http://www.hms.harvard.edu/dms/neuroscience/index.html
Associate Professor in Neurology
Dr. Bacskai's laboratory uses sophisticated optical techniques to address fundamental questions in Alzheimer's disease research. Using the imaging technique multiphoton microscopy, the senile plaques of Alzheimer's disease can be detected in the brains of living transgenic mice, and characterized with chronic imaging. By multiplexing with other structural and functional fluorescent probes, we can examine specific cellular responses to disease progression in vivo as well. This detection platform was used to characterize a therapeutic approach to clearing the senile plaques based on immunotherapy, as well as to characterize movel amyloid-targeting ligands in preclinical development for PET imaging in humans. Current research is aimed at optimizing anti-amyloid-ß therapeutic approaches, and imaging the anatomy and physiology of specific cell types in the brain before and after treatment. Development of novel optical techniques is ongoing, and includes methods to measure protein-protein interactions using fluorescence lifetime imaging microscopy (FLIM), and non-invasive approaches to amyloid imaging in intact animals based on NIR fluorescence diffuse optical tomography.
Professor of Psychiatry (Neuroscience)
Dr. Benes pioneered the application of rigorous quantitative approaches to characterize anomalies in the circuitry involving anterior cingulated (ACCx), hippocampus (HIPP) and basolateral amygdale (BLa). Her research program uses a two-pronged approach in which postmortem studies of limbic lobe structures are conducted in parallel with a rodent model for the neural circuitry changes observed in the anterior cingulated cortex and hippocampus of schizophrenic and bipolar subjects. Usina a broad array of microscopic (double and single in situ hybridization), molecular (laser capture microdissection (LCM), microarray-based gene expression profiling (GEP), quantitative RT-PCR) in postmortem and rodent studies, her lab has been systematically delineating how GABA cell dysfunction in amygdalo-hippocampal circuitry contributes to the pathophysiology of psychotic disorders. Additionall, patch clamping approaches are also used to assess the electrophysiological properties of GABA cells following amygdalae activation in awake, freely moving rats. Specifically, excessive glutmatergic activity from the BLa seems to induce dysfunction of GABA cells in layer II of the ACCx and sectors CA3/2 of the hippocampus, two sites that receive a rich innervation from this nucleus. During postnatal development, results in changes in GABA cells that remarkably dimilar to those seen in SZs and BDs. Gaba cell dysfunction seems to be further exacerbated by the ingrowth of amygdalar and dopamine afferents during the postnatal period as they form functional interactions with GABAergic interneurons. It is believed that these developmental changes may help “trigger” the onset of schizophrenia during late adolescence and early adulthood. Dr. Benes’ laboratory is currently defining the cellular endophenotypes for SZ and BD using LCM, GEP and sophisticated network association analyses of functional genetic pathways.
Associate Professor of Pathology
We are interested in the signaling and transcriptional mechanisms that regulate cell survival and differentiation in the mammalian brain and how abnormalities of these pathways contribute to neurologic disorders. We have begun to elucidate the intracellular mechanisms that specifically regulate the development of axons and dendrites in granule neurons of the developing mammalian cerebellum. We have identified a novel function for the transcription factor NeuroD in the specification of dendrites. We have also defined a CaMKII-NeuroD signaling pathway that mediates neuronal activity-dependent dendritic growth. It will be important to determine how the CaMKII-induced phosphorylation of NeuroD at key sites including Serine 336 regulates NeuroD function, to identify targets of NeuroD that specifically promote dendritic growth, and to determine if NeuroD is the target of other extrinsic signals that regulate dendritic growth.
Professor of Neurology
Our laboratory uses molecular genetic and imaging methods to gain insight into the molecular etiology of early onset torsion dystonia, and to develop vectors and strategies for gene therapy of brain tumors and neurologic diseases.
