Understanding crossover control using A. thaliana and S. cerevisiae Public Deposited

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  • March 21, 2019
  • Berchowitz, Luke E.
    • Affiliation: College of Arts and Sciences, Department of Biology
  • During meiosis, homologous chromosomes pair, synapse, and recombine to facilitate accurate chromosome segregation in meiosis I. Meiotic recombination is facilitated by programmed double-strand breaks that can be repaired either as crossovers or non-crossovers. In most organisms, crossover distribution along chromosomes is non-random in that crossovers are more evenly spaced than null expectations. The inhibition of closely spaced events is known as interference. Despite the fact that interference was originally observed almost a century ago, fundamental questions regarding its underlying mechanisms still exist. I discuss key unanswered questions regarding interference as well as the most commonly referenced models that have been proposed to explain the interference mechanism. We have developed a visual assay (the FTL system) for the detection of crossovers, gene conversions and interference in A. thaliana. This assay involves monitoring the segregation of fluorescent proteins in the pollen grains of qrt1 mutants. qrt1 mutants exhibit pollen tetrads i.e. the fusion of the four meiotic products, which allows for advanced statistical analyses previously only available in yeasts. The development and applications of this system are discussed. Humans, S. cerevisiae and A. thaliana have at least two pathways for producing crossovers, which include a primary pathway that is subject to interference and a secondary pathway that is interference-insensitive. Using the FTL system, we demonstrate that AtMUS81 is a mediator of the interference-insensitive pathway in A. thaliana. Atmus81 mutants are sensitive to a wide range of DNA damaging agents and exhibit decreased pollen viability and crossover frequency. The remaining crossovers in the Atmus81 mutant are subject to interference. Meiotic recombination occurs in the context of chromatin and chromatin context is often invoked to explain why recombination occurs preferentially in some genomic regions. Using a technique called FAIRE, we demonstrate that double-strand break hotspots and regions of open chromatin have a positive but complex association in S. cerevisiae. We also show that subtelomeric border regions and regions surrounding tRNA genes are enriched for meiosis-specific open chromatin. Centromeres exhibit constitutive enrichment of open chromatin.
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  • Copenhaver, Gregory
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  • University of North Carolina at Chapel Hill
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