Analysis of FoxA2 occupancy in mouse liver with endoderm ChIP-chip array. Mus musculus

Understanding how silent genes can be competent for activation provides insight into development as well as cellular reprogramming and pathogenesis. We performed genomic location analysis of the pioneer transcription factor FoxA in the adult liver and found that about one-third of the FoxA bound sites are near silent genes, including genes without detectable RNA polymerase II. Virtually all of the FoxA-bound silent sites are within extended conserved sequences, suggesting possible function. Such sequences are enriched in motifs for transcriptional repressors, including for Rfx1. We found one such target site containing functional FoxA and Rfx1 sites is a cryptic enhancer 7 kb downstream of the Cdx2 gene, the latter being an effector of esophageal metaplasia. Indeed, Rfx1 sites restrict transcriptional activation by FoxA at the +7 kb Cdx2 element. Furthermore, Rfx1 expression in the esophageal epithelium becomes extinguished during its metaplastic progression to carcinoma. We propose that motif analysis of other transcription factors bound to silent genes can reveal unanticipated regulatory networks that provide insights into reprogramming and oncogenic progression. Overall design: We analyzed FOXA2 occupancy in a mouse liver sample. We ran three competitive hybridizations: (i) FOXA2 vs IgG, (ii) FOXA2 vs input, and (iii) IgG vs input.