TitleInsulator elements mediate long-range interactions between Polycomb targets and between active enhancers in Drosophila
NameLI, Huabing (author), Pirrotta, Vincenzo (chair), Gartenberg, Marc (internal member), Kusch, Thomas (internal member), Chen, J. Don (outside member), Rutgers University, Graduate School - New Brunswick,
DescriptionThe genomic binding sites of Polycomb (PcG) complexes have been found to cluster, forming Polycomb “bodies” or foci in mammalian or fly nuclei. These associations are thought to be driven by interaction between PcG complexes and result in enhanced repression. Similar mechanisms were proposed to explain the clustered genes which share the same transcriptional loci, called “transcription factories”. However, the elements that mediate the long-range interactions and form those bodies remain elusive. The insulator element is a new class of DNA elements and indicated to function in the nuclear structure. Fab-7 and Mcp, the boundaries of cis-regulatory domains of the Bithorax Complex in Drosophila Genome, each contain two functional parts: the silencer (Polycomb Response Element, PRE) and the insulator. Using in-vivo fluorescence imaging and 3C methods, we show that the interactions between remote copies of Mcp or Fab-7 elements are dependent on the insulator activities present in these elements and not on their PREs. However, the interaction ratio is around 6~7%, much lower than the published 20% or 90% interactions. By constructing new transgenic flies, that with enhancer and Mcp flanked by removable lox and frt elements, we have observed high interaction ratio (60~90%) in the Drosophila third instar larva eye discs, low interaction ratio (10~20%) with enhancer deleted, and no interaction (<1%) without Mcp, demonstrating that enhancer is needed for the high stable trans-interactions. We also show that this high interaction is dependent on the insulator protein dCTCF, Mcp PRE part and the Trithorax protein. In addition, a different enhancer could also promote the co-localization. In the related works we conclude that the insulators mediate long-range interactions of PcG targets to form the PcG bodies in the nucleus, and that the insulators also enhance the transcription of active genes by bringing enhancers into the transcription factories. We clarified the mechanism of PcG bodies, and for the first time prove that insulators also mediate long-range interactions between enhancers and bring active transcription units into the transcription factories. In summary, insulators help both silencers and enhancers to build the higher-order organization in the nucleus to regulate gene expression.
NoteIncludes bibliographical references
Noteby Huabing Li
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.