Formation of interference-sensitive meiotic cross-overs requires sufficient DNA leading-strand elongation
Monday, 2015/10/12 | 07:52:58
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Jiyue Huang, Zhihao Cheng, Cong Wang, Yue Hong, Hang Su, Jun Wang, Gregory P. Copenhaver, Hong Ma, and Yingxiang Wang PLANT BIOLOGY SignificanceMeiosis is essential for eukaryotic sexual reproduction, and meiotic recombination redistributes genetic variations among progeny. Homologous recombination is also important for DNA repair and genome stability. Current recombination models include DNA synthesis, particularly leading-strand synthesis, but its role has not been tested experimentally. Here, we showed that mutations in a DNA polymerase required for leading-strand elongation caused reduced fertility, defects in meiotic chromosome fragmentation and segregation, and reduction of interference-sensitive cross-overs (COs). Because the majority of meiotic COs are produced from the interference-sensitive pathway in budding yeast, mammals, and flowering plants, the discovery of leading-strand elongation in the differentiation of meiotic recombination pathways has important implications in understanding of human reproductive health and crop breeding. AbstractMeiosis halves diploid genomes to haploid and is essential for sexual reproduction in eukaryotes. Meiotic recombination ensures physical association of homologs and their subsequent accurate segregation and results in the redistribution of genetic variations among progeny. Most organisms have two classes of cross-overs (COs): interference-sensitive (type I) and -insensitive (type II) COs. DNA synthesis is essential for meiotic recombination, but whether DNA synthesis has a role in differentiating meiotic CO pathways is unknown. Here, we show that Arabidopsis POL2A, the homolog of the yeast DNA polymerase-ε (a leading-strand DNA polymerase), is required for plant fertility and meiosis. Mutations in POL2A cause reduced fertility and meiotic defects, including abnormal chromosome association, improper chromosome segregation, and fragmentation. Observation of prophase I cell distribution suggests that pol2a mutants likely delay progression of meiotic recombination. In addition, the residual COs in pol2a have reduced CO interference, and the double mutant of pol2a with mus81, which affects type II COs, displayed more severe defects than either single mutant, indicating that POL2A functions in the type I pathway. We hypothesize that sufficient leading-strand DNA elongation promotes formation of some type I COs. Given that meiotic recombination and DNA synthesis are conserved in divergent eukaryotes, this study and our previous study suggest a novel role for DNA synthesis in the differentiation of meiotic recombination pathways.
See: http://www.pnas.org/content/112/40/12534.abstract.html?etoc PNAS October 6, 2015; vol. 112 no. 40 12534–12539
Fig. 4. POL2A is not required for DSB formation but promotes progression of meiotic recombination. (A) Immunostaining with γ-H2AX (red), RAD51 (green), and DAPI counterstain (blue) at zygotene and pachytene in the WT and pol2a-1. (Scale bar: 5 μm.) (B) Variation of the γ-H2AX and RAD51 foci numbers above shown by boxplot in the WT and pol2a-1. **P ≤ 0.01 with a one-tailed Student t test. (C) Percentages of leptotene, zygotene, and pachytene cells at ZT4 (4 h after lights on), ZT5, ZT6, and ZT7, with error bars from analyses of three to five biological replicates in the WT, pol2a-1, and pol2a-2.
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