title: Yeast model analysis of novel polymerase gamma variants found in patients with autosomal recessive mitochondrial disease.
abstract: Replication of the mitochondrial genome depends on the single DNA polymerase (pol gamma). Mutations in the POLG gene, encoding the catalytic subunit of the human polymerase gamma, have been linked to a wide variety of mitochondrial disorders that show remarkable heterogeneity, with more than 200 sequence variants, often very rare, found in patients. The pathogenicity and dominance status of many such mutations remain, however, unclear. Remarkable structural and functional conservation of human POLG and its S. cerevisiae ortholog (Mip1p) led to the development of many successful yeast models, enabling to study the phenotype of putative pathogenic mutations. In a group of patients with suspicion of mitochondrial pathology, we identified five novel POLG sequence variants, four of which (p.Arg869Ter, p.Gln968Glu, p.Thr1053Argfs*6, and p.Val1106Ala), together with one previously known but uncharacterised variant (p.Arg309Cys), were amenable to modelling in yeast. Familial analysis indicated causal relationship of these variants with disease, consistent with autosomal recessive inheritance. To investigate the effect of these sequence changes on mtDNA replication, we obtained the corresponding yeast mip1 alleles (Arg265Cys, Arg672Ter, Arg770Glu, Thr809Ter, and Val863Ala, respectively) and tested their effect on mitochondrial genome stability and replication fidelity. For three of them (Arg265Cys, Arg672Ter, and Thr809Ter), we observed a strong, partially dominant phenotype of a complete loss of functional mtDNA, whereas the remaining two led to partial mtDNA depletion and significant increase in point mutation frequencies. These results show good correlation with the severity of symptoms observed in patients and allow to establish these variants as pathogenic mutations.
authors.affiliation: Faculty of Biology, Institute of Genetics and Biotechnology, University of Warsaw, Pawinskiego 5a, 02-106, Warsaw, Poland.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Kaliszewska
authors.forename: Jakub
authors.initials: J
authors.lastname: Kruszewski
authors.forename: Biruta
authors.initials: B
authors.lastname: Kierdaszuk
authors.forename: Anna
authors.initials: A
authors.lastname: Kostera-Pruszczyk
authors.forename: Monika
authors.initials: M
authors.lastname: Nojszewska
authors.forename: Anna
authors.initials: A
authors.lastname: Łusakowska
authors.forename: Joel
authors.initials: J
authors.lastname: Vizueta
authors.forename: Dorota
authors.initials: D
authors.lastname: Sabat
authors.forename: Dorota
authors.initials: D
authors.lastname: Lutyk
authors.forename: Michał
authors.initials: M
authors.lastname: Lower
authors.forename: Dorota
authors.initials: D
authors.lastname: Piekutowska-Abramczuk
authors.forename: Aneta
authors.initials: A
authors.lastname: Kaniak-Golik
authors.forename: Ewa
authors.initials: E
authors.lastname: Pronicka
authors.forename: Anna
authors.initials: A
authors.lastname: Kamińska
authors.forename: Ewa
authors.initials: E
authors.lastname: Bartnik
authors.forename: Paweł
authors.initials: P
authors.lastname: Golik
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Tońska
mesh_terms: D000293:Adolescent; D000483:Alleles; D000595:Amino Acid Sequence; D002675:Child, Preschool; D003001:Cloning, Molecular; D004256:DNA Polymerase I / Q000235:genetics / Q000378:metabolism; D004261:DNA Replication; D004272:DNA, Mitochondrial / Q000235:genetics*; D004259:DNA-Directed DNA Polymerase / Q000235:genetics* / Q000378:metabolism; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D008928:Mitochondria / Q000235:genetics* / Q000378:metabolism; D028361:Mitochondrial Diseases / Q000235:genetics*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010375:Pedigree; D010641:Phenotype; D017354:Point Mutation; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D004272:DNA, Mitochondrial; D029701:Saccharomyces cerevisiae Proteins; D004256:DNA Polymerase I; D004259:DNA-Directed DNA Polymerase; C068352:MIP1 protein, S cerevisiae