The changes of the nuclear landscape upon stimulation of neuronal cells are dependent on the histone deacetylase HDAC1

Spatial chromatin organization is crucial for transcriptional regulation and might therefore be particularly dynamic in neurons since these terminally differentiated cells dramatically change their transcriptome in response to external stimuli. Here, we show that stimulation of neurons causes condensation of large chromatin domains. We find that this phenomenon is not only induced in rat hippocampal neurons cultured in vitro, but is also present in vivo in amygdala neurons of rats subjected to fear conditioning, and hippocampal neurons of animals subjected to kainate evoked seizures or High-Frequency Stimulation (HFS). The activity-induced chromatin condensation is an active, very rapid, and reversible process, that is independent of transcription and precedes the expression of Immediate Early Genes (IEG). It is accompanied by the redistribution of posttranslational modifications of histones, and rearrangements in the spatial organization of chromosome territories. Moreover, it leads to the reorganization of nuclear speckles and active domains located in their proximity. Finally, we find that neurons depleted of the histone deacetylase HDAC1 fail to condense chromatin upon stimulation, a phenomenon that can be fully reversed by the introduction of human HDAC1. Taken together, our results suggest that the HDAC1-dependent chromatin reorganization might constitute an important level of fine-tuning of transcriptional regulation in stimulated neurons. Overall design: Chemically-induced long-term potentiation of synaptic transmission (cLTP) was induced according to previously published protocol (Szepesi et al., 2013) by adding 50?µM forskolin (Sigma Aldrich), 50?nM rolipram (Sigma Aldrich), and 200?µM picrotoxin (Sigma Aldrich) to the medium on DIV13-15. As the chemicals were dissolved in DMSO, the same amount of the solvent was added to the medium of the control.