PNAS 108:5632 (2011)
Co-Occupancy by Multiple Cardiac Transcription Factors Identifies Transcriptional Enhancers Active in Heart.
Aibin Hea,b,1, Sek Won Konga,b,c,1, Qing Maa,b, and William T. Pua,b,2
aDepartment of Cardiology and cChildren’s Hospital Informatics Program, Children’s Hospital Boston, Boston, MA 02115; bHarvard Stem Cell Institute,Harvard University, Cambridge, M
Identification of genomic regions that control tissue-specific gene expression is currently problematic. ChIP and high-throughput sequencing (ChIP-seq) of enhancer-associated proteins such as p300 identifies some but not all enhancers active in a tissue. Here we show that co-occupancy of a chromatin region by multiple transcription factors (TFs) identifies a distinct set of enhancers. GATAbinding protein 4 (GATA4), NK2 transcription factor-related, locus5 (NKX2-5), T-box 5 (TBX5), serum response factor (SRF), and myocyte-enhancer factor 2A (MEF2A), here referred to as "cardiacTFs," have been hypothesized to collaborate to direct cardiac gene expression. Using a modified ChIP-seq procedure, we defined chromatin occupancy by these TFs and p300 genome wide and provided unbiased support for this hypothesis. We used this principle to show that co-occupancy of a chromatin region by multiple TFs can be used to identify cardiac enhancers. Of 13 such regions tested in transient transgenic embryos, seven (54%) drove cardiac gene expression. Among these regions were three cardiac-specific enhancers of Gata4, Srf, and swItch/sucrose nonfermentablerelated,matrix-associated, actin-dependent regulator of hromatin,subfamily d, member 3 (Smarcd3), an epigenetic regulator of cardiac gene expression. Multiple cardiac TFs and p300-bound regions were associated with cardiac-enriched genes and with functional annotations related to heart development. Importantly,the large majority (1,375/1,715) of loci bound by multiple cardiac TFs did not overlap loci bound by p300. Our data identify thousands of prospective cardiac regulatory sequences and indicate that multiple TF co-occupancy of a genomic region identifies developmentally relevant enhancers that are largely distinct from p300-associated enhancers.