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Genomic Scars Generated by Polymerase Theta Reveal the Versatile Mechanism of Alternative End-Joining

Robin van Schendel1, Jane van Heteren1, Richard Welten1

  • 1Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands.

Plos Genetics
|October 19, 2016
PubMed

Insights

DNA damage can cause large genomic deletions through polymerase Theta (POLQ)-mediated end joining (TMEJ) of double-strand breaks (DSBs). This study reveals the mechanism behind these mutations in model organisms.

Area of Science:

  • Molecular Biology
  • Genetics
  • Genomics

Background:

  • Genotoxic agents are widely used to induce mutations for studying genotype-phenotype relationships.
  • The mechanism by which DNA damage leads to severe genomic alterations beyond single nucleotide variants was previously unknown.

Purpose of the Study:

  • To elucidate the mechanism underlying deletion mutagenesis induced by common genotoxic agents.
  • To investigate the role of polymerase Theta (POLQ)-mediated end joining (TMEJ) in generating deletions.

Main Methods:

  • Utilized ethyl methanesulfonate (EMS) and photo-activated trimethylpsoralen (UV/TMP) as mutagens in model organisms.
  • Analyzed approximately 7,000 deletion alleles in C. elegans, focusing on breakpoints and junctions.
  • Characterized the in vivo mechanism of POLQ action.

Main Results:

  • Demonstrated that deletion mutagenesis results from POLQ-mediated end joining (TMEJ) of double-strand breaks (DSBs).
  • Identified a distinct order of events in TMEJ, involving primer extension using downstream break ends.
  • Showed resolution occurs when 3' overhangs have matching ends.

Conclusions:

  • Established a step-wise model for the in vivo mechanism of POLQ action.
  • Explained the molecular basis of mutagen-induced deletion alleles.
  • Provided insights into an alternative end-joining repair pathway for DNA damage.

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