title: Non-random mtDNA segregation patterns indicate a metastable heteroplasmic segregation unit in m.3243A>G cybrid cells.
abstract: Many pathogenic mitochondrial DNA mutations are heteroplasmic, with a mixture of mutated and wild-type mtDNA present within individual cells. The severity and extent of the clinical phenotype is largely due to the distribution of mutated molecules between cells in different tissues, but mechanisms underpinning segregation are not fully understood. To facilitate mtDNA segregation studies we developed assays that measure m.3243A>G point mutation loads directly in hundreds of individual cells to determine the mechanisms of segregation over time. In the first study of this size, we observed a number of discrete shifts in cellular heteroplasmy between periods of stable heteroplasmy. The observed patterns could not be parsimoniously explained by random mitotic drift of individual mtDNAs. Instead, a genetically metastable, heteroplasmic mtDNA segregation unit provides the likely explanation, where stable heteroplasmy is maintained through the faithful replication of segregating units with a fixed wild-type/m.3243A>G mutant ratio, and shifts occur through the temporary disruption and re-organization of the segregation units. While the nature of the physical equivalent of the segregation unit remains uncertain, the factors regulating its organization are of major importance for the pathogenesis of mtDNA diseases.
authors.affiliation: Department of Molecular Cell Biology, Leiden University Medical Centre, Leiden, The Netherlands.
authors.forename: Anton K
authors.initials: AK
authors.lastname: Raap
authors.forename: Roshan S
authors.initials: RS
authors.lastname: Jahangir Tafrechi
authors.forename: Frans M
authors.initials: FM
authors.lastname: van de Rijke
authors.forename: Angela
authors.initials: A
authors.lastname: Pyle
authors.forename: Carolina
authors.initials: C
authors.lastname: Wählby
authors.forename: Karoly
authors.initials: K
authors.lastname: Szuhai
authors.forename: Raimond B G
authors.initials: RB
authors.lastname: Ravelli
authors.forename: René F M
authors.initials: RF
authors.lastname: de Coo
authors.forename: Harsha K
authors.initials: HK
authors.lastname: Rajasimha
authors.forename: Mats
authors.initials: M
authors.lastname: Nilsson
authors.forename: Patrick F
authors.initials: PF
authors.lastname: Chinnery
authors.forename: David C
authors.initials: DC
authors.lastname: Samuels
authors.forename: George M C
authors.initials: GM
authors.lastname: Janssen
mesh_terms: D004272:DNA, Mitochondrial; D019143:Evolution, Molecular; D018740:Genetic Heterogeneity; D042822:Genomic Instability; D006801:Humans; D028361:Mitochondrial Diseases / Q000235:genetics; D008938:Mitosis; D009154:Mutation; D017354:Point Mutation
chemical_list: D004272:DNA, Mitochondrial