title: A rolling circle replication mechanism produces multimeric lariats of mitochondrial DNA in Caenorhabditis elegans.
abstract: Mitochondrial DNA (mtDNA) encodes respiratory complex subunits essential to almost all eukaryotes; hence respiratory competence requires faithful duplication of this molecule. However, the mechanism(s) of its synthesis remain hotly debated. Here we have developed Caenorhabditis elegans as a convenient animal model for the study of metazoan mtDNA synthesis. We demonstrate that C. elegans mtDNA replicates exclusively by a phage-like mechanism, in which multimeric molecules are synthesized from a circular template. In contrast to previous mammalian studies, we found that mtDNA synthesis in the C. elegans gonad produces branched-circular lariat structures with multimeric DNA tails; we were able to detect multimers up to four mtDNA genome unit lengths. Further, we did not detect elongation from a displacement-loop or analogue of 7S DNA, suggesting a clear difference from human mtDNA in regard to the site(s) of replication initiation. We also identified cruciform mtDNA species that are sensitive to cleavage by the resolvase RusA; we suggest these four-way junctions may have a role in concatemer-to-monomer resolution. Overall these results indicate that mtDNA synthesis in C. elegans does not conform to any previously documented metazoan mtDNA replication mechanism, but instead are strongly suggestive of rolling circle replication, as employed by bacteriophages. As several components of the metazoan mitochondrial DNA replisome are likely phage-derived, these findings raise the possibility that the rolling circle mtDNA replication mechanism may be ancestral among metazoans.
authors.affiliation: Department of Biology and Interdepartmental Graduate Program in Genetics, Genomics and Bioinformatics, University of California Riverside, Riverside, California, United States of America; BioMediTech and Tampere University Hospital, University of Tampere, Tampere, Finland.
authors.forename: Samantha C
authors.initials: SC
authors.lastname: Lewis
authors.affiliation: BioMediTech and Tampere University Hospital, University of Tampere, Tampere, Finland; Estonian Biocentre, Tartu, Estonia.
authors.forename: Priit
authors.initials: P
authors.lastname: Joers
authors.affiliation: Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America.
authors.forename: Smaranda
authors.initials: S
authors.lastname: Willcox
authors.affiliation: Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America.
authors.forename: Jack D
authors.initials: JD
authors.lastname: Griffith
authors.affiliation: BioMediTech and Tampere University Hospital, University of Tampere, Tampere, Finland; Molecular Neurology Research Program, University of Helsinki, Helsinki, Finland.
authors.forename: Howard T
authors.initials: HT
authors.lastname: Jacobs
authors.affiliation: Department of Biology and Interdepartmental Graduate Program in Genetics, Genomics and Bioinformatics, University of California Riverside, Riverside, California, United States of America.
authors.forename: Bradley C
authors.initials: BC
authors.lastname: Hyman
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics; D004261:DNA Replication / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000096:biosynthesis / Q000235:genetics*; D004259:DNA-Directed DNA Polymerase / Q000235:genetics; D054629:Genome, Mitochondrial; D006066:Gonads / Q000254:growth & development; D006801:Humans; D008928:Mitochondria / Q000235:genetics*; D009097:Multienzyme Complexes / Q000235:genetics; D045522:Recombinases / Q000235:genetics; D000099272:Replisomes
chemical_list: D004272:DNA, Mitochondrial; D004259:DNA-Directed DNA Polymerase; D009097:Multienzyme Complexes; D045522:Recombinases; D000099272:Replisomes