Molecular Motors in Cargo Trafficking and Synapse Assembly
Every production process, be it cellular or industrial, depends on a constant supply of energy and resources. Synapses, specialized junctions in the central nervous system through which neurons signal to each other, are no exception to this rule. In order
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Molecular Motors in Cargo Trafficking and Synapse Assembly Robert van den Berg and Casper C. Hoogenraad
Abstract Every production process, be it cellular or industrial, depends on a constant supply of energy and resources. Synapses, specialized junctions in the central nervous system through which neurons signal to each other, are no exception to this rule. In order to form new synapses and alter the strength of synaptic transmission, neurons need a regulatory mechanism to deliver and remove synaptic proteins at synaptic sites. Neurons make use of active transport driven by molecular motor proteins to move synaptic cargo over either microtubules (kinesin, dynein) or actin filaments (myosin) to their specific site of action. These mechanisms are crucial for the initial establishment of synaptic specializations during synaptogenesis and for activity-dependent changes in synaptic strength during plasticity. In this chapter, we address the organization of the neuronal cytoskeleton, focus on synaptic cargo transport activities that operate in axons and dendrites, and discuss the spatial and temporal regulation of motor proteinbased transport. Keywords Actin • Axon • Cytoskeleton • Dendrite • Disease • Dynein • Kinesin • Microtubule • Myosin • Neuron • Synapse • Synaptic plasticity
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Introduction
One apparent feature of neurons is that once the axon and dendrites have grown out, they establish synaptic contacts forming neuronal networks that propagate information in a unidirectional fashion. Excitatory synaptic signaling in the brain occurs by releasing glutamate from “sending” neurons and activating glutamate receptors
R. van den Berg • C.C. Hoogenraad (*) Cell Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584CH, Utrecht, The Netherlands e-mail: [email protected] M.R. Kreutz and C. Sala (eds.), Synaptic Plasticity, Advances in Experimental Medicine and Biology 970, DOI 10.1007/978-3-7091-0932-8_8, # Springer-Verlag/Wien 2012
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at “receiving” neurons (Sheng and Hoogenraad 2007; S€udhof 2004). Structurally, synapses are divided into two specialized domains: the presynaptic bouton on the axon side of the “sending neuron” and the postsynaptic compartment on the dendrite of the “receiving” neuron. The directional nature of signal relay requires that synaptic contacts are morphologically asymmetric with distinct protein components. Recent studies have identified the molecular components of synapses, particularly by using genetic and proteomic strategies, and have revealed that the specification of synaptic function, for example, excitatory or inhibitory, at both preand postsynapses is achieved via the recruitment and assembly of very distinct synaptic complexes (Jin and Garner 2008; Kim and Sheng 2004; Margeta et al. 2008; Sheng and Hoogenraad 2007). Proper arrangement of pre- and postsynaptic membranes and organization of pre- and postsynaptic compartments is essential for accurate synaptic signaling, neural network activity, and cognitive processes such
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