Model Systems Research
ANKS1B haploinsufficiency
Principal Investigator: Dr. Bryen Jordan
We recently identified patients around the world harboring monogenic deletions of the ANKS1B gene with confirmed haploinsufficiency. Affected individuals present with a spectrum of neurodevelopmental phenotypes, including autism and speech and motor deficits. The long-term goal of the proposed research is to define the mechanisms underlying AnkSyd and to identify therapeutic targets. ANKS1B encodes for AIDA-1, a brain-specific protein that we have shown is enriched at neuronal synapses and regulates N-methyl-d-aspartate receptors (NMDARs) subunit composition and NMDAR-dependent synaptic plasticity.
Our immediate goals are to test the hypothesis that NMDAR dysfunction contributes to AnkSyd. Toward this purpose, we have generated induced pluripotent stem cells (iPSCs) and neurons from patients and unaffected family members, as well as a transgenic mouse model that displays behavioral correlates of patient phenotypes. Our objectives are to test NMDAR function in patient neurons, elucidate mechanisms linking AIDA-1 to NMDAR function, and identify disease-relevant molecular pathways underlying AnkSyd using a discovery-based approach. Our work has direct implications for human health and our understanding of synaptic function.
The role of GABAergic inhibition
Principal Investigator: Dr. Renata Batisto Barito
Recent evidence suggests disruption of GABAergic inhibitory function as a likely mechanism underlying autism. In order to function correctly, neural networks must establish precise and stable interconnected circuits. Synaptic refinement mediated by GABAergic inhibitory neurons during development is necessary for the precision of brain function, and thus, developmental disruption of GABAergic inhibitory neurons (also known as interneurons) has the potential to perturb fundamental cortical functions, such as accurate encoding of sensory information and higher-order cognition. Dysregulation of PV-interneurons has been suggested as a candidate mechanism underlying autism, but little is known about the mechanistic contribution of PV-interneurons to autism-related deficits. We use combination of approaches that includes mouse genetics, behavior, histology, synaptic physiology, in vivo electrophysiology, and transcriptomic analyses to test the hypotheses that Mef2c signaling shapes PV-interneuron development, and that age-specific Mef2c-related disruptions of PV-interneurons will impair different aspects of synaptic transmission and cortical activity, gaining mechanistic insights into how impaired PV-interneuron dysfunction can contribute towards autism symptoms.
Cerebellum and Autism
Principal Investigator: Dr. Kamran Khodakhah
The cerebellum has been implicated in a number of neurocognitive disorders such as autism , schizophrenia, and addiction. However, how it contributes to these disorders is not understood. In this proposal we explore whether the cerebellum sends direct excitatory projections to the ventral tegmental area (VTA), one of the brain regions that processes and encodes reward, and to the hypothalamus, a region implicated in social behavior. Using a combination of anatomical, functional (electrophysiology combined with selective optogenetic activation of cerebellar pathways), and behavioral studies we test the hypothesis that direct cerebellar projections to these two brain structures may be the substrate through which the cerebellum influences social behavior under physiological and pathological conditions. Defects in cerebellar modulation of the VTA and hypothalamus may explain, at least in part, how the cerebellum might contribute to disorders such as autism and schizophrenia. Thus, accomplishment of the goals set would not only advance our understanding of the non-motor functions of the cerebellum but may provide clues regarding the pathophysiology of a number of neurocognitive disorders.
Neuromodulatory control of the cerebellum – multisensory integration / behavioral flexibility
Principal Investigator: Stephanie Rudolph
As we navigate the world, we are confronted with a wealth of sensory information that we constantly have to detect, integrate, and filter to generate an appropriate behavioral response. How we respond requires the interplay of numerous brain regions, and depends on many factors, including the context in which a sensory stimulus occurred, previous experience, and internal state. We aim to identify the molecular, cellular, and circuit mechanisms that allow the cerebellum, an area of the brain that receives rich multisensory input, to dynamically respond to physiological context. We focus on the neuromodulatory systems involved in autonomic and metabolic regulation, social interactions, and sex-specific signaling. Using genetic and viral approaches, electrophysiology, and behavioral testing we examine the anatomical and molecular basis of neuromodulation in the mouse cerebellum, identify the circuit elements that respond to modulatory signals, and elucidate how this alters cerebellar output. Our ultimate goal is to better understand how context-dependent modulation of cerebellar function controls motor behavior, cognition, and emotion in health and disease.
Integrating, filtering, and prioritizing diverse sources of sensory information are essential to behavior. All of these aspects of multisensory processing are represented in the cerebellum, and it is thus not surprising that cerebellar dysfunction can lead to behavioral and emotional deficits, including social withdrawal, affective dysregulation, and anxiety. Consistent with these findings, the cerebellum has been implicated in many neurodevelopmental and psychiatric disorders, such as autism, ADHD, and schizophrenia. Therefore, understanding the mechanisms that enable the cerebellum to control behavior in a context-specific manner will be crucial to developing therapeutic interventions that restore normal cerebellar function, and ultimately the ability to adapt behavior.
