MND1 enables repair of two-ended DNA double-strand breaks

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Faithful and timely repair of DNA double-strand breaks (DSBs) is fundamental for the maintenance of genomic integrity. Here, we demonstrate that the meiotic recombination co-factor MND1 facilitates the repair of DSBs in somatic cells. We show that MND1 localizes to DSBs, where it stimulates DNA repair through homologous recombination (HR). Importantly, MND1 is not involved in the response to replication-associated DSBs, implying that it is dispensable for HR-mediated repair of one-ended DSBs. Instead, we find that MND1 specifically plays a role in the response to two-ended DSBs that are induced by IR or various chemotherapeutic drugs, specifically in G2. MND1 localization to DSBs is dependent on resection of the DNA ends, and seemingly occurs through direct binding of MND1 to RAD51-coated ssDNA. Importantly, the lack of MND1-driven HR repair directly potentiates the toxicity of IR-induced damage, which could open new possibilities for therapeutic intervention, specifically in HR-proficient tumors.

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  1. Review coordinated via ASAPbio’s crowd preprint review

    This review reflects comments and contributions by Luciana Gallo, Claudia Molina Pelayo, Sónia Gomes Pereira, Asli Sadli. Review synthesized by Iratxe Puebla.

    The preprint examines the meiotic recombination co-factor MND1 and its role in the repair of double-strand breaks (DSBs) in somatic cells. The paper reports that MND1 stimulates DNA repair through homologous recombination (HR) but is not involved in the response to replication-associated DSBs. MND1 localization to DSBs occurs through direct binding to RAD51-coated ssDNA. MND1 loss potentiates the G2 DNA damage checkpoint and the toxicity of IR-induced damage, opening avenues for therapeutic intervention, particularly in HR-proficient tumors.

    The reviewers raised some minor comments and suggestions on the work:

    Results ‘Therefore, we conclude that MND1-HOP2 are ubiquitously expressed proteins’ - we understand that the study looked at the transcript's expression level and not protein levels, consider revising this sentence.

    Figure 1F - Due to the differences in intensity for the loading control, recommend quantifying the normalized level of MND1.

    we used live-cell imaging of RPE1 cells’- Are these cells p53 KO? In Suppl. Figure 1K, RPE Delpta-p53 cells are used , but the HALO tag was introduced in the normal (WT) RPE cells. Could some clarification be provided for this difference, and report what's the level of MND1 and the effects of its loss in WT RPE cells?

    Analysis of 53BP1 foci formation and resolution in asynchronously growing RPE1 cells revealed that MND1 depletion leads to slower repair and retention of DSBs after IR (Figure 2A, Suppl. Figure 2F&G)’ - While the quantification shown in Figure 2A is explicit, the foci in the raw images displayed in Suppl. Figure 2G appears to be more frequent in the siNT, especially in the last 2 time points. It may be worth making the images bigger and maybe clearer?

    our data show that the role of MND1 in DNA repair is most prominent in G2 phase cells and restricted to repair of two-ended DSBs’ - Can some further context be provided for the last part of this claim. Is this due to the different modes of action of the different drugs used? If so, it would be nice to clarify in the text which drugs induce the two-ended DSBs.

    These data show that MND1 is recruited to sites of DSBs’ - The data shows that there is an increase in MND1 foci, but whether these are or not the sites of DSBs is not clear. Recommend co-staining with a known DSBs marker.


    • Haploid genetic screen - Please describe how cells were fixed.
    • Please detail if/what software was used for the Fisher’s exact test.
    • Cells were fixed after 7 days of growth in 80% methanol and stained with 0.2% crystal violet’ - Please report at which temperature and for how long the steps were completed, and provide a reference for the crystal violet reagent.
    • Membranes were blocked in 5% BSA’ - Please report the temperature and duration for this step.
    • Please describe how the propidium iodide staining was performed.