Hi-C is a high-throughput genomic and epigenomic technique to capture chromatin conformation (3C).[1] In general, Hi-C is considered as a derivative of a series of chromosome conformation capture technologies, including but not limited to 3C (chromosome conformation capture), 4C (chromosome conformation capture-on-chip/circular chromosome conformation capture), and 5C (chromosome conformation capture carbon copy).[1][2][3][4] Hi-C comprehensively detects genome-wide chromatin interactions in the cell nucleus by combining 3C and next-generation sequencing (NGS) approaches and has been considered as a qualitative leap in C-technology (chromosome conformation capture-based technologies) development and the beginning of 3D genomics.[2][3][4]
Similar to the classic 3C technique, Hi-C measures the frequency (as an average over a cell population) at which two DNA fragments physically associate in 3D space, linking chromosomal structure directly to the genomic sequence.[4] The general procedure of Hi-C involves first crosslinking chromatin material using formaldehyde.[3][4] Then, the chromatin is solubilized and fragmented, and interacting loci are re-ligated together to create a genomic library of chimeric DNA molecules.[4] The relative abundance of these chimeras, or ligation products, is correlated to the probability that the respective chromatin fragments interact in 3D space across the cell population.[4] While 3C focuses on the analysis of a set of predetermined genomic loci to offer “one-versus-some” investigations of the conformation of the chromosome regions of interest, Hi-C enables “all-versus-all” interaction profiling by labeling all fragmented chromatin with a biotinylated nucleotide before ligation.[3][4] As a result, biotin-marked ligation junctions can be purified more efficiently by streptavidin-coated magnetic beads, and chromatin interaction data can be obtained by direct sequencing of the Hi-C library.[3][4]
Analyses of Hi-C data not only reveal the overall genomic structure of mammalian chromosomes, but also offer insights into the biophysical properties of chromatin as well as more specific, long-range contacts between distant genomic elements (e.g. between genes and regulatory elements),[4][5][6] including how these change over time in response to stimuli.[7] In recent years, Hi-C has found its application in a wide variety of biological fields, including cell growth and division, transcription regulation, fate determination, development, autoimmune disease, and genome evolution.[7][5][6] By combining Hi-C data with other datasets such as genome-wide maps of chromatin modifications and gene expression profiles, the functional roles of chromatin conformation in genome regulation and stability can also be delineated.[4]