Chromatin regulation of neuronal activity-induced enhancer priming and epigenetic memory

Summary: Neuronal activity-induced gene expression is essential for converting transient stimuli into long-term changes in brain function by modulating synaptic activity, neuron morphology, circuit formation, and behavioral adaptation. Neural plasticity relies on the proper induction of activity-regulated genes (ARGs) through activated Ca2+ signaling cascades and downstream transcription factors and chromatin regulators. We demonstrated for the first time that previous stimulation of ARGs can prime the genes, resulting in faster and more robust expression upon subsequent stimulation, possibly due to epigenetic memory. Intriguingly, it has been reported that cocaine induces gene activation and epigenetic priming in the reward circuit in vivo, which could share similar epigenetic mechanisms as in our experimental systems. The key question is how chromatin regulators prime ARG enhancers at a poised state after a transient neuronal stimulation, leading to stronger response to subsequent stimulation even after an extended period. Mammalian SWI/SNF-like chromatin remodeling BAF complexes, containing core ATPase subunits BRG1/SMARCA4, play significant roles in signaling-induced transcription. Mutations in BAF subunits are associated with neurodevelopmental or psychiatric diseases. We have shown that BRG1 regulates ARG induction by controlling both enhancer chromatin environment and E/P looping. Importantly, we identified a serine phosphorylation site in BRG1, induced by various neuronal stimuli through Ca2+ signaling, which is crucial for ARG enhancer activation. Using mice with BRG1 knock-in phospho- mutations, we demonstrated that BRG1 phosphorylation promotes ARG priming. Cohesin mediated 3D genome reprogramming was identified as a potential priming factor regulated by activity-induced BRG1 phosphorylation. Thus, we hypothesize that neuronal activity-induced BRG1 phosphorylation regulates enhancer priming and epigenetic memory through establishing a cohesin-mediated primed state of chromosome 3D structure. We propose three aims to test this hypothesis. We propose three aims to test this hypothesis. (1) Determine how neuronal activity-induced BRG1 phosphorylation regulates enhancer priming through establishing a cohesin- mediated primed state of chromosome 3D structure. (2) Determine the function of cohesin in BRG1 phosphorylation dependent ARG enhancer priming. (3) Examine the function of BRG1 phosphorylation in regulating cocaine-induced gene activation and priming. Our study will provide significant insights into both the epigenetic mechanism of neural plasticity and the molecular functions of chromatin regulators in neural disorders.