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Investigating the roles of cell adhesion molecules in synapse formation and function

Burton, Shawn Denver (2011) Investigating the roles of cell adhesion molecules in synapse formation and function. Master's Thesis, University of Pittsburgh.

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    Abstract

    Recent findings have revealed a crucial contribution of the adhesion molecule neuroligin-1 to the precise organization and regulation of intercellular synaptic connections within the central nervous system, and disruption of neuroligin-1 signaling in vivo fosters cognitive abnormalities. Despite considerable recent progress, several uncertainties remain regarding the exact synaptic function of neuroligin-1. Principle among these uncertainties is whether neuroligin-1 primarily promotes initiation of de novo synaptic connections or maturation of functional, pre-existent connections. To begin to address this, experiments must be devised that are capable of dissociating activity-dependent and -independent effects of neuroligin-1 signaling on pre- and postsynaptic compartments. An additional uncertainty is how and when synapses containing neuroligin-1 are specified as either excitatory or inhibitory. Elucidating these synapse specification cascades will prove crucial in defining the contribution of neuroligin-1 to overall network balances of excitation and inhibition that guide proper cognitive development. A final uncertainty is how alternate adhesion complexes may coordinate with neuroligin-1 to initiate or maintain synaptic connections. Differentiating redundant from complementary functions among adhesion systems will help reconcile unresolved discrepancies between in vitro and in vivo experiments and ultimately provide a clearer understanding of synapse formation and function in vivo. Herein I detail significant new findings clarifying each of these uncertainties. Utilizing a specific transfection protocol, I first demonstrate that neuroligin-1 is capable of robustly inducing presynaptic differentiation independent of proper postsynaptic development and synaptic activity. Second, employing both multi-molecular perturbations and a delimited biological model of the synapse, I show that the postsynaptic scaffolding molecule PSD95 specifically acts downstream of neuroligin-1-mediated synapse initiation. Third, the model synapse is again employed to differentiate between separate synaptic functions of neuroligin-1 and alternate adhesion molecule SynCAM1. Building from these distinct synaptic functions, I provide preliminary evidence that SynCAM1 matures inactive neuroligin-1-initiated synapses. Fourth, I present the first direct evidence that neuroligin-1 contributes to dendritic morphogenesis in mammalian neurons, consistent with recent findings within the Xenopus system. Collectively, these results evince a robust capacity of neuroligin-1 in initial stages of synaptogenesis and contribute to a new theory of neuroligin-1 function in both activity-dependent synapse initiation and activity-dependent synapse maturation.


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    Item Type: University of Pittsburgh ETD
    ETD Committee:
    ETD Committee TypeCommittee MemberEmailORCID
    Committee ChairZeringue, Henry Chcz1@pitt.edu
    Committee MemberJohnson, Jon Wjjohnson@pitt.edu
    Committee MemberMeriney, Stephen Dmeriney@pitt.edu
    Committee MemberCui, X Tracyxic11@pitt.edu
    Title: Investigating the roles of cell adhesion molecules in synapse formation and function
    Status: Unpublished
    Abstract: Recent findings have revealed a crucial contribution of the adhesion molecule neuroligin-1 to the precise organization and regulation of intercellular synaptic connections within the central nervous system, and disruption of neuroligin-1 signaling in vivo fosters cognitive abnormalities. Despite considerable recent progress, several uncertainties remain regarding the exact synaptic function of neuroligin-1. Principle among these uncertainties is whether neuroligin-1 primarily promotes initiation of de novo synaptic connections or maturation of functional, pre-existent connections. To begin to address this, experiments must be devised that are capable of dissociating activity-dependent and -independent effects of neuroligin-1 signaling on pre- and postsynaptic compartments. An additional uncertainty is how and when synapses containing neuroligin-1 are specified as either excitatory or inhibitory. Elucidating these synapse specification cascades will prove crucial in defining the contribution of neuroligin-1 to overall network balances of excitation and inhibition that guide proper cognitive development. A final uncertainty is how alternate adhesion complexes may coordinate with neuroligin-1 to initiate or maintain synaptic connections. Differentiating redundant from complementary functions among adhesion systems will help reconcile unresolved discrepancies between in vitro and in vivo experiments and ultimately provide a clearer understanding of synapse formation and function in vivo. Herein I detail significant new findings clarifying each of these uncertainties. Utilizing a specific transfection protocol, I first demonstrate that neuroligin-1 is capable of robustly inducing presynaptic differentiation independent of proper postsynaptic development and synaptic activity. Second, employing both multi-molecular perturbations and a delimited biological model of the synapse, I show that the postsynaptic scaffolding molecule PSD95 specifically acts downstream of neuroligin-1-mediated synapse initiation. Third, the model synapse is again employed to differentiate between separate synaptic functions of neuroligin-1 and alternate adhesion molecule SynCAM1. Building from these distinct synaptic functions, I provide preliminary evidence that SynCAM1 matures inactive neuroligin-1-initiated synapses. Fourth, I present the first direct evidence that neuroligin-1 contributes to dendritic morphogenesis in mammalian neurons, consistent with recent findings within the Xenopus system. Collectively, these results evince a robust capacity of neuroligin-1 in initial stages of synaptogenesis and contribute to a new theory of neuroligin-1 function in both activity-dependent synapse initiation and activity-dependent synapse maturation.
    Date: 24 June 2011
    Date Type: Completion
    Defense Date: 30 March 2011
    Approval Date: 24 June 2011
    Submission Date: 03 April 2011
    Access Restriction: No restriction; The work is available for access worldwide immediately.
    Patent pending: No
    Institution: University of Pittsburgh
    Thesis Type: Master's Thesis
    Refereed: Yes
    Degree: MSBeng - Master of Science in Bioengineering
    URN: etd-04032011-120246
    Uncontrolled Keywords: adhesion molecules; hippocampal neuron; mixed-culture assay; neuroligin; PSD-95; synapse; synaptogenesis; SynCAM
    Schools and Programs: Swanson School of Engineering > Bioengineering
    Date Deposited: 10 Nov 2011 14:34
    Last Modified: 13 Apr 2012 12:30
    Other ID: http://etd.library.pitt.edu/ETD/available/etd-04032011-120246/, etd-04032011-120246

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