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Meiotic sister chromatid exchanges are rare in C. elegans
David E Almanzar1, Spencer G Gordon1, Ofer Rog1
1School of Biological Sciences, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112-0840, USA.
Current Biology : CB
|March 19, 2021
Summary
Sister chromatid exchanges (SCEs) are rare during meiosis in C. elegans, accounting for less than 2% of DNA repair events. Noncrossover pathways are predominantly used for sister-directed repair, even without homologous chromosomes.
Area of Science:
- Genetics
- Molecular Biology
- Cell Biology
Background:
- Sexual reproduction relies on DNA double-strand break repair for genetic recombination.
- Crossover repair exchanges genetic information but can compromise template integrity, necessitating tight regulation.
- The frequency of sister chromatid exchanges (SCEs) during meiosis has been difficult to quantify due to challenges in distinguishing identical sister chromatids.
Purpose of the Study:
- To directly quantify physiological SCEs in the C. elegans germline.
- To investigate the mechanisms limiting SCEs during meiosis.
- To determine the predominant DNA repair pathways used for sister-directed repair.
Main Methods:
- Developed a technique for selective sister chromatid labeling using 5-ethynyl-2'-deoxyuridine (EdU).
- Directly scored physiological SCEs in the C. elegans germline.
- Assessed SCE frequency in the absence of homologous chromosomes and in mutants for BLM-HIM-6 and the synaptonemal complex.
Main Results:
- SCEs were found to be rare in meiosis, comprising <2% of all DNA repair events.
- SCEs remained infrequent even when homologous chromosomes were absent, indicating a preference for noncrossover pathways.
- Elevated SCEs were observed in the absence of the RecQ helicase BLM-HIM-6.
- The synaptonemal complex, when localized between sister chromatids, promoted SCEs.
Conclusions:
- Sister chromatid repair in C. elegans meiosis predominantly utilizes noncrossover pathways.
- Crossover pathways are primarily used to establish the necessary link between homologous chromosomes.
- BLM-HIM-6 and synaptonemal complex localization are key regulators of SCE frequency.
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