Identification of Hnf6 binding sites in male and female mouse liver

~40,000 HNF6 binding sites were identified in mouse liver chromatin, including several thousand sites showing significant differences in level of HNF6 binding between male and female mouse liver. These sex-biased HNF6 binding sites showed strong enrichment for sex-biased DNase hypersensitive sites and for proximity to genes showing local sex-biased chromatin marks and a corresponding sex-biased expression. ~90% of genome-wide CUX2 binding sites identified previously in female mouse liver (Conforto TL, Zhang Y, Sherman J, Waxman DJ., Mol Cell Biol. 2012;32(22):4611-4627) were also bound by HNF6, giving evidence for genome-wide competition between HNF6 and CUX2 for chromatin binding in female mouse liver. These HNF6/CUX2 common binding sites were enriched for genomic regions more accessible in male than in female mouse liver chromatin, and showed strongest enrichment for male-biased genes, suggesting HNF6 displacement by CUX2 as a mechanism to explain the observed CUX2 repression of male-biased genes in female liver. However, HNF6 binding was sex-independent at a majority of its binding sites, and peak regions of HNF6 binding were frequently associated with co-binding by multiple other liver transcription factors, consistent with HNF6 playing a global regulatory role in both male and female liver. Overall design: Livers were excised from individual male and female mice, cross-linked and sonicated, then used to identify HNF6 binding sites by ChIP-Seq using antibody specific to HNF6 (sc-13050; Santa Cruz Biotechnology, Inc).