Torsion dystonia is a movement disorder characterized by contracted postures of the limbs and torso due to abnormal circuitry in the basal ganglia affecting sensori-motor communication. The mutant protein responsible for most early onset cases encodes torsinA, a AAA+ protein localized primarily in the endoplasmic reticulum (ER). This protein is expressed at highest levels in the perinatal period in neurons and appears to act as a chaperone protein involved in processing of proteins through the secretory pathway and linking the ER to the cytoskeleton. Current studies focus on identifying interacting partners for torsinA and determining how the mutant protein disrupts cell adhesion, neurite extension and synaptic communication.
Vectors derived from HSV, AAV and lentivirus are used to deliver therapeutic genes and imaging reporters in mouse models of inherited neurologic dieases, i.e. ataxia telangiectasia and neuronal ceroid lipofuscinosis, and brain tumors, including glioma xenografts and Cre-lox-induced loss of tumor suppressor genes, i.e. neurofibromatosis type 2 and tuberous sclerosis. Therapeutic strategies include expressing biotinylated docking sites on the cell surface to bind streptavidin-toxin conjugates using neuroprecursor cells to home to invasive tumor cells, and regulating microRNA levels to inhibit angiogenesis.
Associate Professor of Neurology
Neuron-glia interactions play critical roles in several aspects of nervous system development, including neuronal migration, neuronal and glial differentiation and survival, and the formation and function of synapses. We are primarily interested in understanding the molecular signals that regulate neuron-glia interactions and their roles. To this end, we are using molecular and cellular biological techniques, as well as genetically modified mice.
Part of our work focuses on the growth factor neuregulin (NRG) and its erbB receptors, key mediators of neuron-glia interactions. We have found that these molecules mediate interactions between migrating neurons and the radial glial fibers along which they migrate during the development of the central nervous system, and between several types of glia and neurons in the adult nervous system.
We are interested in the gating of mechanically sensitive ion channels, which open in response to force on the channel proteins. We study these channels primarily in vertebrate hair cells -- the receptor cells of the inner ear, which are sensitive to sounds or accelerations. Hair cells are epithelial cells, with a bundle of stereocilia rising from their apical surfaces. Mechanical deflection of the bundles changes the tension in fine filaments (tip links) that stretch between the stereocilia; these filaments are thought to pull directly on the mechanically gated transduction channels to regulate their opening. In earlier work, we found that cutting these links immediately and irreversibly abolishes the mechanical sensitivity, consistent with the model. We also used calcium imaging to locate the transduction channels (which pass calcium as well as other cations) and found that they can be at both ends of the tip links.
Hair cells have a "slow" adaptation mechanism, which acts to maintain a constant tension in each tip link. Manipulations that change the rates of adaptation cause the bundle to move, by up to 100 nanometers, supporting the idea of an active motor mechanism. This is thought to be a complex of 10-30 myosin molecules just under the membrane at each end of each tip link. In order to identify a candidate for the motor myosin, we cloned fragments of most of the myosins expressed in hair cells. We found one of these, myosin-1c, to be located at the tips of stereocilia, specifically at the ends of tip links. Inhibiting the function of myosin-1c with engineered inhibitors blocks adaptation. A second, faster form of adaptation results from Ca++ entering through transduction channels, binding to an intracellular site on the channel, and closing it. With optical trap measurements of bundle mechanics, we found that a Ca++-bound channel requires about 3.5 picoNewtons more force to open than an unbound channel.
To identify the transduction channel itself, we carried out a screen of the TRP channel superfamily, by finding all TRP channels in the mouse genome and looking for inner ear expression with in situ hybridization. Several TRPs are expressed in the inner ear, and RT-PCR showed that expression of one, TRPA1, rises just before hair cells become mechanically sensitive. Antibodies to TRPA1 label the tips of stereocilia. Inhibiting expression of the channel--with morpholino oligonucleotides in zebrafish, or with siRNA-encoding adenovirus in mouse--inhibited hair cell function. We are now focusing on this channel and its linkage to other components of the transduction apparatus.
