Dynamics of Synaptic Proteins in C.elegans

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Long-term visualization of synaptic proteins and spine morphology in mammalian neurons revealed continual turnover of a fraction of synapse population in vitro and in vivo. Furthermore, recent analysis of mammalian synaptic proteins showed rapid alterations of protein compositions in synapses and their regulation by neuronal activity. Significance of continual alterations of synaptic structure and molecular compositions should be evaluated in a system where direct correlational analyses between changes of circuit properties and resulting behavioral alterations are possible. In C.elegans, full descriptions of the circuitry of all 302 neurons are available and specific sets of neurons and genes that control the sensory-motor coordination have been identified. Therefore, long-term visualization of synaptic proteins essential in the proper synaptic functions between neurons involved in the sensory-motor coordination would be an ideal model system to test the behavioral significance of syna … More pse remodeling.To this end, we focused on the glutamatergic synapses between polymodal sensory neuron ASH and interneurons of the locomotory control circuit (command neurons) of C.elegans. The glutamatergic transmission at ASH-command neuron synapses is essential for response to nose-touch. To visualize postsynaptic component, we utilized a fusion protein between ionotropic glutamate receptor GLR-1 and green fluorescent protein (GLR-1::GFP) and expressed this reporter gene either by an authentic glr-1 promoter or nmr-1 promoter that support expression of GLR-1 in a subset of interneurons. Images were obtained by a two-photon laser scanning microscope. Transgenic worms expressing GLR-1-GFP under the control of glr-1 promoter showed fluorescent clusters in both the nerve ring and the ventral nerve cord. Time-lapse imaging of short- and long-term remodeling of GLR-1::GFP clusters in the ventral nerve cord revealed both short-term structural stability and development-dependent remodeling. In transgenic worms expressing GLR-1::GFP under the control of nmr-1 promoter, a smaller number of fluorescent clusters were visualized within the nerve ring. Anatomical location and double labeling of ASH neurons with longer-wavelength fluorescent probes suggested that some of the GLR-1::GFP clusters corresponded to the synaptic junctions between ASH and command neurons. Less