Genome-wide maps of Foxa2 binding sites in mouse embryonic stem cell-derived definitive endoderm cells

Foxa2 is required for endoderm differentiation into hepatic lineage. The mechanism of activation for Foxa2 during this developmental process has not been elucidated yet. We established an in vitro system to guide ES cells differentiating into definitive endoderm (DE) cells and the following DE cells to early hepatic cells. ChIP-seq assays have been successfully performed to assess Foxa2 binding profile. Over 50% of Foxa2 target genes in DE cells were found being activated in hepatic cells which were at a stage later than DE stage. Therefore, our finding at genome-wide level proved Foxa2 serving as a pioneer factor at DE stage. Furthermore, Foxa2 could specifically induce H3K4me2 modifications to the promoter/enhancer regions of many hepatic genes to pre-mark the chromatin, and determine the hepatic lineage differentiation competence. Our study illustrated the wide existence of Foxa2’s pioneer factor function and uncovered the correlation between pioneer factor and chromatin pre-mark. These findings will be helpful for understanding the developmental process of hepatogenesis and efficiently controlling Foxa2 during hepatic induction for generating functional hepatocytes.