Post-meiotic DNA double-strand breaks occur in Tetrahymena, and require Topoisomerase II and Spo11

Elife. 2017 Jun 16;6:e26176. doi: 10.7554/eLife.26176.

Abstract

Based on observations of markers for DNA lesions, such as phosphorylated histone H2AX (γH2AX) and open DNA ends, it has been suggested that post-meiotic DNA double-strand breaks (PM-DSBs) enable chromatin remodeling during animal spermiogenesis. However, the existence of PM-DSBs is unconfirmed, and the mechanism responsible for their formation is unclear. Here, we report the first direct observation of programmed PM-DSBs via the electrophoretic separation of DSB-generated DNA fragments in the ciliate Tetrahymena thermophila. These PM-DSBs are accompanied by switching from a heterochromatic to euchromatic chromatin structure in the haploid pronucleus. Both a topoisomerase II paralog with exclusive pronuclear expression and Spo11 are prerequisites for PM-DSB induction. Reduced PM-DSB induction blocks euchromatin formation, characterized by histone H3K56 acetylation, leading to a failure in gametic nuclei production. We propose that PM-DSBs are responsible for histone replacement during the reprogramming of generative to undifferentiated progeny nuclei.

Keywords: Chromatin remodeling; DNA repair; cell biology; chromosomes; genes; tetrahymena thermophila.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chromatin / metabolism
  • DNA Breaks, Double-Stranded*
  • DNA Topoisomerases, Type II / metabolism*
  • DNA, Protozoan / metabolism*
  • Endodeoxyribonucleases / metabolism*
  • Meiosis*
  • Tetrahymena thermophila / enzymology
  • Tetrahymena thermophila / physiology*

Substances

  • Chromatin
  • DNA, Protozoan
  • Endodeoxyribonucleases
  • meiotic recombination protein SPO11
  • DNA Topoisomerases, Type II