserved and provide a structural basis for memory retention throughout the entire life of an animal. These studies indicate that learning and daily sensory experience leave minute but permanent marks on cortical connections and suggest that lifelong memories are stored in largely stably connected synaptic networks.

To extend our research into medicine field, we have investigated synaptic pathology in mouse model of Alzheimer’s disease (AD) and experimental autoimmune encephalomyelitis (EAE). We have found that fibrillar amyloid deposition is associated with large-scale disruption of synaptic connectivity in a mouse model of AD. In addition, we show that CNS inflammation causes early and extensive remodeling of synaptic connections in the EAE mouse brain. Together, these studies suggest that disruption of stable synaptic connections contributes significantly to the pathogenesis of neurological disorders, underscoring the importance of maintaining synaptic stability in the treatment of brain diseases.

April 13th - Imaging Circuit Assembly in the Vertebrate Retina
Note Location Change: Room 5235 MSC

Rachel Wong
Department of Biological Structure
University of Washington

The assembly of neural circuits requires the generation of specific cell types, their positioning within the circuit and establishing appropriate patterns of connectivity between synaptic partners. Using the vertebrate retina as our model system, we utilize in vivo and in vitro imaging approaches to investigate the cellular mechanisms underlying the formation and maintenance of appropriate synaptic connectivity patterns between subsets of retinal neurons. Our studies have revealed previously unexpected strategies by which retinal neurons form their circuitry.

April 30th - Signalling and Mechanics at the Mitotic Centromere and Kinetochore
Special Lecture

Jason Swedlow
College of Life Sciences
University of Dundee, Scotland

Kinetochore Dynamics. A hallmark of mitosis in most eukaryotic cells is the formation of a metaphase plate half-way between the spindle poles, about which chromosomes exhibit oscillatory movements and centromere ‘breathing’. The relationships between oscillations, breathing, and formation of the metaphase plate, and the molecular components that regulate these processes, are poorly understood. We have developed a 4D live cell imaging assay that includes a fully automatic computational image analysis pipeline to determine how the different components of centromeres and kinetochores contribute to the dynamics of the metaphase plate. Our assay shows that the baseline oscillation and breathing speeds in late prometaphase and metaphase are set by microtubule depolymerases, while oscillation and breathing periods depend on the stiffness of the mechanical linkage between sisters. It also reveals that metaphase plates become thinner as cells progress towards anaphase, due to a progressive reduction in oscillation speed at relatively constant oscillation period. Based on these results, we propose that metaphase plate formation requires tight control of the state of the mechanical linkage between sisters, i.e. the centromeric chromatin and cohesion, to regulate the activation and deactivation of microtubule depolymerases in sister kinetochores.

Image Informatics. The Open Microscopy Environment (OME) is a multi-site collaborative effort among academic laboratories and a number of commercial entities that produces open tools to support data visualization, management, and analysis for biological light microscopy and high content screening (HCS). Designed to interact with existing commercial software, all OME formats and software are free, and all OME source code is available under GNU public "copyleft" licenses. With a strong foundation for biological light microscopy in place, OME has begun extending its coverage to other fields of biological imaging. We have successfully developed a data model for HCS data, and are currently releasing preview versions of software for HCS data management and analysis, with full releases scheduled for June 2010.

OME develops and releases three different components:
1. The OME Data Model (http://ome-xml.org) provides a specification for saving metadata and exchanging metadata in microscopy and HCAs.
2. The OME-TIFF file format (http://ome-xml.org/wiki/OmeTiff) and the Bio-Formats file format library (http://openmicroscopy.org/site/products/bio-formats) provide an easy-to-use set of tools for converting data from proprietary file formats.
3. The OMERO platform (http://openmicroscopy.org/site/products/omero) is a Java-based server and client application suite that combines an image metadata database, a binary image data repository and high performance visualization and analysis. OMERO includes interfaces for Java, C/C++ and Python to support a wide variety of client applications and support for Matlab-based applications like CellProfiler. For computational analysis of microscopy or HCS images, this standardised interface provides a single mechanism for accessing image data of all types-- regardless of the original file format. OMERO is used in the Columbus data management system from PerkinElmer, Inc., the softWoRx DMS system from Applied Precision, Inc. and is the engine that runs the JCB DataViewer (http://jcb-dataviewer.rupress.org), the first publication system for original image data in the life sciences. More information is available at http://openmicroscopy.org.

May 11th - Bioprobe-Assisted Analysis on Protein-Protein Interactions within an Intact Drosophila Neuron

Akira Chiba
Department of Biology
University of Miami

Life as carried out by individual proteins happens in vivo. Yet, most of what we know of protein-protein interactions is derived from studies using yeast, cell culture, or ex vivo. I introduce an approach that uses a vital molecular bioprobe to link interacting proteins to specific in situ contexts. Using i-Probe (protein interactor bioprobe) designed for Cdc42 GTPase, I show that Cdc42’s signaling partners are pre-localized as ~1 µm3 spots at the base of dendrites 4 hours prior to dendrite initiation in the aCC motoneuron of Drosophila. Such subcellular resolutions further allow demonstration that Pak mediates Cdc42-signalling by being anchored to the neuronal membrane through the DsCAM/Dock complex. Keys to successful “bioprobing” are the mutation that freezes a protein’s affinity-delineating kinetics, transient expression that minimizes emergence of artifacts, and model neurons that allow in vivo image quantification. The design and usage of i-Probe are adoptable to studies on other proteins, cell types, and conditions, enabling novel imaging-based analyses on protein-protein interactions within intact cells and organisms.