After isolating the Sca1+CD45- cardiac population, we added formaldehyde directly to the cell suspension (final concentration 1%) and incubated cells on a shaking platform (10 min, RT). Crosslinking was terminated by adding glycine (0.125 M; 5 min). Crosslinked cells were washed twice with cold PBS and lysed at a density of 5 × 106 cells ml−1 in 1% SDS, 50 mM Tris-HCl (pH 8.0) and 10 mM EDTA, with protease inhibitors (15 min, 4°C). Lysates were sonicated lysates to obtain chromatin fragments <1 kb, then centrifuged (15 min, RT), lysate diluted 1:10 with 1.1% Triton-X100, 2 mM EDTA, 150 mM NaCl and 20 mM Tris-HCl (pH 8.0) containing protease inhibitors, precleared with 50% salmon sperm DNA and protein A agarose slurry (Upstate). Antibodies were added (O/N, 4ºC) (for antibodies used, see Appendix S2). We then added salmon sperm DNA and protein A agarose beads (60 l) and incubated (1 h, 4ºC). Samples were centrifuged and immunoprecipitated pellets washed with 0.1% SDS, 1% Triton-X100, 2 mM EDTA, 20 mM Tris-HCl (pH 8.0), 150 mM NaCl (once); 0.1% SDS, 1% Triton-X100, 2 mM EDTA, 20 mM Tris-HCl (pH 8.0), 500 mM NaCl (once); 0.25 M LiCl, 1% Nonidet P-40, 1% sodium deoxycholate, 1 mM EDTA, 10 mM Tris-HCl (pH 8.0) (once); and 10 mM Tris-HCl (pH 8.0), 1 mM EDTA(twice). Chromatin was eluted from beads twice by incubation with 250 l 1% SDS, 0.1 M NaHCO3 with rotation (15 min, RT). Crosslinking was reversed by adding 20 l 5 M NaCl (4 h, 65°C). Samples were supplemented with 20 l 1 M Tris-HCl (pH 6.5), 10 l 0.5 M EDTA, 20 g RNase A and 40 g proteinase K and incubated (1 h, 45°C), followed by DNA isolation using a kit (MO BIO). Libraries were prepared using the NEBNext Ultra DNA Library Prep for Illumina kit (E7370; New England Biolabs). Briefly, from 1 to 5 ng of input and ChIP-enriched DNA were subjected to end repair and addition of “A” bases to 3′ ends, ligation of adapters and USER excision. All purification steps were performed using AgenCourt AMPure XP beads (A63881, Qiagen). Libraries were amplified by PCR using NEBNext Multiplex Oligos for Illumina (Index Primers Set 1; E7335 or Index Primers Set 2; E7500). Final libraries were analyzed using Agilent High Sensitivity chip to estimate quantity and confirm size distribution, and then quantified by qPCR using the KAPA Library Quantification Kit (KK4835, KapaBiosystems) prior to amplification with Illumina cBot. Libraries were loaded at a 1.42 pM concentration onto the flow cell and were sequenced 1 x 50 on Illumina HiSeq 2500.