RE_LOCATE · Location, location, location: the (re-)positioning of regulatory elements in the mammalian genome.

In mammalian genomes, the enhancers (E) that control a promoter (P) are often scattered over tens to hundreds of kb, and frequently interdigitate with Es that control other nearby Ps. How such apparently haphazard linear arrangements can result in specific gene regulation is a major puzzle. Three main constraints are thought to be involved. First, biochemical compatibility of Es and Ps may ensure that not all Ps respond equally strongly to a given E. Second, chromatin loops may either facilitate or curb particular E-P interactions. Third, Es and Ps are controlled by the local landscape of chromatin modifications. Much is still to be learned about these constraints and their interplay. To unravel the logic of this linear arrangement of Ps and Es, it is necessary to systematically alter the positions of Es, Ps, and elements that control looping. So far, no efficient method has been available for this purpose. We propose to develop and apply RElocate, a scalable, broadly applicable technology to transplant selected DNA elements to hundreds of alternative positions within a ~2 Mb region, and track the functional consequences. We will employ RElocate in combination with a high-throughput combinatorial reporter assay to systematically study how biochemical compatibility may dictate how Es ""choose"" and activate the correct target P(s). Furthermore, we will adapt RElocate to precisely map how loop extrusion shapes E-P interactions, by insertion of hundreds of unidirectional road blocks throughout a locus. Finally, we will use the method to fine-map the repressive/activating chromatin landscape of selected regions at high resolution, and elucidate how Es and Ps may respond differently when inserted throughout this landscape. This work will reveal how the ordering and spacing of regulatory elements along the genome contributes to optimal gene regulation, and will yield a powerful perturbation tool with many applications in genome biology and human genetics.""