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DNA ligase III is critical for mtDNA integrity but not Xrcc1-mediated nuclear DNA repair


DNA replication and repair in mammalian cells involves three distinct DNA ligases: ligase I (Lig1), ligase III (Lig3) and ligase IV (Lig4)1. Lig3 is considered a key ligase during base excision repair because its stability depends upon its nuclear binding partner Xrcc1, a critical factor for this DNA repair pathway2,3. Lig3 is also present in the mitochondria, where its role in mitochondrial DNA (mtDNA) maintenance is independent of Xrcc1 (ref. 4). However, the biological role of Lig3 is unclear as inactivation of murine Lig3 results in early embryonic lethality5. Here we report that Lig3 is essential for mtDNA integrity but dispensable for nuclear DNA repair. Inactivation of Lig3 in the mouse nervous system resulted in mtDNA loss leading to profound mitochondrial dysfunction, disruption of cellular homeostasis and incapacitating ataxia. Similarly, inactivation of Lig3 in cardiac muscle resulted in mitochondrial dysfunction and defective heart-pump function leading to heart failure. However, Lig3 inactivation did not result in nuclear DNA repair deficiency, indicating essential DNA repair functions of Xrcc1 can occur in the absence of Lig3. Instead, we found that Lig1 was critical for DNA repair, but acted in a cooperative manner with Lig3. Additionally, Lig3 deficiency did not recapitulate the hallmark features of neural Xrcc1 inactivation such as DNA damage-induced cerebellar interneuron loss6, further underscoring functional separation of these DNA repair factors. Therefore, our data reveal that the critical biological role of Lig3 is to maintain mtDNA integrity and not Xrcc1-dependent DNA repair.

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Figure 1: Lig3 inactivation throughout the nervous system leads to a phenotype different to Xrcc1 loss.
Figure 2: Mitochondrial function is disrupted in the Lig3 Nes-cre brain.
Figure 3: Lig3 inactivation causes cardiac failure associated with defective mitochondrial function.
Figure 4: Lig3 is not essential for nuclear DNA repair.


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We thank the Hartwell Center for biotechnology support, the Transgenic Core Facility for blastocyst injections and the Animal Resources Center for animal husbandry. We also acknowledge the Light Microscopy Core, the Electron Microscopy Core and C. Calabrese and the Animal Imaging Core for magnetic resonance imaging and echocardiography analysis. P.J.M. is supported by the National Institutes of Health (NS-37956, CA-21765), a Cancer Center Support Grant (P30 CA21765) and the American Lebanese and Syrian Associated Charities of St Jude Children’s Research Hospital. S.K. is a Neoma Boadway AP Endowed Fellow.

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Authors and Affiliations



Y.G., S.K. and Y.L. performed all experiments characterizing the Lig3-deficient mouse and contributed to writing the manuscript. Y.G. and H.R.R. generated the targeted embryonic stem cells for blastocyst injection and were responsible for colony production and maintenance with assistance from S.K. and Y.L. S.K. and J.Z. established the functional analyses of ligases. J.E.R. provided pathology analysis. P.J.M. was project leader and produced the final version of the manuscript.

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Correspondence to Peter J. McKinnon.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Figures

The file contains Supplementary Figures 1-8 with legends. (PDF 9838 kb)

Supplementary Movie 1

This movie shows three Lig3Nes-cre mice at twelve days of age (P12) that have developed profound ataxia, compared with a wild-type littermate. (MOV 15516 kb)

Supplementary Movie 2

This movie shows loss of Lig3 affects mitochondrial function, using Mitotracker Red staining of astrocytes isolated from the Lig3Nes-cre brain by live-cell confocal imaging. While control astrocytes show a pattern of streaming mitochondria, the Lig3 mutant cells show altered mitochondrial dynamics with a static and pulsating appearance. (MOV 7322 kb)

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Gao, Y., Katyal, S., Lee, Y. et al. DNA ligase III is critical for mtDNA integrity but not Xrcc1-mediated nuclear DNA repair. Nature 471, 240–244 (2011).

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