Glutamate receptor recruitment to new synapses in vivo

University Of Oregon, Eugene OR

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Abstract

DESCRIPTION (provided by applicant): Chemical synapses are the primary means for transmitting information from one neuron to the next. Synapses are initially formed during development of the nervous system, and formation of appropriate synapses is crucial for establishment of neuronal circuits that underlie behavior and cognition. Minor irregularities during synapse formation can lead to developmental disorders such as autism, mental retardation and may contribute to psychological disorders. Most synapses in the vertebrate central nervous system (CNS) depend on the neurotransmitter glutamate, and thus glutamatergic synapses have been an important focus of study in trying to unravel these and other neurological disorders. A novel family of cell adhesion molecules (CAMs), the Synaptic Cell Adhesion Molecules (SynCAMs), has recently been proposed to mediate the formation of synapses. However, this work is based on experiments in neuronal culture, and knock-out mouse data so far does not corroborate this. Furthermore, it remains unknown how the SynCAMs, and CAMs in general, bring about the recruitment of synaptic elements to new adhesive contacts. We propose to test a model describing specific mechanisms through which SynCAM family members 1 and 2 can recruit both synaptic vesicles (SVs) to the presynaptic terminal and glutamate receptors to the postsynaptic specialization. We hypothesize that an interaction between SynCAM1 or 2 and CASK in axons can directly tether SV precursors to the site of SynCAM/SynCAM interaction. We also propose that binding of DAL-1 to SynCAM1 or 2 in dendrites results in formation of an actin/spectrin subsynaptic scaffold. These cytoskeletal elements then serve two functions: 1) strengthening of the adhesive nature of the synapse and morphological remodeling to generate a spine and 2) recruitment of NMDA type glutamate receptor transport packets via an actin-dependent transport mechanism. We propose to use a variety of techniques including biochemistry, immunolabeling, live-imaging, electrophysiology and behavioral tests, because a multidisciplinary approach will comprehensively test our model. We also propose to use various neuronal preparations for our experiments including cultured hippocampal neurons, cultured cerebellar granule cells (CGCs) and spinal cord neurons in zebrafish embryos in vivo. Testing our hypothesis in zebrafish will shed light on whether these proteins and their interactions are required for forming a specific circuit in a developing embryo that is required for a sensorimotor reflex. Our approach gives us the unprecedented opportunity to determine the mechanisms of glutamatergic synapse formation using behavioral, electrophysiological, genetic and biochemical approaches in both neuronal cultures and in a living vertebrate.