The sequence of a genome is insufficient to understand all genomic processes carried out in the cell nucleus. To achieve this, the knowledge of its three- dimensional architecture is necessary. Advances in genomic technologies and the development of new analytical methods, such as Chromosome Conformation Capture (3C) and its derivatives, now permit to investigate the spatial organization of genomes. However, inferring structures from raw contact data is a tedious process for shortage of available tools. Here we present TADbit, a computational framework to analyze and model the chromatin fiber in three dimensions. To illustrate the use of TADbit, we automatically modeled 50 genomic domains from the fly genome revealing differential structural features of the previously defined chromatin colors, establishing a link between the conformation of the genome and the local chromatin composition. More generally, TADbit allows to obtain three-dimensional models ready for visualization from 3C-based experiments and to characterize their relation to gene expression and epigenetic states. TADbit is open-source and available for download from http://www.3DGenomes.org.

Structural features of the fly chromatin colors revealed by automatic three-dimensional modeling.