The Nucleosome Map of the Mammalian Liver

Mammalian genomes contain billions of basepairs of DNA that must be highly compacted as chromatin to fit into the nano-scale of the nucleus, but yet be accessible to allow for transcription to occur. Binding to nucleosomal DNA is critical for ‘pioneer’ transcription factors such as the winged helix transcription factors Foxa1 and Foxa2 to regulate chromatin structure and gene activation. Here we report the genome-wide map of nucleosome positions in the mouse liver, with emphasis on transcriptional start sites, CpG islands, Foxa2 binding sites, and their correlation with gene expression. Despite the heterogeneity of liver tissue, we could clearly discern the nucleosome pattern of the predominant liver cell, the hepatocyte. By analyzing nucleosome occupancy and the distributions of heterochromatin protein 1 (Hp1), CBP (also known as Crebbp), and p300 (Ep300) in Foxa1/2-deficient livers we find, surprisingly, that the maintenance of nucleosome position and chromatin structure surrounding Foxa2 binding sites is independent of Foxa1/2.