FellowPhD Silvia Bágeľová Poláková
Project NameCharacterization of novel genes involved in meiotic chromosome segregation.
Host organisationBioscience Center SAS
Duration of the project01.04.2015 - 31.03.2018

Abstract
Sexual reproduction is primarily dependent on meiosis, a special type of cell division, in which the number of sets of chromosomes is reduced to half the original number. It is absolutely essential that the halving of chromosome sets is achieved accurately, because errors in this process can lead to various genetic diseases such as Down Syndrome in humans. The aim of my project is to understand the molecular mechanisms underlying this reduction of the chromosome sets using the fission yeast S. pombe, which is an excellent model organism for studying meiosis. To identify novel genes required for proper segregation of chromosomes during meiosis, I screened a collection of S. pombe knock-out mutants. Out of 3.400 screened mutants, 238 mutants showed chromosome missegregation. At least 30 of these mutants represent novel genes, which have not yet been implicated in meiosis. The functional analysis of two of these proteins Mal3 and Mto1 has been recently published (Polakova et al., 2014). The results of this screening clearly demonstrate that many of the key regulators of meiotic chromosome segregation have not yet been described, and thus open exciting possibilities for future research projects. I have accorded the highest priority to the mutants defective in meiotic recombination, cell cycle regulation and karyogamy because these processes are of fundamental importance from yeast to human cells. I apply a combination of classical molecular and genetic techniques with a multidisciplinary approach such as live-cell imaging, protein complex analysis by mass spectrometry, and high performance liquid chromatography tandem mass spectrometry to decipher the molecular functions of the identified proteins. This research will also lend itself to an expansion of its scope by building upon the idea that many of the identified proteins required for meiosis play important roles in mitosis, and may have significant implications for the diagnosis and treatment of cancer.

Project Summary with Interim Results

Meiosis  produces  haploid  gametes  from  diploid  precursor  cells.  This  reduction  of chromosome number is achieved by two successive divisions after only a single round of DNA replication. To identify novel regulators of meiosis, we screened a library of fission yeast deletion mutants and found that deletion of the dbl2 gene led to missegregation of chromosomes during meiosis. Analysis of live dblcells by fluorescence microscopy showed that chromosomes frequently failed to segregate during the first meiotic division. Further cytological and biochemical analyses revealed that this segregation defect is due to persistent intermediates of DNA double-strand break repair, also called DNA joint molecules. Our results indicate that Dbl2 is required for formation of Fbh1 DNA helicase foci at the sites of DNA double-strand break repair in order to process DNA joint molecules and allow segregation of chromosomes during meiotic divisions. Our bioinformatics searches revealed that Dbl2 is highly conserved in fungi, animals and plants, suggesting that Dbl2 plays a similar role in other organisms – the formation of viable sex cells and healthy progeny.