Meiotic DNA break repair can utilize homolog-independent chromatid templates in C. elegans

Erik Toraason,Anna Horacek,Cordell Clark,Marissa L Glover,Victoria L Adler,Tolkappiyan Premkumar,Alina Salagean,Francesca Cole,Diana E Libuda

doi:10.1016/j.cub.2021.03.008

Erik Toraason, Anna Horacek + Show 7 more

Open Access

https://doi.org/10.1016/j.cub.2021.03.008

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Abstract

During meiosis, the maintenance of genome integrity is critical for generating viable haploid gametes.1 In meiotic prophase I, double-strand DNA breaks (DSBs) are induced and a subset of these DSBs are repaired as interhomolog crossovers to ensure proper chromosome segregation. DSBs not resolved as crossovers with the homolog must be repaired by other pathways to ensure genome integrity.2 To determine if alternative repair templates can be engaged for meiotic DSB repair during oogenesis, we developed an assay to detect sister and/or intra-chromatid repair events at a defined DSB site during Caenorhabditis elegans meiosis. Using this assay, we directly demonstrate that the sister chromatid or the same DNA molecule can be engaged as a meiotic repair template for both crossover and noncrossover recombination, with noncrossover events being the predominant recombination outcome. We additionally find that the sister or intra-chromatid substrate is available as a recombination partner for DSBs induced throughout meiotic prophase I, including late prophase when the homolog is unavailable. Analysis of noncrossover conversion tract sequences reveals that DSBs are processed similarly throughout prophase I. We further present data indicating that the XPF-1 nuclease functions in late prophase to promote sister or intra-chromatid repair at steps of recombination following joint molecule processing. Despite its function in sister or intra-chromatid repair, we find that xpf-1 mutants do not exhibit severe defects in progeny viability following exposure to ionizing radiation. Overall, we propose that C.elegans XPF-1 may assist as an intersister or intrachromatid resolvase only in late prophase I.

Highlights

Several studies have hypothesized that after access to the homolog is shut down, there is a regulated switch in template preference from the homolog to the sister chromatid during late meiotic prophase I to ensure the repair of any remaining DSBs prior to the meiotic divisions.[4,5,6]
Studies in Saccharomyces cerevisiae indicate the sister chromatid can be engaged during meiosis,[7] and multiple lines of evidence have suggested that the sister chromatid may be engaged as a meiotic DSB repair template to repair these remaining DSBs in metazoan meiosis,[4,5,8] but the perfect sequence identity shared between sister chromatids has precluded direct testing of this hypothesis in metazoans
To determine whether the sister chromatid or the same chromatid can be engaged as a repair template during C. elegans meiosis, we developed a non-allelic intersister/intrachromatid repair assay (ICR assay; Figures 1A and S1) that utilizes controlled excision of a Mos[1] transposon to induce a single DSB within a genetic reporter that detects repair events using a non-allelic truncated cassette on the sister chromatid or same chromatid as a template

Summary

Introduction

To determine whether the sister chromatid or the same chromatid can be engaged as a repair template during C. elegans meiosis, we developed a non-allelic intersister/intrachromatid repair assay (ICR assay; Figures 1A and S1) that utilizes controlled excision of a Mos[1] transposon to induce a single DSB within a genetic reporter that detects repair events using a non-allelic truncated cassette on the sister chromatid or same chromatid as a template.

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