Presynaptic forms of long-term plasticity
Principal Investigator: Dr. Pablo Castillo
Short and long-term activity-dependent changes in synaptic efficacy are essential to brain function. Experimental evidence indicates that activity-induced long-term potentiation (LTP) and long-term depression (LTD) of synaptic transmission are cellular correlates to learning and memory. growing evidence indicates that presynaptic LTP/LTD may underlie important forms of learning. However, the synaptic "learning rules" for these forms of plasticity are poorly characterized, and our understanding of presynaptic mechanisms lags far behind the postsynaptic side. Presynaptic plasticity can originate entirely in the presynaptic terminal or it may require retrograde signaling from postsynaptic to presynaptic compartments. In the last decade, retrograde signaling emerged as a widely expressed mechanism by which postsynaptic neurons can control their own inputs and, by this means, regulate neural circuits over short and long-time scales. The best characterized retrograde signaling system is the endocannabinoid (eCB) system, and while much has been learned from this system, important knowledge gaps remain for other retrograde messengers including the type of activity required for mobilization, the mechanisms of postsynaptic release and presynaptic action, and ultimately, the precise physiological role of retrograde signaling at a synapse in a given neural circuit. In this research proposal, we will address these outstanding questions by focusing on three distinct hippocampal synapses using state-of-the-art electrophysiology, molecular pharmacology, optogenetics, and live imaging in acute brain slices. Specifically, we will test the hypothesis that presynaptic protein synthesis is necessary for eCB-mediated LTD at inhibitory synapses. In addition, we will determine the mechanism and functional consequence of a novel form of presynaptic LTP at a key, but remarkably understudied, excitatory synapse in dentate gyrus. Finally, we will test the hypothesis that retrograde signaling negatively regulates a powerful "detonator" synapse. Knowledge derived from these investigations will provide new mechanistic insights on retrograde signaling at central synapses and may also uncover novel roles for presynaptic plasticity in the hippocampal network. A better understanding of presynaptic plasticity represents a significant step forward in the development of strategies to restore synaptic function in autism.
Altered synaptic structure and function is a hallmark of disorders characterized by Intellectual Disability (ID). Despite the identification of particular synaptic proteins that have been implicated in ID and Autism, the mechanisms by which defects in synaptic proteins lead to synapse dysfunction, and ultimately to neurodevelopmental disorders, are still largely unknown. We are studying two synaptic proteins in particular, the synaptic cell adhesion molecule Neurexin, which is highly associated with Autism, and the presynaptic voltage-gated calcium channel, a mutation in which was recently discovered in an IDDRC patient. We use the nematode C. elegans as a model system because of its highly tractable genetics and ease of experimental accessibility.
Neurexins are highly associated with Autism although their precise role at the synapse is increasingly being questioned. Long thought to be initiators of synapse development, recent evidence suggests they modulate synaptic function and plasticity, perhaps through interactions with other presynaptic proteins. However, neurexin’s intracellular presynaptic partners are largely unknown. To gain a better understanding of neurexin’s presynaptic signaling pathways we are undertaking an in vivo proximity ligation and proteomics approach using the newly-developed TurboID method.
We have recently shown that neurexin clusters calcium channels at the presynaptic terminal. Presynaptic calcium channels encoded by the CACNA1A gene in humans underlie synaptic transmission at nerve terminals and CACNA1A mutations have recently been linked to intellectual impairment and Autism. An IDDRC patient who presents with global developmental disabilities, seizures and ataxia was recently found to harbor a mutation in CACNA1A. The mutated residue is within a highly conserved region of the protein and is itself conserved all the way down to invertebrates, including C. elegans. Using CRISPR/Cas9 we have created C. elegans transgenic worms harboring this mutation and are using this strain to characterize the effects of this mutation on calcium channel localization and function, as well as on synaptic morphology and organismal behavior.
Metabotropic glutamate receptor functions in autophagy
Principal Investigator: Dr. Anna Francesconi
Abnormal maturation of brain circuitry during development is a critical determinant of pathological manifestations in neuropsychiatric conditions. A growing body of evidence from studies in human subjects and animal models has established a link between dysfunctions in glutamatergic neurotransmission and developmental brain abnormalities associated with these conditions. Group I metabotropic glutamate receptors are critical to formation and maintenance of brain circuitry and synaptic plasticity, a cellular substrate of learning and memory. We identified a new mGlu1-interacting protein, fasciculation and elongation protein zeta-1 (FEZ1) encoded by a schizophrenia candidate gene. Preliminary findings indicate that mGlu1 may function via FEZ1 to regulate autophagy in neurons. Autophagy is an evolutionarily conserved catabolic process critical to neuronal homeostasis and brain development. Autophagy is an evolutionarily conserved catabolic process critical to neuronal homeostasis and brain development. The proposed studies build on this progress to elucidate a fundamentally new mechanism by which group I mGluRs can contribute to regulation of neuronal homeostasis under physiopathological conditions. We propose to 1) determine the cellular mechanisms by which group I mGluRs regulate autophagy in neurons; 2) define the molecular pathways by which the receptors control autophagy initiation; 3) establish whether constitutively enhanced group I mGluR activity leads to autophagy impairment in an animal model of Fragile X syndrome; and 4) investigate the function of autophagy in group I mGluR-dependent remodeling of dendritic spines. Collectively, findings from these studies will significantly advance our understanding of the molecular and cellular substrates underlying metabotropic functions in the brain and build a molecular framework to understand cellular perturbations associated with synaptic pathologies in neurodevelopmental disorders.