Genome-Wide Identification of HES1 Target Genes Uncover Novel Roles for HES1 in Pancreatic Development

Notch signalling and the downstream effector HES1 is required for multiple pancreatic cell fate choices during development, but the direct target genes remain poorly characterised. Here we identify direct HES1 target genes on a genome-wide scale using ChIP-seq and RNA-seq analyses combined with human embryonic stem cell (hESC) directed differentiation of CRISPR/Cas9-generated HES1 -/- mutant hESC lines. We found that HES1 binds to a distinct set of endocrine-specific genes, a set of genes encoding basic Helix-Loop-Helix (bHLH) proteins not normally expressed in the pancreas, genes in the Notch pathway, and the known HES1 target NEUROG3. RNA-seq analysis of wild type, HES1 -/- , NEUROG3 -/- , and HES1 -/- NEUROG 3 -/- mutant hESC lines allowed us to uncover NEUROG3-independent, direct HES1 target genes. Among the HES1 bound genes that were derepressed in HES1 -/- NEUROG3 -/- cells compared to NEUROG3 -/- cells, we found members of the endocrine-specific gene set, the Notch pathway genes DLL1 , DLL4 , and HEY1 , as well as the non-pancreatic bHLH genes ASCL1 and ATOH1 . We also found a large number of transcripts specific to the intestinal secretory lineage to be increased in HES1 -/- NEUROG3 -/- cells. Together, our data reveal that HES1 employs a multi-layered control of endocrine differentiation, controls Notch ligand expression independent of NEUROG3, and prevents initiation of ectopic intestinal transcriptional programmes in pancreas progenitors.