NBS1 is required for SPO11-linked DNA double-strand break repair in male meiosis

Bin Zhang,Zhenghui Tang,Lejun Li,Lin-Yu Lu

doi:10.1038/s41418-020-0493-4

Abstract

DNA double-strand breaks (DSBs) pose a serious threat to genomic stability. Paradoxically, hundreds of programed DSBs are generated by SPO11 in meiotic prophase, which are exclusively repaired by homologous recombination (HR) to promote obligate crossover between homologous chromosomes. In somatic cells, MRE11-RAD50-NBS1 (MRN) complex-dependent DNA end resection is a prerequisite for HR repair, especially for DSBs that are covalently linked with proteins or chemicals. Interestingly, all meiotic DSBs are linked with SPO11 after being generated. Although MRN complex’s function in meiotic DSB repair has been established in lower organisms, the role of MRN complex in mammalian meiotic DSB repair is not clear. Here, we show that MRN complex is essential for repairing meiotic SPO11-linked DSBs in male mice. In male germ cells, conditional inactivation of NBS1, a key component of MRN complex, causes dramatic reduction of DNA end resection and defective HR repair in meiotic prophase. NBS1 loss severely disrupts chromosome synapsis, generates abnormal chromosome structures, and eventually leads to meiotic arrest and male infertility in mice. Unlike in somatic cells, the recruitment of NBS1 to SPO11-linked DSB sites is MDC1-independent but requires other phosphorylated proteins. Collectively, our study not only reveals the significance of MRN complex in repairing meiotic DSBs but also discovers a unique mechanism that recruits MRN complex to SPO11-linked DSB sites.

Highlights

DNA double-strand breaks (DSBs) are the most deleterious DNA damage in cells
Consistent with the idea that TOP2-linked DSBs are predominantly repaired through nonhomologous end joining (NHEJ), TDP2 KO cells are more sensitive to etoposide than NBS1 depletion (Fig. 1b, d, g)
We have shown that conditional inactivation of NBS1 in germ cells leads to meiotic arrest and male infertility

Summary

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DNA double-strand breaks (DSBs) are the most deleterious DNA damage in cells. DSBs can be repaired by either nonhomologous end joining (NHEJ) or homologous recombination (HR) [1, 2]. Since EXO1 or DNA2 cannot directly process DSBs that are covalently linked to proteins or chemicals, MRN complex-dependent endocleavage is required for resection of this type of DSBs. In somatic cells, Topoisomerase II (TOP2) resolves DNA catenanes during DNA replication and transcription by transiently cutting and ligating DNA [9]. TDP2 loss in mice does not affect meiotic progression or fertility, suggesting that NHEJ is not used for repairing meiotic SPO11linked DSBs [14]. To examine the function of MRN complex in meiotic DSB repair in mice, we conditionally inactivate NBS1 in germ cells. NBS1 loss compromises the repair of SPO11-linked DSBs, disrupts chromosome synapsis, generates abnormal chromosome structures, and eventually leads to meiotic arrest and male infertility

Results

Discussion

Materials and methods

Compliance with ethical standards