Cells were isolated by tissue digestion and fluorescence activated cell sorting for viable CD45-Ly51loMHCIIhi as MECs. Chromatin IPed with specific Abs was eluted from the Protein-G beads, treated with 1µg DNase-free RNase (Roche) for 30 min at 37°C and with Proteinase K (Roche) for 2 hrs at 37°C followed by reverse cross-linking by leaving the plate at 65°C overnight. DNA from reverse cross-linked material was purified with SPRI beads (Agencourt AMPure XP beads, Beckman Coulter); and sequential steps of end-repair, A-base addition, adaptor-ligation and PCR amplification (15 cycles) were performed to prepare the ChIP-seq library for each sample.