High-resolution interrogation of functional elements in the noncoding genome
The noncoding genome plays a major role in gene regulation and disease yet we lack tools for rapid identification and manipulation of noncoding elements. Here, we develop a large-scale CRISPR screen employing ~18,000 sgRNAs targeting >700 kb of noncoding sequence in an unbiased manner surrounding three genes (NF1, NF2, and CUL3) involved in resistance to the BRAF inhibitor vemurafenib in the BRAF-mutant melanoma cell line A375. We identify specific noncoding locations near genes that modulate drug resistance when mutated. These sites have predictive hallmarks of noncoding function, such as physical interaction with gene promoters, evolutionary conservation and tissue-specific chromatin accessibility. At a subset of identified elements at the CUL3 locus, we show that engineered mutations lead to a loss of gene expression associated with changes in transcription factor occupancy and in long-range and local epigenetic environments, implicating these sites in gene regulation and chemotherapeutic resistance. This demonstration of an unbiased mutagenesis screen across large noncoding regions expands the potential of pooled CRISPR screens for fundamental genomic discovery and for elucidating biologically relevant mechanisms of gene regulation.