CRISPR inhibition of activity-dependent Arc expression in the adult mouse brain has limited effects on plasticity in visual cortex and nucleus accumbens

Neuronal activity drives long-lasting change in circuit function by inducing the expression of gene products that modulate the function of synapses. Arc is one of the most robustly activity-regulated neuronal genes, being induced broadly in neurons by a wide range of physiologically-relevant stimuli. The ability of Arc to promote internalization of AMPA-type glutamate receptors plays an important role in activity-dependent refinement of synaptic connectivity during development. However, the consequences of Arc induction for circuit plasticity in the adult brain are less well understood. We reasoned that we could test the requirement for experience-induced Arc expression in downstream plasticities by disrupting regulatory elements that mediate the inducibility of Arc transcription. To achieve this goal, we developed and validated a CRISPR-based inhibition strategy to conditionally block stimulus-induced expression of Arc in specific regions of the brains of male and female adult mice in vivo. We show that recruiting transgenic dCas9-KRAB to decrease transcriptional activity of either the promoter or the synaptic activity-regulated enhancer of the Arc gene is sufficient to block Arc protein expression in visual cortex (V1) following light exposure or in the nucleus accumbens (NAc) following cocaine administration. However, loss of Arc in V1 failed to alter plasticity of orientation selectivity and loss of Arc in NAc did not block cocaine conditioned place preference or novel object recognition memory. These data show that the relationship between Arc induction and plasticity is not universal and suggest that additional contextual factors determine the functional consequences of Arc induction for plasticity. Significance StatementArc is a neuronal activity-regulated gene whose expression is robustly induced in the adult brain by a wide range of stimuli that drive plasticity. However, the functional requirements of Arc induction for brain plasticity are incompletely understood. Here, we show that we can use transgenic mice expressing the CRISPR-based transcriptional repressor dCas9-KRAB to block stimulus-induced expression of Arc in specific regions of the adult mouse brain. Despite highly effective inhibition of Arc induction, we found that many forms of plasticity remained intact. These data deepen understanding of the contextual importance of activity-induced Arc expression in the adult brain.