CD8SP from pooled thymus were isolated and crosslinked with formaldehyde 1% for 10min at room temperature before staining. Crosslinking was stopped with 0.125 M glycine. Cells then were washed twice by ice-cold PBS and sorted. Each sorted cell-population was resuspended with ChIP-lysis buffer (10mM Tris pH8, 140mM NaCl, 1mM EDTA, 1% Triton x-100, 0.5% SDS, 0.1% Na-Deoxycholate) for 10min on ice supplemented with PIC (proteinase inhibitors cocktail) and sheared to have a fragments size range between 200-600bp. After clearance by centrifugation at 4°C, sheared chromatin used for each immunoprecipitation of histone marks or transcription factors. For histones marks, library preparation was performed using TruSeq ChIP library Preparation kit using 3-6ng of ChIPed DNA. For transcription factors, the library preparation was done with MicroPlex Library Preparation kit with 0.5ng od ChIPed DNA