Genomic context sensitizes regulatory elements to genetic disruption [DNAse-seq]
Enhancer function is frequently investigated piecemeal using truncated reporter assays or single deletion analysis, thus it remains unclear to what extent their function is influenced by surrounding genomic context. Using our Big-IN technology for targeted integration of large DNAs, we analyzed the regulatory architecture of the Igf2/H19 locus, a paradigmatic model of enhancer selectivity. We assembled payloads containing a 157-kb functional Igf2/H19 locus and engineered mutations to genetically direct CTCF occupancy at the imprinting control region (ICR) that switches the target gene of the H19 enhancer cluster. Contrasting the activity of payloads delivered to the endogenous locus or to a safe harbor locus (Hprt) revealed that the functional elements comprising the Igf2/H19 locus are highly sensitive to their native context. Exchanging components of the Igf2/H19 locus with the well-studied Sox2 locus showed that the H19 enhancer cluster in particular functioned poorly out of context, and required its native surroundings to activate Sox2 expression. Conversely, the Sox2 locus control region (LCR) could activate both Igf2 and H19 outside its native context, but its activity was only partially modulated by CTCF occupancy at the ICR. Analysis of regulatory DNA actuation across different cell types revealed that, while the H19 enhancers are tightly coordinated within their native locus, the Sox2 LCR acts more independently. We show that these enhancer clusters typify broader classes of loci genome-wide. Our results show that unexpected dependencies may influence even the most studied functional elements, and our synthetic regulatory genomics approach permits large-scale manipulation of complete loci to investigate how locus architecture relates to function. Overall design: DNase-seq mapping in engineered  mesendodermal cells differentiated from mouse embryonic stem cells (mESCs) using CHIR. Single DNase-seq sample in WT mesendodermal cells used as a reference