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

Takahiko Akematsu,Ronald E Pearlman,Jyoti Garg,Josef Loidl,Jeffrey S Fillingham,Yasuhiro Fukuda

doi:10.7554/elife.26176

Takahiko Akematsu, Ronald E Pearlman + Show 4 more

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https://doi.org/10.7554/elife.26176

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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.

Highlights

DNA double-strand breaks (DSBs) represent one of the greatest threats to genome integrity
We investigate the functions of Tetrahymena TOP2b and SPO11 orthologs in haploid MICs after completing meiosis and show their involvement in Post-meiotic DSBs (PM-DSBs) formation
Self-inflicted DSBs are essential for a wide range of processes, such as TOP2-dependent DNA disentangling (Champoux, 2001), V(D)J recombination (Stavnezer et al, 2008), chromatin diminution (Wang and Davis, 2014), Saccharomyces cerevisiae mating-type switching (Haber, 2012), antigenic variation in Trypanosoma (McCulloch et al, 2015), and, most prominently, meiosis (Keeney et al, 1997)

Summary

Introduction

DNA double-strand breaks (DSBs) represent one of the greatest threats to genome integrity. Markers of DNA lesions such as phosphorylated histone H2AX (gH2AX) foci and terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL)-positive signals are found in the nuclei of elongating spermatids (Marcon and Boissonneault, 2004; Meyer-Ficca et al, 2005; Leduc et al, 2008). Both poly ADP-ribose (PAR) formation, a known DNA damage response (Meyer-Ficca et al, 2005) and DNA polymerase activity, characteristic of DNA repair synthesis, have been detected in these cells (Leduc et al, 2008).

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