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

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.DOI: http://dx.doi.org/10.7554/eLife.26176.001

GCNA Interacts with Spartan and Topoisomerase II to Regulate Genome Stability

“…Sperm heads in which chromatin hypercondensation has been disturbed are dramatically misshapen (Gou et al, 2017;Yuen et al, 2014). Topoisomerases, including Top2 and Spo11, create the double strand DNA breaks that facilitate this dramatic germ-cell specific chromatin compaction (Akematsu et al, 2017;Leduc et al, 2008;Marcon and Boissonneault, 2004;Rathke et al, 2007). Top1 may also play a role, as DPCs produced by Top1 poisons induce sperm head abnormalities (R.S et al, 2016).…”

“…Top2 is abundant throughout the germline where it has several germline specific functions including separation of recombined chromosomes, crossover interference, histone exchange, and sperm chromatin condensation (Akematsu et al, 2017;Benkert et al, 2011;Hartsuiker et al, 1998;Hughes and Hawley, 2014;Jaramillo-Lambert et al, 2016;Leduc et al, 2008;Marchetti et al, 2001;Marcon and Boissonneault, 2004;Mengoli et al, 2014;Rathke et al, 2007;Tateno and Kamiguchi, 2001). In accordance with these critical functions, topoisomerase dysfunction during meiosis in a wide array of organisms including yeasts, mammals, fly, and worm causes chromosome segregation defects that result in aneuploidy and chromosome breakage in spores and gametes (Benkert et al, 2011;Hartsuiker et al, 1998;Hughes and Hawley, 2014;Jaramillo-Lambert et al, 2016;Marchetti et al, 2001;Mengoli et al, 2014;Tateno and Kamiguchi, 2001).…”

“…In addition to Top2, germ cells also express a specialized topoisomerase, Spo11. Spo11 is responsible for programmed meiotic double strand breaks and sperm chromatin condensation (Akematsu et al, 2017;Keeney et al, 1997). Taken together, early embryo and germline genomes are expected to carry an extra burden of Topoisomerase DPCs relative to cycling somatic cells.…”

Two different pathways for initiation ofTrichoderma reeseiRad51-only meiotic recombination

“…Top2 has the capability to make DSBs. Top2-dependent post-meiotic DSBs in Tetrahymena thermophila occur in conjunction with the transition from a heterochromatic to euchromatic chromatin structure in the haploid pronucleus [54]. In budding yeast, inactivation of the DNA damage checkpoint kinase Mec1, a homolog of mammalian ataxia telangiectasia and Rad3-related (ATR) protein kinase, leads to Top2-dependent DSBs at fragile sites (referred to as replication slow zones, RSZs).…”

GCNA interacts with Spartan and Topoisomerase II to regulate genome stability

“…Sperm heads in which chromatin hypercondensation has been disturbed are dramatically misshapen (Gou et al, 2017;Yuen et al, 2014). Topoisomerases, including Top2 and Spo11, create the double strand DNA breaks that facilitate this dramatic germ-cell specific chromatin compaction (Akematsu et al, 2017;Leduc et al, 2008;Marcon and Boissonneault, 2004;Rathke et al, 2007). Top1 may also play a role, as DPCs produced by Top1 poisons induce sperm head abnormalities (R.S et al, 2016).…”