Technologies for studying 4D nucleome. Technologies for 4D nucleome research are classified into two types: genomics and imaging-based methodologies. 3C-based and ligation-free methods are the major two types of genomics-based tools. Imaging-based tools are further classified into FISH-based methods and live-cell imaging. A main principle and workflow are demonstrated in the figure for each method (written in bold letters). For 3C-based methodologies, modifications of 3C workflow are depicted or described with the corresponding method in colored boxes. The location of method indicates where the modification has been applied in 3C workflow. For example, DNase-Hi-C uses DNase for fragmentation instead of a six or four cutter enzyme, therefore located under ‘Crosslinking’ step, indicating that the modification is applied after the crosslinking step. Downstream applications are represented with the method via color-coded squares: blue square for PCR, green square for microarray and orange square for sequencing. In addition, the scale of each method is shown in different colors of the square background: skin color for population studies and light pink for sing-cell studies.