%0 Generic
%A Petretich, Massimo
%D 2016
%F heidok:21976
%R 10.11588/heidok.00021976
%T Importance of Chromosomal Architecture to Organize Promoter-Enhancer Long-Range Interactions in c-Myc locus
%U https://archiv.ub.uni-heidelberg.de/volltextserver/21976/
%X In metazoans the regulation of transcription commonly relies on multiple types of regulatory elements. Often these elements are separated from their target promoters by great genomic distance and can even have other genes in between. Current models propose the chromosomes to be folded following a specific topology in order to allow these long-range interactions to occur. In addition to the locus topology, chromatin environment and DNA accessibility play an important role to determine the activity of regulatory elements.  Thanks to genome-wide studies these layers of regulation have been shown to correlate with gene expression to different extents, however it is still not clear how chromatin, DNA topology and genetic components integrate in order to carry out this process. With this project we aim to understand basic mechanisms organizing promoter–regulatory elements communication in a defined model locus.  A previous project from the laboratory used chromosomal deletions and in vivo reporter assays to identify and characterize regulatory elements in c-Myc locus. This study, performed by Veli Uslu showed that during mouse embryonic development, at 11.5 days of gestation, different enhancers coordinate c-Myc transcription in the facial tissues and embryonic liver. We analyzed the distribution inside c-Myc locus of histone modifications enriched at enhancer sites, restricting to few smaller putative regions the genetic position of facial and liver enhancers. We also assessed the occupancy of the architectural protein CTCF, enriched at sites involved in long- range interactions and on insulators, finding both tissue-invariant and tissue-specific binding sites at different parts of the locus.  To study if the topology of the locus influences enhancer promoter communication and how it does this, we created three lines of mice carrying different chromosomal inversions. Each of which reshuffles the relative positions of the different genetic elements: c-Myc promoter, enhancers and CTCF binding sites.  The observed effects of the genetic engineering include significant reductions of c-Myc expression in the facial tissues and redirection of regulatory activity to other  1  genes. In the liver we saw instead milder and non-significant effects of the inversions on c-Myc regulation.  We investigated the occupancy of CTCF and the Cohesin complex subunit RAD21 (another architectural protein) in the facial mesenchyme and liver, on the engineered lines, detecting in c-Myc locus just some minor changes compared to the Wt.  Our data suggest that the architecture of the loci may have a functional role in organizing promoters-regulatory elements interactions, and, if altered, can lead to genes misexpression. In case architectural proteins are involved in this process, our data suggests that their binding to the genome, not significantly altered by genetic reshuffling, may be mostly determined by the DNA sequence (genetics). On the other hand, it is possible that the long-range interactions engaged by these proteins may be influenced more by their working context.