Hippocampi were micro-dissected after cervical dislocation, washed in ice-cold PBS and pooled together, when fixation was needed 1% FA was used. Nuclei were isolated using our improved FANS protocol for SUN1-GFP+ cells. Extensive description of protocols indicated in Supplemental Experimental Procedures. ATAC-seq experiments were conducted as the original protocol (Buenrostro et al., 2013), using anti-NeuN (Millipore MAB377) to select mature neurons. Libraries were prepared with TruSeq.