2009 — 2013 |
Bai, Jihong |
K99Activity Code Description: To support the initial phase of a Career/Research Transition award program that provides 1-2 years of mentored support for highly motivated, advanced postdoctoral research scientists. R00Activity Code Description: To support the second phase of a Career/Research Transition award program that provides 1 -3 years of independent research support (R00) contingent on securing an independent research position. Award recipients will be expected to compete successfully for independent R01 support from the NIH during the R00 research transition award period. |
Mechanisms of Synapse Remodeling @ Massachusetts General Hospital
DESCRIPTION (provided by applicant): Synapse remodeling is the process of forming and eliminating synapses to reorganize the existing brain circuitry, and is indispensable for establishing and maintaining the integrity of the nervous system. Synapses are constantly remodeled throughout the lifetime of an animal. Remodeling peaks in the juvenile nervous system, levels off throughout adulthood, and declines with senescence. The long-term goal of my research is to identify the signaling pathways and molecular machinery that mediate synapse remodeling. This will help us to understand how synapses are formed and eliminated at the right time and right place, and provide fundamental information towards our ultimate goal of understanding and treating numerous neurological diseases and mental disorders. To approach analysis of synapse remodeling at the molecular level, it is informative to begin with a simple invertebrate model. In C. elegans, synapse remodeling occurs in a reliable and predictable manner during development. At the end of the first larval stage, 6 motor neurons reverse their axon-dendrite polarity, disassemble existing synapses, and form new ones in a distant location. This simple rewiring process provides an excellent model system that is accessible to both molecular manipulation and in vivo optical observation. The objective of my proposed research is to investigate the molecular pathways defining the timing of synapse remodeling and to identify new genes involved in switching the identity of the synapses. This application includes the following aims: first, I will investigate temporal regulation of synapse remodeling, testing the hypothesis that genes responsible for controlling the sequence of developmental events (heterochronic genes) regulate synapse remodeling. Second, I will combine data from microarray analysis, a RNAi screen and a forward genetic screen to identify new factors required for synapse remodeling. Finally, a novel quantitative imaging analysis approach will be used to determine spatial regulation of the ubiquitin-proteasome system mediating degradation of synaptic components during synapse remodeling. Together, the experiments outlined in this application will provide a mechanistic understanding of synapse remodeling and its regulation.
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2013 — 2017 |
Bai, Jihong |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Membrane Bending Machinery For Synaptic Vesicle Endocytosis @ Fred Hutchinson Cancer Research Center
Abstract: Brain activity is driven in large part by neurotransmitter secretion, which is derived from a small pool of recycling synaptic vesicles (SVs). Following exocytosis, membrane and protein components of synaptic vesicles are incorporated into the plasma membrane and must be retrieved by endocytosis to maintain continued synaptic function. Subtle changes in SV endocytosis can lead to severe defects in brain function. The long-term goal of this project is to determine the molecular mechanisms governing SV endocytosis. Here, we will investigate Endophilin, a conserved protein required for SV endocytosis. In preliminary studies, we showed that Endophilin promotes endocytosis by bending membranes whereas its function as a molecular scaffold is not required for endocytosis. We showed that the majority of Endophilin at nerve terminals is bound to SVs, not at endocytic sites. We further showed that the rate of Endophilin unbinding from SVs is regulated by exocytosis. Based on these preliminary results, we propose three Aims. In Aim 1, we develop real-time assays for Endophilin's membrane association, oligomerization, and membrane bending. We will use these assay to determine if the rate of membrane bending is sufficiently fast to account for Endophilin's function in endocytosis. In Aim 2, we will determine how Endophilin is targeted to SVs. We hypothesize that inactive Endophilin monomers bind to the SV protein RAB-3 and thereby recruit Endophilin to the SV pool. We will use biochemical, genetic, and imaging approaches to test this idea. We will also determine if phosphatidylinositol 4,5-bisphosphate (PIP2) stimulates Endophilin oligomerization at endocytic sites. In Aim 3, we will determine how Synaptojanin's PIP2 phosphatase activity is coupled to endocytosis. Specifically, we will define the molecular mechanisms that allow Synaptojanin to sense membrane curvature generated by Endophilin. These studies will provide significant new insights into the mechanisms regulating SV endocytosis and how BAR domain proteins function generally.
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2018 — 2019 |
Bai, Jihong |
R21Activity Code Description: To encourage the development of new research activities in categorical program areas. (Support generally is restricted in level of support and in time.) |
Genetic Dissection of Circuit Modulation For Cross-Modal Plasticity @ Fred Hutchinson Cancer Research Center
Project Summary/Abstract The brain is wired to integrate data from multiple sensory inputs, and is highly dynamic and amenable to plasticity and reorganization. Our long-term goal is to understand the molecular mechanisms that coordinate different brain circuits and govern brain-wide plasticity. In particular, we are interested in cross-modal plasticity that occurs following the loss of a sensory modality, due to disease or injury, and leads to enhanced performance of remaining sensory modalities. However, in addition to positive adaptive outcomes, cross-modal plasticity might also have negative impacts on sensory acuity and precision. Cross-modal plasticity has been studied extensively at the macroscopic level of brain structures in mammalian brains. In contrast, molecular pathways that produce opposing outcomes upon sensory deprivation are much less known. We have recently discovered a form of cross-modal plasticity in the simple nervous system of C. elegans, which presents an opportunity to genetically trace the molecular basis for cross-modal plasticity. Our data show that loss of body touch sensation increases olfactory acuity towards a certain class of odors. The underlying molecular pathway shares striking similarities with analogous mammalian systems. We were able to counteract the observed plastic changes using a synaptic engineering approach. We also found that in parallel to the adaptive increase in olfactory performance, loss of body touch sensation resulted in a concomitant decrease in olfaction towards a second group of attractive odors and to a reduced response to mechanical stimulation of the nose. Here, we propose to explore the molecular constituents of cross-modal plasticity using genetic manipulations in C. elegans. Our goal is to identify system- wide interactions with both positive and negative impacts across multiple sensory modalities. We will address several fundamental questions. What are the molecular determinants that lead to opposite behavioral outcomes? Are they independent or do they interact? We will examine these questions using genetics, behavioral assays, calcium imaging, optogenetics, and synaptic engineering. Delving into the molecular mechanisms underlying cross-modal plasticity and especially into the manner in which various forms of cross-modal plasticity interact will provide new molecular insights into plasticity from a system-wide perspective, and promises to introduce potential avenues for intervention in sensory loss disorders.
