The Roles Of R-loop In Meiosis Of Saccharomyces Cerevisiae

Meiosis is the essential step of sexual reproduction for eukaryotes.During meiosis,the cell does one round of DNA replication followed by two rounds of chromosome segregation,which will create gametes containing only half of the parental chromosome complements.After that,the gametes combine to form a zygote,making the chromosome number of the child the same as the parents.In this process,the number of chromosomes in the parent-child generation is constant to maintain genetic stability of species.At the same time,homologous recombination and the independent assortment of parental chromosomes can produce new characters differ from parents,which can be thought as the adaption to the environment changes and the important mechanism for evolution.Meiotic defects in human cells can cause many diseases including Down's syndrome,so investigating the mechanism of meiotic division is of great significance for clinical treatment and promoting human health.In meiosis,the prophase of the MI can be divided into five periods,including leptotene,zygotene,pachytene,diplotene,and diakinesis.Homologous recombination is initiated by double-strand break(DSB)during leptotene,which is followed by SEI and dHJ and eventually produce a structure called crossover(CO)in pachytene.CO is essential for accurate homologous chromosome segregation during meiosis MI,so the key events of MI prophase is indeed an important research focus of the entire process of meiosis.R-loop is a co-transcriptionally three-strand structure,which consists of a DNA-RNA hybrid and a single non-template DNA strand.R-loop does severe harm to the genome integrity due to its exposed non-template DNA strand and is of great importance to gene expression and regulation because of its impediment to DNA replication and transcription.It has been reported that several genes including THO complex and splicing endonuclease 1 protein(Senlp)play an important role in regulating R-loop,among which the most important ones are RNase H1 and RNase H2.RNase H can efficiently degrade R-loops by identifing and removing the RNA strand.The THO complex in cells can effectively transport the transcriptional nascent-RNA into the cytoplasm so as to reduce the probability of R-loop formation.SEN1 helicases can specifically open DNA:RNA double-strand.R-loop in the cell is controlled within a reasonable range through the coordination of multiple pathways.We used eukaryote budding yeast Saccharomyces cerevisiae as our experimental material.Saccharomyces cerevisiae are widely used in creating mutates for genetic research among fields of recombination,chromosome separation and expression regulation because it grows quickly,its gene can be easily edited and the single spore of the tetrad is convenient to be separated.In this article,we built R-loop-related rnh1?,rnh2? and hpr1? mutants to check out the defects in meiosis made by R-loop.There is no obvious change in the single mutants,from DNA replication to the survival rate of spores.In the double mutant strain,R-loop level in meiosis obviously increased and finally affects the spore viability.Mutant strains that multiple regulatory pathways interrupted at the same time even showed a prolonged DNA replication and a huge reduction in spore viability.We conclude that R-loop is of great importance to meiosis.The discovery here provided us with a good reference for our further research on the difference of R-loop regulation between mitosis and meiosis.