Mechanisms of neuron-oligodendrocyte precursor cell interactions

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The myelin sheath is a multilayered membrane generated by specialized glial cells called oligodendrocytes (OLs) that iteratively spiral their plasma membranes around axon segments in the vertebrate central nervous system (CNS). OLs derive from OL precursor cells (OPCs), and functional interactions between neurons and OLs as well as between neurons and OPCs are critical for CNS function and health. A specialized but very poorly understood interaction between neurons and OPCs occurs at the neuron-OPC synapse: nearly all OPCs form synapses postsynaptically to neurons. OPCs differ from mature neurons in many ways: they migrate, frequently remodel processes, and are capable of transforming their processes into myelin sheaths. These unique cellular features raise questions as to whether neuron-OPC synapses adapt to an OPC's unique biology and employ distinct mechanisms for synapse development. Despite previous EM and electrophysiological characterizations, almost nothing is known about synapse development in OPCs, the molecular mechanisms that govern neuron-OPC synapse formation, and how signaling via neuron-OPC synapses influences myelination. Here we propose to use zebrafish to investigate neuron-OPC synapse development, the relationship of these synapses to myelination, and to probe the underlying molecular mechanisms regulating these processes. Zebrafish provide unparalleled optical clarity for in vivo imaging and powerful tools for rapid genetic manipulations. We have identified the presence of two postsynaptic scaffolds, PSD-95 and gephyrin, at neuron-OPC synapses and generated new tools to label synapses containing these scaffolds in OPCs. Our preliminary results suggest unique synapse assembly and disassembly mechanisms in OPCs and highlight potential roles for synapses in OPC development and myelination. In this application, we will determine if and how neuron-OPC synapses are correlated with OPC differentiation and subsequent myelination (Aim 1). We will also employ cell-specific knockdown approaches to identify genes that are critical for synapse development and assess their roles in OPC biology (Aim 2). Together, our work can define previously unknown functions for neuron-OPC synapses and reveal important mechanisms that mediate neuron-glial interactions in the vertebrate CNS.