October 9th - Supplementing Imaging with Stimulation: Insights from Combining Transcranial Magnetic Stimulation with fMRI and EEG
Behavioral neuroscientists are taught from an early stage that physiological measures provide "only" correlational information about brain-behavior relationships, whereas methods that alter normal function can support stronger inference about the necessity of a region's contribution to the behavior of interest. This talk will illustrate several realizations of this dictum. First, repetitive (r)TMS has confirmed and refuted different models of prefrontal cortex function that are based on fMRI data. In the process, it has highlighted limitations inherent in the practice of group averaging fMRI data. Second, applying TMS during fMRI scanning provides novel insights about the blood oxygen level-dependent (BOLD) response that fMRI measures. Third, applying rTMS during EEG recording provides novel insights about the functional role of cortical oscillations measured by the EEG.
November 13th - Reinventing the Wheel: Using FRET Imaging to Determine the Holoenzyme Structure of CaM Kinase-II in Living Cells
CaM kinase II is one of the most abundant proteins in the brain, and is highly enriched in post-synaptic densities. It is known to play a pivotal role in integrating calcium influx signals in post-synaptic spines, in mediating long term potentiation, and for spatial learning tasks. CaM kinase II is activated upon binding calcium calmodulin, and can become persistently activated by an auto-phosphorylation mechanism. Its ability to integrate calcium signals is believed to be an emergent feature of auto-phosphorylation in conjunction with its holoenzyme structure. CaM kinase II is thought to assemble into a multimeric 'wheel-like' structure composed of 12 kinase subunits. Several different models have been proposed for the holoenzyme structure based on in vitro analysis, but little is known about its structure in living cells. Förster resonance energy transfer (FRET) is a physical phenomenon where an excited fluorophore (the 'donor') can transfer energy to a nearby chromophore (the 'acceptor') via non-radiative dipole-dipole coupling. The distance that energy can be transferred is typically under 10 nm. Thus, FRET can be used to measure the proximity of fluorophores on a nanometer scale. With the advent of spectral variants of Green Fluorescent Protein (FPs) it is now possible to genetically tag proteins of interest and use FRET imaging to monitor protein-protein interactions in living cells. The fraction of energy transferred from an excited donor to acceptors is called the FRET efficiency and can be measured by several methods. In this study we use two FRET methods, fluorescence anisotropy analysis and sensitized acceptor emission to elucidate the structure of CaM kinase II in living cells, and to monitor structural changes that correlate with enzyme activation.
December 11th - Mapping Human Brain Tumors Using Physiological MRI
This talk will describe how physiologic magnetic resonance imaging (MRI) methods can be integrated to more accurately define and delineate glioblastoma multiforme (GBM) brain tumors in preparation for radiation therapy treatment. We hypothesize that the use of these imaging modalities will result in a significant improvement to the precision of the radiotherapy treatment plan. Data will be presented to indicate that chemical shift imaging (CSI), perfusion and diffusion imaging and MR-based hypoxia mapping add additional information about tumor physiology that can be incorporated into a treatment plan with the goal of decreasing the rate of tumor recurrence. Although regions of abnormality on anatomical MRI’s are known to correlate with microscopic spread of tumor, some of this abnormality represents edema without malignant cells, yet other areas may contain a high concentration of malignant cells that should be incorporated into the treatment boost volume. Physiologic processes are likely identified by more than one MRI parameter, thus by considering voxels indicated as abnormal by more than one technique, more specific, reliable overlap maps can be created. A single descriptive overlap map could be used to identify “high-risk subvolumes” within each tumor, which may be at high risk of recurrence. Clinically, our goal is that after completing radiotherapy, patients will be followed with serial physiologic MRI scans; the study endpoint being the first recurrence. The location of the recurrence(s) will be compared with the delivered radiation treatment plan and the experimental “high-risk subvolume.” If the out-of-field recurrences are predicted based on the advanced imaging results, future phase II trials using physiologic imaging could be undertaken with local control being the endpoint. Conversely, recurrences may occur within the treatment fields, but in regions that are intrinsically radioresistant such as hypoxia or high proliferative potential. The MRI methods should help to identify these regions, and if so, may allow for future trials of selective dose escalation to these areas of resistance.
February 26th - Imaging Bioinformatics: Is an Image Worth a Thousand Experiments?
March 11th - Stem Cells, Wnt Signaling and Mammary Tumor Development
We are studying aspects of mammary gland biology and neoplasia using transgenic mouse models. Particularly, we have found that Wnt signaling dysregulates mammary stem cells, and that this precedes the formation of differentiated, bilineal tumors. Wnt signaling is highly oncogenic to mammalian epithelia, and indeed comprises one of the main sources of human tumor initiation identified to date. Our hypothesis is that the transforming potential of Wnt signaling is unique to stem/progenitor cells. Our work aims at elucidating how and when adult somatic stem cells can be recruited as tumor precursor cells.
April 18th - Single-Molecule and Super-Resolution Imaging of Biomolecules and Cells