bims-mitran 2022-05-01 papers

Issue of 2022–05–01
four papers selected by
Andreas Kohler, Stockholm University

Cell. 2022 Apr 18. pii: S0092-8674(22)00389-0. [Epub ahead of print]

Targeted A-to-G base editing in human mitochondrial DNA with programmable deaminases.

Sung-Ik Cho, Seonghyun Lee, Young Geun Mok, Kayeong Lim, Jaesuk Lee, Ji Min Lee, Eugene Chung, Jin-Soo Kim.

Mitochondrial DNA (mtDNA) editing paves the way for disease modeling of mitochondrial genetic disorders in cell lines and animals and also for the treatment of these diseases in the future. Bacterial cytidine deaminase DddA-derived cytosine base editors (DdCBEs) enabling mtDNA editing, however, are largely limited to C-to-T conversions in the 5'-TC context (e.g., TC-to-TT conversions), suitable for generating merely 1/8 of all possible transition (purine-to-purine and pyrimidine-to-pyrimidine) mutations. Here, we present transcription-activator-like effector (TALE)-linked deaminases (TALEDs), composed of custom-designed TALE DNA-binding arrays, a catalytically impaired, full-length DddA variant or split DddA originated from Burkholderia cenocepacia, and an engineered deoxyadenosine deaminase derived from the E. coli TadA protein, which induce targeted A-to-G editing in human mitochondria. Custom-designed TALEDs were highly efficient in human cells, catalyzing A-to-G conversions at a total of 17 target sites in various mitochondrial genes with editing frequencies of up to 49%.

Keywords: DNA; DddAtox; TALED; adenine deaminase; base editing; genome editing; mitochondria; organelle

DOI: https://doi.org/10.1016/j.cell.2022.03.039

Nat Commun. 2022 Apr 29. 13(1): 2340

Mitofusin 1 and 2 regulation of mitochondrial DNA content is a critical determinant of glucose homeostasis.

Vaibhav Sidarala, Jie Zhu, Elena Levi-D'Ancona, Gemma L Pearson, Emma C Reck, Emily M Walker, Brett A Kaufman, Scott A Soleimanpour.

The dynamin-like GTPases Mitofusin 1 and 2 (Mfn1 and Mfn2) are essential for mitochondrial function, which has been principally attributed to their regulation of fission/fusion dynamics. Here, we report that Mfn1 and 2 are critical for glucose-stimulated insulin secretion (GSIS) primarily through control of mitochondrial DNA (mtDNA) content. Whereas Mfn1 and Mfn2 individually were dispensable for glucose homeostasis, combined Mfn1/2 deletion in β-cells reduced mtDNA content, impaired mitochondrial morphology and networking, and decreased respiratory function, ultimately resulting in severe glucose intolerance. Importantly, gene dosage studies unexpectedly revealed that Mfn1/2 control of glucose homeostasis was dependent on maintenance of mtDNA content, rather than mitochondrial structure. Mfn1/2 maintain mtDNA content by regulating the expression of the crucial mitochondrial transcription factor Tfam, as Tfam overexpression ameliorated the reduction in mtDNA content and GSIS in Mfn1/2-deficient β-cells. Thus, the primary physiologic role of Mfn1 and 2 in β-cells is coupled to the preservation of mtDNA content rather than mitochondrial architecture, and Mfn1 and 2 may be promising targets to overcome mitochondrial dysfunction and restore glucose control in diabetes.

DOI: https://doi.org/10.1038/s41467-022-29945-7

RNA Biol. 2022 Jan;19(1): 662-677

Mechanisms of ribosome recycling in bacteria and mitochondria: a structural perspective.

Savannah M Seely, Matthieu G Gagnon.

In all living cells, the ribosome translates the genetic information carried by messenger RNAs (mRNAs) into proteins. The process of ribosome recycling, a key step during protein synthesis that ensures ribosomal subunits remain available for new rounds of translation, has been largely overlooked. Despite being essential to the survival of the cell, several mechanistic aspects of ribosome recycling remain unclear. In eubacteria and mitochondria, recycling of the ribosome into subunits requires the concerted action of the ribosome recycling factor (RRF) and elongation factor G (EF-G). Recently, the conserved protein HflX was identified in bacteria as an alternative factor that recycles the ribosome under stress growth conditions. The homologue of HflX, the GTP-binding protein 6 (GTPBP6), has a dual role in mitochondrial translation by facilitating ribosome recycling and biogenesis. In this review, mechanisms of ribosome recycling in eubacteria and mitochondria are described based on structural studies of ribosome complexes.

Keywords: GTPBP6; HflX; Ribosome; elongation factor G; protein synthesis; ribosome recycling; ribosome recycling factor; tRNA; translation factors

DOI: https://doi.org/10.1080/15476286.2022.2067712

Acta Neuropathol. 2022 Apr 30.

Heteroplasmic mitochondrial DNA mutations in frontotemporal lobar degeneration.

Yu Nie, Alexander Murley, Zoe Golder, James B Rowe, Kieren Allinson, Patrick F Chinnery.

Frontotemporal lobar degeneration (FTLD) is a common cause of young onset dementia and is characterised by focal neuropathology. The reasons for the regional neuronal vulnerability are not known. Mitochondrial mechanisms have been implicated in the pathogenesis of FTLD, raising the possibility that frontotemporal regional mutations of mitochondrial DNA (mtDNA) are contributory causes. Here we applied dual sequencing of the entire mtDNA at high depth to identify high-fidelity single nucleotide variants (mtSNVs) and mtDNA rearrangements in post mortem brain tissue of people affected by FTLD and age-matched controls. Both mtSNVs and mtDNA rearrangements were elevated in the temporal lobe, with the greatest burden seen in FTLD. mtSNVs found in multiple brain regions also reached a higher heteroplasmy levels in the temporal lobe. The temporal lobe of people with FTLD had a higher burden of ribosomal gene variants predicted to affect intra-mitochondrial protein synthesis, and a higher proportion of missense variants in genes coding for respiratory chain subunits. In conclusion, heteroplasmic mtDNA variants predicted to affect oxidative phosphorylation are enriched in FTLD temporal lobe, and thus may contribute to the regional vulnerability in pathogenesis.

DOI: https://doi.org/10.1007/s00401-022-02423-6