High-resolution dissection of human cell type-specific enhancers in cis and trans activities

The spatiotemporal specific gene expression is regulated by cell type-specific regulatory elements including enhancers, silencers and insulators etc. The massively parallel reporter assay (MPRA) methods like STARR-seq facilitate the systematic study of DNA sequence intrinsic enhancer activities in a large scale. However, when applied to human cells, it remains challenging to identify and quantify cell type-specific active enhancers in the genome-wide scale with high-resolution, due to the large size of human genome. In this study, we selected the H3K4me1 associated dinucleosome with the linker DNA sequences as candidate enhancer sequences in two different human cell lines and performed ChIP-STARR-seq to quantify the cell type-specific enhancer activities with high-resolution in a genome-wide scale. Furthermore, we investigated how the activity landscape of enhancer repository would change when transferred from native cells (cis activity) to another cell lines (trans activity). Using ChIP-STARR-seq of the candidate enhancers in native cells and another type of cells, we obtained enhancers cis activity maps and trans activity maps in two different cell lines. The cis and trans activity maps enabled us to identify cell type-specific active enhancers, with enrichment of motifs of differentially expressed TFs. Comparisons between the cis and trans activity maps revealed general consistent regulatory property with different levels of activity in the two cell types, suggesting the sequence intrinsic regulatory properties keep similar in different type of cells. This study provides a new perspective of sequence intrinsic enhancer activities in different types of cells. Overall design: To investigate the genome-wide cis activity and trans activity in high-resolution, we performed ChIP-STARR-seq in two different human cell lines K562 and A549, by isolating the H3K4me1 associated DNA as candidate enhancers in each cell type, transfected the two sets of candidate enhancer sequences to their native cell type and cross-transfected each set to the other type of cell.