Polycomb Response Elements


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This is a presentation of a published research paper (not my research) which I created for my Senior seminar in genetics.

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Polycomb Response Elements

  1. 1. Polycomb response elements mediate the formation of chromosome higher-order structures in the bithorax complex Chiara Lanzuolo, Virginie Roure, Job Dekker, Frédéric Bantignies, and Valerio Orlando
  2. 2. Epigenetics <ul><li>Heritable changes in gene expression caused by mechanisms other than changes in the underlying DNA sequence. </li></ul><ul><li>Chromatin remodeling via DNA or histone modification. </li></ul><ul><li>Heterochromatin and euchromatin </li></ul><ul><li>Higher order chromosome structures </li></ul>
  3. 3. Techniques used <ul><li>FISH </li></ul><ul><li>Chromosome Conformation Capture </li></ul><ul><li>RNAi </li></ul>
  4. 4. Terms & Concepts <ul><li>Polycomb Group Genes (PcG): Gene products are proteins that can remodel chromatin such that transcription factors cannot bind to promoter sequences in DNA (repression). PcGs play a role in silencing HOX genes through modulation of chromatin structure (i.e. trans -acting). </li></ul><ul><li>Polycomb Response Elements (PRE): Chromosomal (DNA) regulatory elements that recruit PcG factors to chromatin in vivo (i.e. cis -acting), and mediate epigenetic inheritance of silent and active states throughout development. Located within the Bithorax Complex. </li></ul><ul><li>Bithorax Complex (BX-C): 340kb region which specifies the identities of several posterior abdominal segments; contains 3 Hox genes observed in this paper, each with corresponding PREs. </li></ul><ul><ul><li>HOX Genes: specify the anterior-posterior axis and segment identity during early development of Drosophila and other metazoans. Gene products are transcription factors which must be present in specific gradients throughout the embryo to facilitate proper development. </li></ul></ul>
  5. 5. Hox Gene Mutant
  6. 6. Hox genes & PREs in BX-C <ul><li>Hox Genes: </li></ul><ul><ul><li>abd-A </li></ul></ul><ul><ul><li>abd-B </li></ul></ul><ul><ul><li>Ubx </li></ul></ul><ul><li>PREs </li></ul><ul><ul><li>Fab-7 </li></ul></ul><ul><ul><li>Mcp </li></ul></ul><ul><ul><li>bxd </li></ul></ul><ul><ul><li>Bx </li></ul></ul>
  7. 7. Cell Lines <ul><li>Cultured embryonic cell lines were used </li></ul><ul><li>Schneider 2 (S2): Ubx, abdB, abdA all repressed. </li></ul><ul><li>Schneider 3 (S3): all three abdB transcripts abundant, Ubx and abdA also repressed. </li></ul>
  8. 8. FISH Results
  9. 9. FISH Results
  10. 10. 3C Results
  11. 11. 3C Results-RNAi <ul><li>PcG protein Polycomb ( Pc ) synthesis was reduced via dsRNA in S2 cultures. Transcript was reduced 80% </li></ul><ul><li>After analysis the cell line was allowed to recover Pc activity over ~20 cell divisions. </li></ul>
  12. 12. 3C Results-RNAi
  13. 13. 3C: Distal PREs
  14. 14. Hox Transcripts via rt-PCR
  15. 15. PRE Transcripts via rt-PCR
  16. 16. 3C Results: S3 cells
  17. 17. 3C Results: S3 cells
  18. 18. FISH: S3 cells
  19. 19. Conclusions <ul><li>Silenced BX-C assumes a highly complex topology of the locus that involves all major PcG- regulated DNA elements, including PREs and promoter interactions, as well as long distance PRE-PRE interactions. </li></ul><ul><li>Active BX-C domains lose contact with the core of the repressed structure. </li></ul><ul><li>Forced reactivation of BX-C genes only affects interactions between the AbdB, abdA, and Ubx promoters and the PREs relatively distal from them. The proximal PRE-promoter higher level interaction may lead to successful re-repression when normal amounts of Pc are restored. </li></ul>
  20. 20. Conclusion