The histone variant H2A.Z promotes initiation of meiotic recombination in fission yeast

Abstract

Meiotic recombination is initiated by programmed formation of DNA double strand breaks (DSBs), which are mainly formed at recombination hotspots. Meiotic DSBs require multiple proteins including the conserved protein Spo11 and its cofactors, and are influenced by chromatin structure. For example, local chromatin around hotspots directly impacts DSB formation. Moreover, DSB is proposed to occur in a higher-order chromatin architecture termed 'axisloop', in which many loops protrude from cohesin-enriched axis. However, still much remains unknown about how meiotic DSBs are generated in chromatin. Here, we show that the conserved histone H2A variant H2A.Z promotes meiotic DSB formation in fission yeast. Detailed investigation revealed that H2A.Z is neither enriched around hotspots nor axis sites, and that transcript levels of DSB-promoting factors were maintained without H2A.Z. Moreover, H2A.Z appeared to be dispensable for chromatin binding of meiotic cohesin. Instead, in H2A.Z-lacking mutants, multiple proteins involved in DSB formation, such as the fission yeast Spo11 homolog and its regulators, were less associated with chromatin. Remarkably, nuclei were more compact in the absence of H2A.Z. Based on these, we propose that fission yeast H2A.Z promotes meiotic DSB formation partly through modulating chromosome architecture to enhance interaction between DSB-related proteins and cohesin-loaded chromatin.