Synapse to Nuclear Signaling During Long-Lasting Neuronal Plasticity

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Hebbian and homeostatic forms of synaptic plasticity require new gene expression for their persistence. For stimulus-induced alterations in transcription to occur, signals must be relayed from sites of synaptic stimulation to the nucleus. Such long-distance retrograde transport poses a unique set of challenges in neurons, where synapses can be located at great distances from the cell soma and nucleus. Electrochemical and calcium- dependent processes allow for extremely rapid signaling between subcellular compartments in neurons. Studies in a number of systems have also indicated that soluble signaling molecules can be transported from the synapse to the nucleus to effect changes in transcription. This proposal is aimed at elucidating the cell biology of synapse to nuclear signaling during long-lasting, learning-related synaptic plasticity in mouse hippocampal neurons. During the past funding cycle, we characterized a role for importin-mediated active nuclear import of synaptically localized transcription during hippocampal long-term potentiation. Synapse to nuclear transport of transcription factors provides a direct means of coupling synaptic activity with changes in gene expression. We focus this continuation proposal on the synapse to nuclear transport of the CREB regulated transcriptional coactivator CRTC1 during activity-dependent plasticity. We have shown that CRTC1 tracks glutamatergic activity in excitatory neurons to inform the nucleus about synaptic events. It is actively transported into the nucleus from stimulated synapses, and undergoes profound changes in post-translational modification in response to stimulation. Moreover, while glutamatergic stimuli trigger CRTC1 nuclear import, neuromodulatory inputs that elevate intracellular cAMP regulate the persistence of CRTC1 in the nucleus. We have generated a number of reagents to study and manipulate CRTC1 in neurons and now propose to use these to perform an in-depth analysis of the cell biology and function of its synapse to nuclear signaling during long-term synaptic plasticity of mouse hippocampal neurons. Towards this end we propose three specific aims directed at answering three sets of questions: 1) How does CRTC1 travel from synapse to nucleus; 2) How does CRTC1 nuclear import alter gene expression? How do stimulus-induced change in CRTC1 phosphorylation alter its nuclear transport and downstream transcription? and 3) How does neuromodulation regulate CRTC1-mediated gene expression? The answers to these questions will provide insight into the cell biology of learning-related gene expression, and into the particular function of CRTC1. The results of our studies are relevant to a spectrum of neuropsychiatric disorders, and to cognitive disorders (such as mental retardation, Alzheimer's Disease and age-related memory loss) in which long-term memory is impaired.