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2018 — 2021 |
Bai, Jihong |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Molecular Mechanisms That Control the Quality of Synaptic Vesicle Recycling @ Fred Hutchinson Cancer Research Center
Project Summary/Abstract (from parent grant) Neuronal communication underpins all cognitive and physical activities (i.e., movement, perception, learning, and memory). High quality communication is essential to maintain organism homeostasis and disruptions lead to severe consequences. Synaptic vesicles (SVs) store and release neurotransmitters and serve as morphological counterparts of the neurotransmitter quanta. Thus, both morphology and function of SVs have significant implications in the quantal information transmitted from one neuron to another. The activity of SVs is highly dynamic. Upon arrival of Ca2+ signals, SVs fuse with the plasma membrane and release their neurotransmitter content through exocytosis. After exocytosis, SVs are incorporated into the plasma membrane and then must be retrieved into newly formed vesicles by SV endocytosis. This SV recycling is one of the best-orchestrated biological processes known, and at the same time, many of the intricate mechanisms that govern recycling remain unknown. It is imperative to gain a grasp of the mechanisms as scientific research recognizes that defects in vesicle property creates deficits in synaptic transmission, a common failing that underlies various forms of neurological and psychiatric disorders. The long-term goal of our work is to elucidate the fundamental mechanisms underlying effective neuronal communication by ensuring quality of SVs. AP180, a 180-kD adapter protein isolated from brain tissues, has been identified as a critical presynaptic protein and major component of clathrin-coated vesicles. AP180 has been implicated in human psychiatric and neurodegenerative disorders including schizophrenia and Alzheimer?s disease. Genetic data demonstrate that AP180 has crucial roles in controlling the morphology and protein composition of SVs and its disruption causes synaptic defects in worms, fruit flies, and mice. Using the nematode C. elegans as a model system, we plan to investigate and firmly establish the role of AP180 in maintaining both morphological and functional integrity of SVs in this project. We will design and employ state-of-the-art genetics, cell biology, biochemistry, and electrophysiological techniques to dissect the role of AP180. The proposal has three specific aims and addresses 1) the central role of AP180 in a two-step mechanism for SV recycling, 2) the intriguing activity- dependent regulation of AP180 dynamics at the synapse, and 3) the AP180-dependent mechanism that controls the size of SVs. We have built our hypotheses on solid knowledge base; our incisive methodologies have strong prospects to yield deep insights into SV recycling. The knowledge gained on the function, dynamics, and specificity of AP180 has broad ramifications in synaptic activity and brain function. Together, our studies hold promise to push boundaries of the current knowledge of synaptic transmission and broaden horizons with a strong potential to unravel the neurological intricacies and invent solutions for neurological disorders.
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2020 — 2021 |
Bai, Jihong |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Membrane Curvature Sensing Mechanisms For Synaptic Vesicle Endocytosis @ Fred Hutchinson Cancer Research Center
Project Summary Endocytosis plays a crucial role in supporting the health of the human brain. Functionally, synaptic vesicle endocytosis allows neurons to sustain synaptic transmission without exhausting the supply of synaptic vesicles. Structurally, endocytosis supports the maintenance of synapses and neural circuits. As a result, defective synaptic vesicle endocytosis creates deficits in neurotransmission that underlie a wide spectrum of neurological diseases and psychiatric disorders. The long-term goal of this study is to determine how endocytic proteins act in concert to support diverse routes of endocytosis at synapses. Work from several laboratories including my own has found that the curvature-sensing protein endophilin plays a critical role in synaptic vesicle endocytosis. In this proposal, we will examine the hypothesis that curvature-sensing mechanisms guide endocytic proteins to perform their function in various routes of endocytosis. We propose three Specific Aims. 1) We will determine the role of curvature-sensing motifs in vivo. We focus on the curvature-sensing amphipathic helix of endophilin as it is essential for synaptic vesicle endocytosis. 2) We will study how curvature signals are received by the downstream protein synaptojanin to support synaptic vesicle endocytosis, and to prevent age-dependent decay of synaptic transmission. 3) We will determine the mechanism of endophilin-independent endocytosis, an area that lacks molecular information. Through an unbiased genetic screen, we have identified another curvature-sensing protein that acts in a parallel pathway with endophilin. Results from these studies are expected to to push boundaries of current knowledge of synaptic biology and to lead toward solutions for neurological disorders.
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