Research: Selected projects

External Member: Larsson Adjunct Group

Regulation of mtDNA maintenance

Replication of mammalian mitochondrial DNA (mtDNA) is an essential process that requires high fidelity and control at multiple levels to ensure proper mitochondrial function. The machinery required for mtDNA replication consists of the heterotrimeric mitochondrial DNA polymerase (POLG), the hexameric helicase TWINKLE, the tetrameric mitochondrial single-stranded binding protein (mtSSB) and the mitochondrial RNA polymerase (POLRMT). Besides these basic replisome components, many additional proteins with nuclease, helicase and topoisomerase activities are necessary for mtDNA maintenance. The mitochondrial genome maintenance exonuclease 1 (MGME1; also known as DDK1) is involved in the final steps of mtDNA synthesis and has a role in processing DNA flap structures to allow ligation of the nascent DNA once replication is completed. Mutations in the mitochondrial genome maintenance exonuclease 1 (MGME1) gene were recently reported in patients with mitochondrial disease. To study MGME1 in vivo function, we generated Mgme1 knockout mice and reported that in addition to its role in 5´flap removal this mitochondrial nuclease may have an Important regulatory role at the end of the mtDNA control region (Matic et al., 2018). As a consequence of defective mtDNA replication, the MGME1 homozygous knockouts mice develop mtDNA depletion and accumulate substantial amounts of long linear subgenomic mtDNA molecules in a variety of mouse tissues. Moreover, MGME1 knockout mice display tissue specific replication stalling patterns as revealed by neutral-neutral two-dimensional agarose gel electrophoresis (2DNAGE) and mtDNA sequence coverage patterns obtained by next generation sequencing. These molecular phenotypes emphasize the importance of the MGME1 knockout mouse line as a valuable tool to investigate tissue-specificity of mtDNA maintenance disorders.

In this project we are using MGME1 knockout mice to understand regulatory processes controlling mtDNA manintenance and the tissue-specific manifestations of mtDNA maintenance disorders.

Superassembly of respiratory chain complexes

Respiratory chain dysfunction plays an important role in human disease and aging. It is now well established that the respiratory complexes are highly enriched in the tubular inner mitochondrial membrane invaginations called cristae membranes. The respiratory chain complexes are frequently organized into different types of supermolecular assemblies, denoted supercomplexes. In mitochondria from mammalian tissues, BN-PAGE has revealed supercomplexes of varying stoichiometry including: CI/CIII2/CIV1-4 (a.k.a. respirasomes), CI/CIII2, and CIII2/CIV1-2. Structures for these macromolecular assemblies were recently determined by electron cryo-microscopy, but the reason why supercomplexes exist remains an enigma (Milenkovic et al, 2017). We have shown that C57BL/6 mice, that are widely used in metabolism research, lack a COX7a2l protein and therefore cannot form supercomplex III2IVn. However, this mouse strain nevertheless contains respirasomes and have normal respiratory chain function (Mourier et al, 2014; Pérez-Pérez et al., 2016).

In this project we are investigating the function of respiratory chain supercomplexes in normal physiology and ageing.

Go to Editor View