Associate Professor of Pathology
The molecular mechanisms underlying neurodegeneration in human disorders like Alzheimer’s disease and Parkinson’s disease remain largely mysterious, in part because genetic analysis in patients and vertebrate models is laborious. Disease models in simpler organisms, like Drosophila, harness the power of genetics to define cellular pathways underlying the specific destruction of postmitotic neurons in neurodegenerative disorders. In our laboratory we have created fruit fly models of several human diseases, including Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis (Lou Gerhig’s disease), and spinocerebellar ataxia type 1 (a disease produced by expanded polyglutamine repeats). Mutations in the a-synuclein gene cause familial Parkinson’s disease, and a-synuclein protein accumulates in intraneuronal inclusion bodies in both familial and nonfamilial Parkinson’s disease. By expressing normal and mutant human a-synuclein in flies, we have recreated key features of the human disorder: dopaminergic neurodegeneration, intracytoplasmic neuronal inclusion bodies containing a-synuclein, and progressive locomotor dysfunction. We have taken similar approaches to modeling Alzheimer’s disease, amyotrophic lateral sclerosis, and polyglutamine disorders in Drosophila. Genetic screens have been performed in these models to define the cellular pathways mediating neurodegeneration. Our results so far support a critical role for posttranslational modifications such as phosphorylation in modulating protein aggregation and neurotoxicity in our models. Candidate mediators defined in the Drosophila models are being investigated in mammalian systems, including human disease, to evaluate the role of the proteins in the pathogenesis of human neurodegenerative disorders.
Professor of Cell Biology
Our broad interest is to understand how cell-cell signaling molecules establish spatial pattern, particularly in the development of neural connections. Approaches include identification of novel signaling molecules, and functional analysis by molecular, cellular, genetic and embryological methods.
Identification of novel cell-cell signaling molecules. Using soluble receptor techniques developed in this lab, we identified some of the first members of a family of cell-cell signaling molecules, the ephrins, which have unique functions in neural development. We continue to develop and apply such techniques to identify other signaling molecules that should open up new areas of biology.
Wiring up the nervous system: cues for pathway selection and topographic mapping. During development, projecting axons first find their target regions by pathway selection. Then, within the target, axons typically form topographic maps, where the spatial arrangement of the projecting neurons is maintained in the order of their connections. We are interested in how the complex pattern of axonal pathways and maps is specified by extracellular guidance cues. Recent projects include dynamic regulation of pathfinding behavior in axons as they cross the spinal cord midline; and ephrins as graded labels specifying position in neural maps.
Molecular mechanisms for cellular interpretation of guidance information. We are also interested in intracellular signaling mechanisms, including downstream pathways that convert extracellular cues into an appropriately polarized cell response, and upstream mechanisms that regulate how axons respond to cues, including switches in responsiveness as growing axons reach intermediate and final targets. One class of mechanisms we are especially interested in currently are local protein translation and RNA-based control mechanisms within axons.
Associate Professor of Neurobiology
We are interested in the development of neural circuits, from the determination and differentiation of neurons to the formation of axonal connections and ultimately the generation of behavior. The auditory and vestibular systems, which are both housed in the ear, provide an exciting opportunity to link development to the function of neural circuits, since these systems are closely related developmentally, but in the adult, control the distinct behaviors of hearing and balance. Moreover, despite the obvious impact that congenital and age related hearing loss have on society, little is known about the genetic mechanisms that underlie development and function of the ear.
Our research program explores 3 major topics: Patterning in the Ear and Hindbrain; Circuit Formation; and Auditory/Vestibular Behavior. We address questions such as what cellular and molecular cues ensure the vestibular-auditory division of the developing otic vesicle? how are tonotopic maps preserved at each level of the auditory system? and how do changes in patterning or wiring affect auditory or vestibular system function?
We are using the mouse as a model system, taking advantage of recent exciting advances in mouse genetic technology, especially a gene trap mutagenesis approach that allows us not only to mutate genes, but also to label the neurons that express the mutated genes, including even the complete axonal trajectory of each neuron. In addition, we use a variety of molecular and physiological approaches including in situ hybridization, microarray analysis of normal and mutant mice, and Auditory Brainstem Response recordings to analyze hearing in mutant animals. To complement the work in mice, we also perform studies in chick embryos and design in vitro assays that allow us to best explore questions of both cell fate and axon guidance.
