Using epigenome editing of transcriptional enhancers to regulate adult visual cortical plasticity

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Project Summary The synaptic wiring diagram of the cerebral cortex is established during development, and the stability of this network in the adult brain is important for the ability of the cortex to reliably encode information about the sensory world. However, plasticity is also a fundamental feature of the mammalian brain, and a growing body of evidence is revealing that even core features of neuronal response properties, such as the orientation tuning of neurons in the visual cortex, are more dynamically plastic in the adult brain than previously thought. These data raise the question, how is the balance between the stability and the plasticity of synaptic connections maintained in the adult brain? Neuronal activity-dependent transcription and translation play essential roles in the organization of cortical networks during development, and these processes contribute to long-lasting plasticity of neuronal structure and function in the adult brain. Arc is among the most important of the activity regulated genes during cortical development, because Arc protein functions directly at synapses to endocytose AMPA-type glutamate receptors, inducing long-term depression (LTD) and input-specific synaptic elimination. Genetic knockout of Arc in adult primary visual cortex impairs receptive field plasticity, whereas overexpression of Arc enhances this plasticity. These data raise the interesting possibility that the molecular mechanisms of activity-dependent Arc expression may act to set the balance between flexibility and stability of cortical representations. However, no prior study has had the experimental means to selectively manipulate the activity-dependent regulation of genes like Arc in the adult brain in order to determine the consequences for cortical plasticity. The activity-dependent transcription of Arc is mediated by the interaction of the Arc promoter with a distal enhancer element located ~7kB upstream of Arc. We have shown that the CRISPR-based recruitment of dCas9-chromatin regulator fusion proteins to activity-dependent gene regulatory elements can be used to selectively modulate the activity-dependent component of gene expression. Here in Aim 1 we will use two novel strains of dCas9/CRISPR mice we have characterized to titrate the activity-dependent transcription of Arc and determine the consequences for the light-dependent regulation of Arc protein expression in the primary visual cortex (V1) in vivo. In Aim 2 we will use chronic in vivo calcium imaging methods to assess the consequences of impairing Arc induction on the stability and plasticity of orientation tuning in V1. Revealing such a relationship between epigenetic regulation of activity-dependent transcription and synaptic plasticity in the adult visual cortex has the potential to transform how neuroscientists approach the study of cortical function in health and disease.