Abstract
The number and distribution of crossover events are tightly regulated at prophase of meiosis I. The resolution of Holliday junctions by structure-specific endonucleases, including MUS-81, SLX-1, XPF-1 and GEN-1, is one of the main mechanisms proposed for crossover formation. However, how these nucleases coordinately resolve Holliday junctions is still unclear. Here we identify both the functional overlap and differences between these four nucleases regarding their roles in crossover formation and control in the Caenorhabditis elegans germline. We show that MUS-81, XPF-1 and SLX-1, but not GEN-1, can bind to HIM-18/SLX4, a key scaffold for nucleases. Analysis of synthetic mitotic defects revealed that MUS-81 and SLX-1, but not XPF-1 and GEN-1, have overlapping roles with the Bloom syndrome helicase ortholog, HIM-6, supporting their in vivo roles in processing recombination intermediates. Taking advantage of the ease of genetic analysis and high-resolution imaging afforded by C. elegans, we examined crossover designation, frequency, distribution and chromosomal morphology in single, double, triple and quadruple mutants of the structure-specific endonucleases. This revealed that XPF-1 functions redundantly with MUS-81 and SLX-1 in executing crossover formation during meiotic double-strand break repair. Analysis of crossover distribution revealed that SLX-1 is required for crossover suppression at the center region of the autosomes. Finally, analysis of chromosome morphology in oocytes at late meiosis I stages uncovered that SLX-1 and XPF-1 promote meiotic chromosomal stability by preventing formation of chromosomal abnormalities. We propose a model in which coordinate action between structure-specific nucleases at different chromosome domains, namely MUS-81, SLX-1 and XPF-1 at the arms and SLX-1 at the center region, exerts positive and negative regulatory roles, respectively, for crossover control during C. elegans meiosis.
Highlights
Structure-specific endonucleases are required for several kinds of DNA repair processes such as nucleotide excision repair (NER), DNA interstrand crosslink repair (ICL) and double-strand break repair (DSBR)
We cannot rule out the possibility that post-translational modificationdependent interactions might have been missed in a yeast twohybrid assay. These data suggest that the structure-specific endonucleases identified far can be categorized into two classes, one consisting of HIM-18-associated nucleases (SLX-1, XPF-1 and MUS-81) and the second consisting of GEN-1
We found that HIM-18/SLX-4 interacts with SLX-1, XPF-1 and MUS-81 by yeast two-hybrid
Summary
Structure-specific endonucleases are required for several kinds of DNA repair processes such as nucleotide excision repair (NER), DNA interstrand crosslink repair (ICL) and double-strand break repair (DSBR). Homologous recombination is an error free repair pathway because the broken DNA ends are repaired from templates consisting of either homologous sequence at the sister chromatids or the homologous chromosomes. At least one DNA double-strand break has to be repaired as a crossover (obligate crossover) by homologous recombination between non-sister chromatids of a homologous pair of chromosomes. The double (or single) Holliday junction is believed to be the intermediate required to make a crossover product [1]. The opposite sense resolution of the double Holliday junction results in crossover products, while the same sense resolution results in noncrossover products [2]. The convergent branch migration and decatenation of such intermediates, referred to as double
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