DeTOKI identifies and characterizes the dynamics of chromatin topologically associating domains in a single cell

Abstract

The human genome has a dynamic, well-organized hierarchical 3D architecture, including megabase-sized topologically associating domains (TAD). TADs are a key structure of the genome regulating nuclear processes, such as gene expression, DNA replication and damage repair. However, owing to a lack of proper computational tools, TADs have still not been systematically and reliably surveyed in single cells. In the present work, we developed a new algorithm to decode TAD boundaries that keep chromatin interaction insulated (deTOKI) from ultra-sparse Hi-C data. By nonnegative matrix factorization, this novel algorithm seeks out for regions that insulate the genome into blocks with minimal chance of clustering. We found that deTOKI outperformed competing tools and that it reliably identified TADs with single-cell Hi-C (scHi-C) data. By applying deTOKI, we found that domain structures are prevalent in single cells. Further, although domain structures are highly dynamic between cells, TADs adhere to the ensemble, suggesting tight regulation of single-cell TADs. Finally, we found that the insulation properties of TAD boundaries have major effect on the epigenetic landscape in individual cells. In sum, deTOKI serves as a powerful tool for profiling TADs in single cells.