Briefly, E13 neural progenitor cells were crosslinked with 1% formaldehyde solution (50 mM, HEPES-KOH, pH 7.5, 100 mM NaCl, 1 mM EDTA, 0.5 mM EGTA and 1% formaldehyde) for 10 minutes at room temperature, and the reaction was quenched with glycine. After washing two times with ice-cold PBS, cells were resuspending the cells in lysis buffer 1(50 mM HEPES-KOH, pH 7.5, 140 mM NaCl, 1 mM EDTA, 10% glycerol, 0.5% NP-40, 0.25% Triton X-100, 1x protease inhibitors) for 10 minutes at 4℃. Nuclei were isolated at at 4000rpm for 5 minutes at 4°C and resuspended in lysis buffer 2 (10 mM Tris-HCl, pH 8.0, 200 mM NaCl, 1 mM EDTA, 0.5 mM EGTA, 1x protease inhibitors), and then rocked gently at room temperature for 10 minutes. Nuclei was sonicated in lysis buffer 3 (1% SDS, 10 mM EDTA, 50 mM Tris-HCl pH 8.1, 1x Protease Inhibitor) using a Scientz-IID sonicator. Chromatin was immunoprecipitated overnight at 4℃with 50 μl Protein A bead (Dynabeads, Invitrogen) pre-coupled with 2 μg appropriate antibodies. Beads were washed three times with low-salt buffer (0.1% SDS, 1% Triton X-100, 2 mM EDTA, 150 mM NaCl, Tris-HCl, pH 8.1) and three times with high-salt buffer buffer (0.1% SDS, 1% Triton X-100, 2 mM EDTA, 500 mM NaCl, Tris-HCl, pH 8.1). After reverse crosslinking was performed, DNA was eluted and purified using a DNA purification kit (Tiangen). Libraries were prepared according to Illumina's instructions accompanying the DNA Sample Kit (Part# 0801-0303). Briefly, DNA was end-repaired using a combination of T4 DNA polymerase, E. coli DNA Pol I large fragment (Klenow polymerase) and T4 polynucleotide kinase. The blunt, phosphorylated ends were treated with Klenow fragment (32 to 52 exo minus) and dATP to yield a protruding 3- 'A' base for ligation of Illumina's adapters which have a single 'T' base overhang at the 3’ end. After adapter ligation DNA was PCR amplified with Illumina primers for 15 cycles and library fragments of ~250 bp (insert plus adaptor and PCR primer sequences) were band isolated from an agarose gel. The purified DNA was captured on an Illumina flow cell for cluster generation. Libraries were sequenced on the Genome Analyzer following the manufacturer's protocols.