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Cellular and Molecular Mechanisms of Synaptic Specificity

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Cellular and Molecular Mechanisms of Synaptic Specificity University of Calgary PRISM: University of Calgary's Digital Repository Graduate Studies The Vault: Electronic Theses and Dissertations 2016 Cellular and Molecular Mechanisms of Synaptic Specificity Getz, Angela Getz, A. (2016). Cellular and Molecular Mechanisms of Synaptic Specificity (Unpublished doctoral thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/25237 http://hdl.handle.net/11023/3466 doctoral thesis University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission. Downloaded from PRISM: https://prism.ucalgary.ca UNIVERSITY OF CALGARY Cellular and Molecular Mechanisms of Synaptic Specificity by Angela Michelle Getz A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY GRADUATE PROGRAM IN NEUROSCIENCE CALGARY, ALBERTA NOVEMBER, 2016 © Angela Michelle Getz 2016 Abstract All nervous system functions rely upon the specificity of synapse formation and maturation, and the experience-dependent remodeling of established synapses. Activity- and neurotrophic factor (NTF)-dependent signaling events guide the appropriate expression and localization of various components of pre- and postsynaptic machinery to ensure synaptic network function is matched to the behavioral requirements of an animal. These processes govern the function of the individual synapses formed by any given neuron, although the underlying cellular and molecular mechanisms have not been fully defined. To determine postsynaptic mechanisms of synaptic specificity, I investigated the role of menin, the product of the MEN1 tumor suppressor gene, in promoting cholinergic postsynaptic function in response to NTFs. Here, I present the first direct evidence for the molecular actions of menin in neurons, which coordinates the selective transcriptional upregulation and postsynaptic clustering of neuronal nicotinic acetylcholine receptors (nAChR). This occurs through distinct actions of proteolytic fragments generated by activity-dependent calpain cleavage. These data identify a novel synaptogenic mechanism for the coordination of nuclear transcription and postsynaptic localization of neurotransmitter receptors by a single gene product, and identify menin as a candidate molecular scaffold for neuronal nAChR clustering. To determine presynaptic mechanisms of synaptic specificity, I investigated how a co-transmitting neuron selectively employs classical or peptide neurotransmitters at synapses with distinct postsynaptic targets. Here, I present the first evidence that the function of individual presynaptic ii terminals is differentiated in a target cell-specific manner by an interplay between NTF and retrograde arachidonic acid signaling. I found that presynaptic transmitter specificity was defined by regulated synaptophysin expression, which selectively inhibited neuropeptide release machinery. These observations identify a novel role for synaptophysin in the regulation of peptidergic synaptic transmission, and a new component of NTF-dependent synaptic plasticity through which the co-transmitter characteristics of individual presynaptic terminals are regulated. Together, these studies delineate novel mechanisms underlying activity- and NTF-dependent synaptic specificity, underscoring the importance of appropriate expression and localization of synaptic machinery in controlling neuronal network function via the specialization of individual synapses. These findings provide fundamental mechanistic insights into the neurodevelopmental, neuropsychiatric, and neurodegenerative disorders in which these processes are disrupted. iii Acknowledgements To my supervisor, Dr. Naweed Syed – thank you for teaching me to be an experimentalist, to find wonder and humility in science, and for always giving me the freedom and encouragement to explore whatever observation peaked my curiosity. To my committee members, Dr. Gerald Zamponi and Dr. Michael Colicos – thank you for providing the guidance, experimental insights, and fresh perspectives necessary to develop and realize these ideas. To Wali – thank you for your tireless dedication to the craft, and for always making my increasingly demanding cell culture requests a reality. To Frank – thank you for teaching me everything I know about molecular biology, and for always encouraging me to take a step back, and then try something new. To the past and present members of the Syed lab, especially Fenglian, Collin, Tara, Pierre, Svetlana and Jean – thank you for your collaboration and friendship along the way, for sharing in the excitement and frustration that comes with science, and for always making day to day life in the lab amusing. iv To my parents, Susan and Darrell – thank you for your endless support, for encouraging me to pursue my dreams even when it means moving away from you, and for both uniquely prompting a lifelong curiosity in how and why the brain does what it does, which has given me direction in life. To my incredible family and friends back home in Regina – thank you for giving me perspective in life, and for always being there for me, no matter the distance. To the wonderful friends I have made during my time in Calgary – thank you for all the good times over the past decade, and for making this city my new home. To Tobi – thank you for being a true partner in life, and for your limitless curiosity and sense of adventure that parallels my own. Thank you for your patience and understanding, for your support and encouragement, and for always walking the dog when I was feeling overwhelmed while writing up. v Table of Contents Abstract ............................................................................................................................... ii Acknowledgements ............................................................................................................ iv Table of Contents ............................................................................................................... vi List of Tables .......................................................................................................................x List of Figures and Illustrations ........................................................................................ xii List of Symbols, Abbreviations and Nomenclature ...........................................................xv Epigraph ........................................................................................................................... xxi CHAPTER ONE: INTRODUCTION ..................................................................................1 1.1 General Introduction ..................................................................................................1 1.2 Synaptic Transmission ...............................................................................................3 1.2.1 Chemical synapses: neurotransmitters and neurotransmitter receptors .............3 1.2.2 Chemical synapses: specificity of transmission at the presynaptic terminal .....5 1.2.3 Chemical synapses: specificity of transmission at the postsynaptic terminal ...8 1.3 Synapse Formation ..................................................................................................10 1.3.1 Intrinsic signaling: the ‘ready-set-go’ model of synaptogenesis .....................10 1.3.2 Cell-cell signaling: cell adhesion molecules induce synaptic differentiation .11 1.3.3 Cell-cell signaling: neurotransmitter-receptor interactions .............................13 1.3.3.1 Cell-cell signaling: ‘black-box’ factors – peptide neurotransmitter- receptor interactions ................................................................................15 1.3.4 Extrinsic signaling: neurotrophic factors .........................................................16 1.3.5 Extrinsic regulation of intrinsic signaling: genetic foundations of synaptogenesis .................................................................................................18 1.3.5.1 Activity-dependent gene expression ......................................................19 1.3.5.2 NTF-dependent gene expression ...........................................................21 1.3.5.3 Signal integration: coincidence detection ..............................................22 1.3.5.4 Signal integration: ‘black-box’ factors – the MEN1 gene .....................23 1.4 Synaptic Specificity .................................................................................................25 1.4.1 Cell-cell signaling: the ‘chemoaffinity’ model of synaptic specificity ...........25 1.4.2 Signal integration: mechanisms that specify the function of individual synapses ...........................................................................................................26 1.4.2.1 Cell-cell signaling: NTF-dependent interactions ...................................26 1.4.2.2 Cell-cell signaling: activity- and neurotransmitter-receptor dependent interactions ..............................................................................................27 1.4.2.3 Cell-cell signaling: ‘black-box’ factors – presynaptic transmitter specificity ................................................................................................29 1.5 Specific
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