Homeotic DUX4 Genes Shape Dynamic Inter-Chromosomal Contacts with Nucleoli in Human Cells.

Nucleoli form interchromosomal contacts with genes controlling differentiation and carcinogenesis. DUX4 genes specify transcription factor possessing two homeodomains. Previously, using Circular Chromosome Conformation Capture (4С) approach on population of cells, it was demonstrated that DUX4 gene clusters form frequent contacts with nucleoli. It was found also that these contacts are almost completely abolished after heat shock treatment. 4C approach as all ligation-mediated methods is capable to detect rather close interactions between chromatin loops in nuclei. In order to independently confirm the formation and the frequency of the contacts in single cells we used FISH approach. Here, we show that DUX genes in single cells form stable contacts in all tested HEK293T cells. During heat shock, DUX4 genes reversibly move 1-3 µm away from the nuclei. We conclude that interchromosomal contacts formed by nucleoli are strong, dynamic, and reversible, providing both the initiation and maintenance of a differentiated state.