The second decade of 3C technologies: Detailed insights into nuclear organization

The relevance of three-dimensional (3D) genome organization for transcriptional regulation and thereby for cellular fate at large is nowwidely accepted. Our understanding of the fascinating architecture underlying this function is based on microscopy studies as well as the chromosome conformation capture (3C) methods, which entered the stage at the beginning of the millennium. The first decade of 3C methods rendered unprecedented insights into genome topology. Here, we provide an update of developments and discoveries made over the more recent years. As we discuss, established and newly developed experimental and computational methodsenabled identification of novel, functionally important chromosome structures. Regulatory and architectural chromatin loops throughout thegenomeare being cataloged and compared between cell types, revealing tissue invariant and developmentally dynamic loops. Architectural proteins shaping thegenome were disclosed, and their mode of action is being uncovered. We explain how more detailed insights into the 3D genome increase our understanding of transcriptional regulation in development and misregulation in disease. Finally, to help researchers in choosing the approach best tailored for their specific research question, we explain the differences and commonalities between the various 3C-derived methods.