bims-mitran 2022-11-13 papers

Issue of 2022–11–13
two papers selected by
Andreas Kohler, University of Graz

J Cell Biol. 2023 Jan 02. pii: e202201137. [Epub ahead of print]222(1):

REC drives recombination to repair double-strand breaks in animal mtDNA.

Anna Klucnika, Peiqiang Mu, Jan Jezek, Matthew McCormack, Ying Di, Charles R Bradshaw, Hansong Ma.

Mechanisms that safeguard mitochondrial DNA (mtDNA) limit the accumulation of mutations linked to mitochondrial and age-related diseases. Yet, pathways that repair double-strand breaks (DSBs) in animal mitochondria are poorly understood. By performing a candidate screen for mtDNA repair proteins, we identify that REC-an MCM helicase that drives meiotic recombination in the nucleus-also localizes to mitochondria in Drosophila. We show that REC repairs mtDNA DSBs by homologous recombination in somatic and germline tissues. Moreover, REC prevents age-associated mtDNA mutations. We further show that MCM8, the human ortholog of REC, also localizes to mitochondria and limits the accumulation of mtDNA mutations. This study provides mechanistic insight into animal mtDNA recombination and demonstrates its importance in safeguarding mtDNA during ageing and evolution.

DOI: https://doi.org/10.1083/jcb.202201137

Nucleic Acids Res. 2022 Nov 09. pii: gkac1028. [Epub ahead of print]

Selective degradation of tRNASer(AGY) is the primary driver for mitochondrial seryl-tRNA synthetase-related disease.

Tingting Yu, Yi Zhang, Wen-Qiang Zheng, Siqi Wu, Guoqiang Li, Yong Zhang, Niu Li, Ruen Yao, Pengfei Fang, Jian Wang, Xiao-Long Zhou.

Mitochondrial translation is of high significance for cellular energy homeostasis. Aminoacyl-tRNA synthetases (aaRSs) are crucial translational components. Mitochondrial aaRS variants cause various human diseases. However, the pathogenesis of the vast majority of these diseases remains unknown. Here, we identified two novel SARS2 (encoding mitochondrial seryl-tRNA synthetase) variants that cause a multisystem disorder. c.654-14T > A mutation induced mRNA mis-splicing, generating a peptide insertion in the active site; c.1519dupC swapped a critical tRNA-binding motif in the C-terminus due to stop codon readthrough. Both mutants exhibited severely diminished tRNA binding and aminoacylation capacities. A marked reduction in mitochondrial tRNASer(AGY) was observed due to RNA degradation in patient-derived induced pluripotent stem cells (iPSCs), causing impaired translation and comprehensive mitochondrial function deficiencies. These impairments were efficiently rescued by wild-type SARS2 overexpression. Either mutation caused early embryonic fatality in mice. Heterozygous mice displayed reduced muscle tissue-specific levels of tRNASers. Our findings elucidated the biochemical and cellular consequences of impaired translation mediated by SARS2, suggesting that reduced abundance of tRNASer(AGY) is a key determinant for development of SARS2-related diseases.

DOI: https://doi.org/10.1093/nar/gkac1028