Large-scale mapping of positional changes of hypoxia-responsive genes upon activation.

Chromosome structure and nuclear organization are important factors in the regulation of gene expression. Transcription of a gene is influenced by local and global chromosome features such as chromatin condensation status. The relationship between the 3D position of a gene in the nucleus and its activity is less clear. Here we used high-throughput imaging to perform a large-scale analysis of the spatial location of nearly 100 hypoxia-responsive genes to determine whether their location and activity state are correlated. Radial distance analysis demonstrated that the majority of Hypoxia-Inducible Factor (HIF)- and CREB-dependent hypoxia-responsive genes are located in the intermediate region of the nucleus, and some of them changed their radial position in hypoxia. Analysis of the relative distances among a subset of HIF target genes revealed that some gene pairs altered their relative location to each other on hypoxic treatment, suggesting higher-order chromatin rearrangements. While these changes in location occurred in response to hypoxic activation of the target genes, they did not correlate with the extent of their activation. These results suggest that induction of the hypoxia-responsive gene expression program is accompanied by spatial alterations of the genome, but that radial and relative gene positions are not directly related to gene activity.