How chromosomes are folded, spatially organized and regulated in three dimensions inside the cell nucleus are among the longest standing questions in cell biology. Genome-wide chromosome conformation capture (Hi-C) technique allowed identifying and characterizing spatial chromatin compartments in several mammalian species. Here, we present the first genome-wide analysis of chromatin interactions in chicken embryonic fibroblasts (CEF) and adult erythrocytes. We showed that genome of CEF is partitioned into topologically associated domains (TADs), distributed in accordance with gene density, transcriptional activity and CTCF-binding sites. In contrast to mammals, where all examined somatic cell types display relatively similar spatial organization of genome, chicken erythrocytes strongly differ from fibroblasts, showing pronounced A- and B- compartments, absence of typical TADs and formation of long-range chromatin interactions previously observed on mitotic chromosomes. Comparing mammalian and chicken genome architectures, we provide evidence highlighting evolutionary role of chicken TADs and their significance in genome activity and regulation.

Recent experimental and computational efforts have provided large data sets describing three-dimensional organization of mouse and human genomes and showed the interconnection between the expression profile, epigenetic state, and spatial interactions of loci. These interconnections were utilized to infer the spatial organization of chromatin, including enhancer–promoter contacts, from one-dimensional epigenetic marks. Here, we show that the predictive power of some of these algorithms is overestimated due to peculiar properties of the biological data. We propose an alternative approach, which provides high-quality predictions of chromatin interactions using information on gene expression and CTCF-binding alone. Using multiple metrics, we confirmed that our algorithm could efficiently predict the three-dimensional architecture of both normal and rearranged genomes.

Chromosomes are hierarchically folded within cell nuclei into territories, domains and subdomains, but the functional importance and evolutionary dynamics of these hierarchies are poorly defined. Here, we comprehensively profiled genome organizations of five Anopheles mosquito species and showed how different levels of chromatin architecture influence contacts between genomic loci. Patterns observed on Hi-C maps are associated with known cytological structures, epigenetic profiles, and gene expression levels. At the level of individual loci, we identified specific, extremely longranged looping interactions, conserved for ~100 million years. We showed that the mechanisms underlying these looping contacts differ from previously described Polycomb-dependent interactions and clustering of active chromatin.

Chromosomes are hierarchically folded within cell nuclei into territories, domains and subdomains, but the functional importance and evolutionary dynamics of these hierarchies are poorly defined. Here, we comprehensively profile genome organizations of five Anopheles mosquito species and show how different levels of chromatin architecture influence each other. Patterns observed on Hi-C maps are associated with known cytological structures, epigenetic profiles, and gene expression levels. Evolutionary analysis reveals conservation of chromatin architecture within synteny blocks for tens of millions of years and enrichment of synteny breakpoints in regions with increased genomic insulation. However, in-depth analysis shows a confounding effect of gene density on both insulation and distribution of synteny breakpoints, suggesting limited causal relationship between breakpoints and regions with increased genomic insulation. At the level of individual loci, we identify specific, extremely long-ranged looping interactions, conserved for ~100 million years. We demonstrate that the mechanisms underlying these looping contacts differ from previously described Polycomb-dependent interactions and clustering of active chromatin.