Synaptic optogenetics for memory structures

[Speaker] Haruo Kasai:1,2
[Co-author] Makiko Negishi:1,2
1:Graduate School of Medicine, The University of Tokyo, Laboratory of Structural Physiology, Japan, 2:International Research Center for Neurointelligence (WPI-IRCN), UTIAS, The University of Tokyo, Japan

We have developed "synaptic optogenetic probes," such as AS-probes (Hayashi-Takagi et al., Nature 525, 2015), with which we can label enlarged spines after a learning task, and induce shrinkage of these spines to test their role in the learning. We think the probe labels enlarged spines in the following mechanisms. 1) Neuronal activity facilitates transcription of the probe DNA. 2) 3'UTR of the probe promotes transport of mRNA to the dendrite leaving little mRNA in the soma to suppress somatic translation of the probe. 3) Synaptic activity induces efficient translation of the probe around the activated and tagged synapses in dendrites. 4) Enlargement of spines efficiently captures newly synthesized probes. 5) Due to the PEST sequence of the probe, ubiquitin proteasomes degradate excess proteins to prevent labeling of non-stimulated spines. 6) Repetitive and selective activation of the synapses maintains the labeling over one day, suggesting the presence of a discrete learning circuit for each task. We are now improving the promoter, 3'UTR, photoactive peptide, and spine targeting signal to allow visualization of the learning circuits over various brain areas, including the nucleus accumbens, medial prefrontal, and posterior parietal cortices. During improvement of our probes, we found that axonal boutons opposing to the enlarged spines tended to display similar discrete labeling patterns when we chose proper targeting signal and 3'UTR for axonal boutons. We are now confirming the properties of these spine and axonal probes which help us to identify learning circuits at both regional and synaptic levels.

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