Induction of post-meiotic DNA double-strand breaks by the Pnu1 endonuclease in  Schizosaccharomyces pombe .
Meiosis is a source of genetic variation in eukaryotes. Meiosis in the eukaryotic fission yeast  Schizosaccharomyces pombe  leads to the formation of spores that are particularly resistant to environmental stresses. In addition to external factors, internal processes may nevertheless contribute to cellular stress and impact the genome. This study investigates the role of Pnu1 as the major meiotic nuclease in  S. pombe . Transcription and cellular expression of Pnu1 are regulated upon specific phases of meiosis while its mitochondrial localization is also altered during this process. As a result, Pnu1 induces fragmentation of both genomic and mitochondrial DNA in the post meiotic phase. This sugar-non-specific endonuclease generates random double-strand breaks across the genome, an activity that appears to be mediated by direct interaction with chromatin. Given the high spore viability (∼95%) and the widespread occurrence of this phenomenon, this fragmentation appears to be physiological rather than apoptotic as observed in mammals. EndoG is the mammalian homolog of Pnu1 and is a caspases-independent apoptotic endonuclease that can allow cell survival. This study further describes the dynamics of Pnu1 action and support the conclusion that Pnu1 is a major meiotic endonuclease of  S. pombe  responsible for a transient post-meiotic fragmentation of cellular DNA potentially contributing to genetic variability.
Mourrain L, Cavé T, Boissonneault G