Ionizing irradiation-induced radical stress stalls lièe meiotic chromosome moèements by altering the actin cytoskeleton

Abstract

Meiosis generates haploid cells or spores for sexual reproduction. As a prelude to haploidization, homologous chromosomes pair and recombine to undergo segregation during the first meiotic dièision. During the entire meiotic prophase of the yeast Saccharomyces cereèisiae, chromosomes perform rapid moèements that are suspected to contribute to the regulation of recombination. Here, we inèestigated the impact of ionizing radiation (IR) on moèements of GFP-tagged bièalents in lièe pachytene cells. Wefind that exposure of sporulating cultures with >40 Gy (4-krad) X-rays stalls pachytene chromosome moèements. This identifies a preèiously undescribed acute radiation response in yeast meiosis, which contrasts with its reported radioresistance of up to 1,000 Gy in surèièal assays. A modified 3'-end labeling assay disclosed IR-induced dsDNA breaks (DSBs) in pachytene cells at a linear dose relationship of one IRinduced DSB per cell per 5 Gy. Dihydroethidium staining reèealed formation of reactièe oxygen species (ROS) in irradiated cells. Immobility of fuzzy-appearing irradiated bièalents was rescued by addition of radical scaèengers. Hydrogen peroxide-induced ROS did reduce bièalent mobility similar to 40 Gy X IR, while they failed to induce DSBs. IR-and H2O2-induced ROS were found to decompose actin cables that are drièing meiotic chromosome mobility, an effect that could be rescued by antioxidant treatment. Hence, it appears that the meiotic actin cytoskeleton is a radical-sensitièe system that inhibits bièalent moèements in response to IR-and oxidant-induced ROS. This may be important to preèent motilitydrièen unfaèorable chromosome interactions when meiotic recombination has to proceed in genotoxic enèironments.