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Coordination of Oxidative Stress Signalling with Forkhead-Regulated Transcription during the Fission Yeast Cell Cycle

Final Report Summary - OXICELLCYCLE (Coordination of Oxidative Stress Signalling with Forkhead-Regulated Transcription during the Fission Yeast Cell Cycle)

This project aimed to characterise with more detail the reproductive isolation mechanism that exist between the different wild isolates of S. pombe. The study of the evolutionary processes responsible for reproductive isolation have been an active field of research in other model organism like Drosophila species and Saccharomyces sensu stricto species (for reviews see [1]), but has only been rarely studied for Schizosaccharomyces species [2]. From the studies carried out in the Saccharomyces sensu stricto species several mechanism responsible for reproductive isolation have been detected in those yeast species [3]. Fission yeast well established model organism and is only distantly related to Saccharomyces genus. On top of that, fission yeast is a haploid organism with a diploid growth only in a transient stage, while Saccharomyces species are often diploids. Altogether this suggest that fission yeast will be a valuable model organism to get more insight into the study of the speciation.

The main objective of that project will be to introduce to the research community fission yeast as a powerful organism to study speciation events. This will be relevant for both evolutionary biologist, to get new insights and complement what is already known in the field, and fission yeast community, by introducing evolution as a field of research in the community.

In this project we have created a collection of fission yeast diploid hybrids obtained from the crosses of different wild isolates available from microorganism collections all over the world. Sporulation was induced on those diploid hybrids, and spore survival was determined by Random Spore Survival (RSA) or tetrad analysis following protocols described at [4]. Spore survival observed strongly correlates with the degree of sequence variation of the parental strains.

Detailed maps of chromosome recombination were obtained for some of the crosses analysed in this study. This study show that while the number of crossover per genome is reduced in crosses involving distantly related strains of S. pombe this is not true when analysing meiosis of diploid hybrids obtained from closely related fission yeast strains. This observation suggest that in fission yeast, as observed in Saccharomyces species and prokaryotic organism [5] [6], mismatch repair proteins could be involved into the reinforcement of reproductive isolation mechanism.

Preliminary studies to determine the existence of pairs of Dobzhansky-Muller incompatible alleles have been initiated as result of this project. The analysis by deep sequencing of the proportion of reads originating from both parental strains allowed us to identify candidate regions that show a significant deviation from the expected 2:2 ratio. This finding will allow us to define more concrete research approaches to tackle whether there are incompatibilities between wild isolates of fission yeast that affects the reproductive isolation, and eventually study the molecular mechanism responsible for the incompatibilities observed.

1. Louis, Edward J (2009) 'Evolutionary genetics: Origins of reproductive isolation..' Nature, 457(7229)29th January, pp. 549-550.
2. Kondrat'eva, V I and Naumov, G I (2001) 'The phenomenon of spore killing in Schizosaccharomyces pombe hybrids..' Doklady biological sciences : proceedings of the Academy of Sciences of the USSR, Biological sciences sections / translated from Russian, 379, pp. 385-388.
3. Greig, D (2009) 'Reproductive isolation in Saccharomyces..' Heredity, 102(1), pp. 39-44.
4. Forsburg, Susan L and Rhind, Nicholas (2006) 'Basic methods for fission yeast.' Yeast (Chichester, England), 23(3), pp. 173-183.
5. Hunter, N, Chambers, S R, Louis, E J and Borts, R H (1996) 'The mismatch repair system contributes to meiotic sterility in an interspecific yeast hybrid..' The EMBO Journal, 15(7), pp. 1726-1733.
6. Rayssiguier, C, Thaler, D S and Radman, M (1989) 'The barrier to recombination between Escherichia coli and Salm.