Genetic analysis of cell cycle and chromatin regulation in quiescent fission yeast cells

Abstract: During proliferation, cells produce their genetic materials to increase the number of cells, while in the absence of nutrients or by the induction of stimulus, the proliferative phase is stopped and entry into quiescence is triggered to increase their chance of survival. Quiescence is a reversible resting phase where cells enter, in case of nutrient deprivation or damage and induced by stimuli. In cancer development, the shift between proliferation and quiescence stage is critical since, for example, tumor cells in dormancy are more resistant to cancer treatments. In the resting phase, energy sources are saved by minimizing or stopping the metabolism and cell division in order to use energy for maintaining cell survival. In this case, cells adapt to the new conditions by gene expression reprogramming, which is mediated by chromatin remodeling mechanisms. Therefore, there is a need to investigate mechanisms to understand genes and pathways affecting quiescence entry and maintenance. To investigate the role of genes in quiescence, using high-throughput flow cytometry analysis, we developed the projects to discover new genes and pathways involved in the vegetative or quiescence stages. To achieve this end, we utilized the fission yeast and Schizosaccharomyces pombe which is a convenient model to study both vegetative and quiescence stages. Then, we performed both DNA content and cell survival analysis on the haploid deletion mutant library. Through these original approaches, gene-deleted mutants were classified according to their phenotypes to disclose mechanisms involved in vegetative and quiescence stages. In the present study, different remodeler complexes such as INO80 C, SWR1 C, and SAGA C were investigated and the effect of these complexes on quiescence entry or maintenance was observed. The results demonstrate the effect of remodeler complexes for reprogramming gene expression patterns, that lead cells to enter quiescence or viability of cells during quiescence. The most interesting complex mainly observed was Ino80. Ino80 ATPase-dependent remodeling complex mediates chromatin remodeling by removing histone variant H2A.Z from chromatin. This remodeler complex is required for the regulation of quiescence-related genes. More remodeler complexes and effective genes, that are related to quiescence entry and maintenance, are explained more in details in the result and discussion section.