Mitochondrial DNA maintenance


Human mitochondrial DNA (mtDNA), ‘our other genome’, was fully sequenced in 1981 and represents a separate genome present from several hundreds to thousands of copies per cell.  It encodes thirteen protein subunits of the respiratory chain and ATP synthase, plus the 2 rRNAs and 22 tRNAs required for their synthesis on mitochondrial ribosomes (See the figure below). The 13 mtDNA encoded proteins are subunits of four of the five oxidative phosphorylation complexes and therefore indispensible for cellular energy production. Maintenance of an intact mitochondrial genome is therefore essential for viability and for the completion of development. In mammals, mtDNA is exclusively inherited via the maternal line, thus mtDNA disease mutations are solely transmitted from mother to offspring.  MtDNA disease mutations can be classified as maternally inherited or ‘spontaneous’ germline mutations, but can also be the consequence of mutations in nuclear genes coding for proteins involved in mtDNA maintenance. In the latter case, the disease is often restricted to some tissues and does not normally affect the female germline. Inheritance is thus Mendelian and most nuclear ‘mtDNA disease’ genes have been identified using the rationale of Mendelian disease genetics.

MtDNA is organized in foci, termed nucleoids, as small assemblies containing 2-10 mtDNA copies and various proteins that are poorly conserved in evolution. Despite a renewed interest in mtDNA due to its involvement in human disease and ageing, there are still many fundamental questions surrounding faithful copying (replication), repair and inheritance of mtDNA in humans. My laboratory aims to address these questions in part via the identification and characterization of those mitochondrial proteins that associate with nucleoids or play a role in their biology, that is to say we concentrate on the machineries in the cell and the mitochondrion that are involved in the maintenance of mtDNA in all its aspects. Ultimately, the aim is not only to understand the very basic molecular biology of for example mtDNA replication and repair and individual nucleoid proteins but to also understand mtDNA maintenance at the cell biological and organismal level. This will not only provide fundamental insight in one of the least understood processes in the cell, it will also provide a framework to understand and possibly treat mtDNA disease.

Recent publications

  1. TCA Cycle and Mitochondrial Membrane Potential Are Necessary for Diverse Biological Functions. Martínez-Reyes I, Diebold LP, Kong H, Schieber M, Huang H, Hensley CT, Mehta MM, Wang T, Santos JH, Woychik R, Dufour E, Spelbrink JN, Weinberg SE, Zhao Y, DeBerardinis RJ, Chandel NS. Mol Cell. 2016 Jan 21;61(2):199-209.

  2. Human Mitochondrial DNA-Protein Complexes Attach to a Cholesterol-Rich Membrane Structure. Gerhold JM, Cansiz-Arda Ş, Lõhmus M, Engberg O, Reyes A, van Rennes H, Sanz A, Holt IJ, Cooper HM, Spelbrink JN.  Sci Rep. 2015 Oct 19;5:15292.

  3. The hexameric structure of the human mitochondrial replicative helicase Twinkle. Fernández-Millán P, Lázaro M, Cansız-Arda Ş, Gerhold JM, Rajala N, Schmitz CA, Silva-Espiña C, Gil D, Bernadó P, Valle M, Spelbrink JN, Solà M. Nucleic Acids Res. 2015 Apr 30;43(8):4284-95.

  4. Whole cell formaldehyde cross-linking simplifies purification of mitochondrial nucleoids and associated proteins involved in mitochondrial gene expression. Rajala N, Hensen F, Wessels HJ, Ives D, Gloerich J, Spelbrink JN. PLoS One. 2015 Feb 19;10(2):e0116726.

  5. Replication factors transiently associate with mtDNA at the mitochondrial inner membrane to facilitate replication. Rajala N, Gerhold JM, Martinsson P, Klymov A, Spelbrink JN. Nucleic Acids Res. 2014 Jan;42(2):952-67

  6. Functional organization of mammalian mitochondrial DNA in nucleoids: history, recent developments, and future challenges. Spelbrink JN. IUBMB Life. 2010 Jan;62(1):19-32

  7. The human SIRT3 protein deacetylase is exclusively mitochondrial. Cooper HM, Spelbrink JN. Biochem J. 2008 Apr 15;411(2):279-85

  8. Expression of catalytic mutants of the mtDNA helicase Twinkle and polymerase POLG causes distinct replication stalling phenotypes. Wanrooij S, Goffart S, Pohjoismäki JL, Yasukawa T, Spelbrink JN. Nucleic Acids Res. 2007;35(10):3238-51

  9. Human mitochondrial DNA deletions associated with mutations in the gene encoding Twinkle, a phage T7 gene 4-like proteinlocalized in mitochondria. Spelbrink JN, Li FY, Tiranti V, Nikali K, Yuan QP, Tariq M, Wanrooij S, Garrido N, Comi G, Morandi L, Santoro L, Toscano A, Fabrizi GM, Somer H, Croxen R, Beeson D, Poulton J, Suomalainen A, Jacobs HT, Zeviani M, Larsson C. Nat Genet. 2001 Jul;28(3):223-31