Assistant Professor of Neurobiology
Nervous and vascular systems share many features, despite their distinct functions. Developmentally, they are formedaround the same time, and both continue to dynamically remodel throughout life. Anatomically, they are both highly-branched and complicated networks; yet both networks have remarkably stereotyped patterns. Moreover, even from thetime of Vesalius and Da Vinci, it has been clear that nerves and vessels often run adjacent to each other. Functionally,neural activity and vascular dynamics are interdependent in the periphery and tightly coupled in the brain. Despite theimportance of this intimate relationship, little is known at the molecular level about how these two systems are coordinatelypatterned during development and what permits ongoing neurovascular interactions in the adult. The goal of our research isto understand the molecular mechanisms of how neural and vascular networks are coordinately developed, communicate,and evolve to work in concert during normal and disease states.
Using a combination of mouse genetics, cell biology, and biochemistry-based approaches, our research program currentlyexplores 4 topics: 1. Characterize the intriguing neurovascular anatomical relationship in the brain. 2. Identify the molecularsignaling cascade controlling neural and vascular patterning and their intercommunication. 3. Identify novel factors fromendothelial cells that control neuronal function and vice versa. 4. Address how patterning cues influence human disease,involving both neural and vascular damage and repair. To study these questions in vivo, we frequently use geneticallyengineered mouse models with specific mutations and tracers combined with imaging and physiological approaches. Tocomplement this work, we also perform studies in chick and a variety of in vitro assays to further reveal the mechanisms ofaction. With these approaches, we aim to understand the neurovascular interactions from a molecular level to a systems level.
Associate Professor of Neurology
We are interested in understanding the cellular and molecular mechanisms involved in axon degeneration and regeneration.
Failure of successful axon regeneration in the CNS is attributed not only to the intrinsic regenerative incompetence of mature neurons, but also to the environment encountered by injured axons. We are interested in exploring the mechanisms for both environmental inhibitory influences and intrinsic regenerative capacity. Previous studies indicate that the inhibitory activity is principally associated with components of CNS myelin and molecules in the glial scar at the lesion site. Recent studies from our laboratory and others suggested that three myelin proteins, myelin-associated glycoprotein (MAG), Nogo-A and oligodendrocyte myelin glycoprotein (OMgp), collectively account for the majority of the inhibitory activity in CNS myelin. The inhibitory activity of MAG, OMgp and the extracellular domain of Nogo-A might be mediated by a receptor complex with a Nogo receptor and at least two co-receptors, p75/TROY and Lingo-1. Our current studies are aimed to define signaling pathways that transduce these inhibitory signals to cytoskeleton. In addition, we are also actively studying the cellular and molecular mechanisms underlying the intrinsic regenerative capacity of mature neurons. All of these studies are carried out in a combination of in vitro and in vivo approaches.
Axon degeneration occurs frequently in physiological neuronal remodeling and pathological neurodegeneration. We have been using Wallerian degeneration as a model to explore the cellular and molecular mechanisms of axon degeneration. It is hoped that this line of study will provide insights into the mechanisms of brain aging and neurodegenerative diseases.
John B. Penney, Jr. Professor of Neurology
Dr. Hyman’s laboratory studies the anatomical and molecular basis of dementia in Alzheimer’s disease and dementia with Lewy bodies. Approaches focus on transgenic mouse models and human neuropathological samples, using advanced microscopy techniques for in vivo longitudinal imaging, direct imaging on neuropathological processes including cell death, and functional imaging including in vivo assessment of calcium reporters. Quantitative approaches have been developed to apply to clinical pathological and genotype/phenotype analyses. Recent studies have developed the use of multiphoton microscopy for in vivo anatomical and functional imaging in transgenic mouse models of Alzheimer's disease and the utilization of gene transfer techniques to introduce potentially disease-modifying genes into specific cortical regions. We have also developed fluorescence resonance energy transfer (FRET) approaches to allow observation of protein-protein interactions with subcellular resolution, both in vitro and in vivo. These techniques are utilized to examine the alterations that occur in Alzheimer's disease brain, and in mouse models expressing genetic mutants that are linked to Alzheimer's disease.