Repair characteristics and time-dependent effects in Saccharomyces cerevisiae cells after X-ray irradiation.

In this study, we examined the dynamics of phenotypic and transcriptional profiles in Saccharomyces cerevisiae following semi-lethal X-ray irradiation. Post-irradiation, reproductive death was revealed as the predominant form of death in S. cerevisiae and almost all the irradiated cells were physically present and intact. In addition, cell cycle arrest reached its peak and cell division was at its valley at 2 h. Cell cycle arrest, cell division potential, DNA damage, and mitochondrial transmembrane potential (MTP) showed significant recovery at 4 h (P > 0.05 vs. control). The improvements of DNA damage and MTP decrease were evaluated as at least 77% and 84% for the original irradiated cells at 4 h, respectively. In the transcriptional profile, the amount of differentially expressed genes (DEGs) and the fold change in the repair-related DEGs were highest at 1 h post-irradiation and then decreased. The DEGs at 1 h (but not 2 h or 3 h) were significantly enriched in gene ontology (GO) categories of detoxification (up) and antioxidant activity (up). Although the transcriptional profile supported the repair time frame observed in the phenotypic profile, the complete repair may take a longer duration as the transcriptional levels of several important repair-related DEGs did not show a decrease and the DNA repair-related pathways (up) were the major enriched pathway in Kyoto Encyclopaedia of Genes and Genomes pathway analysis throughout the whole course of the study. These results provide an important reference for the selection of key time points in further studies.