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.