CRISPR Screening Uncovers a Long-Range Enhancer for ONECUT1 in Pancreatic Differentiation and Links a Diabetes Risk Variant [H3K27ac_ChIP-seq]

Functional enhancer annotation is a valuable first step for understanding tissue-specific transcriptional regulation and prioritizing disease-associated non-coding variants for investigation. However, unbiased enhancer discovery in physiologically relevant contexts remains a major challenge. To discover regulatory elements pertinent to diabetes, we conducted a CRISPR interference (CRISPRi) screen in the human pluripotent stem cell (hPSC) pancreatic differentiation system. Among the enhancers uncovered, we focused on a long-range enhancer ~664 kb from the ONECUT1 promoter, as coding mutations in ONECUT1 cause pancreatic hypoplasia and neonatal diabetes. Homozygous enhancer deletion in hESCs was associated with a near-complete loss of ONECUT1 gene expression and compromised pancreatic differentiation. We then identified a type 2 diabetes (T2D) associated variant (rs528350911) in the enhancer which disrupts a GATA motif. Introduction of the risk variant into hESCs revealed substantially reduced binding of key pancreatic transcription factors (GATA4, GATA6 and FOXA2) on the edited allele, accompanied by a subtle reduction of ONECUT1 transcription, supporting a causal role for this risk variant in metabolic disease. This work expands our knowledge about transcriptional regulation in pancreatic development through the characterization of a long-range enhancer and highlights the utility of enhancer discovery in disease-relevant settings for understanding monogenic and complex disease. Chromatin immunoprecipitation DNA-sequencing (ChIP-seq) for H3K27ac in WT and ONECUT1e-664kb deletion hPSC cells (heterozygous and homozygous) differentiated to the pancreatic lineage.