The spinal cord with attached DRG of E12.5 embryos (10 embryos/condition) or isolated DRG of E13.5 (18 embryos/condition) were collected in ice cold PBS and fixed in 1% Formaldehyde in Phosphate Buffer Saline (PBS, pH 7.5) for 15 minutes at room temperature in a shaking plate. The samples were quenched by adding a final concentration of 125 mM Glycine. Library preparation was performed for histone modifications  and transcription factors using TruSeq ChIP library Preparation kit