Project description:How mitochondrial DNA (mtDNA) polymorphisms influence complex phenotypes remains poorly understood. Using Mitochondrial-Nuclear eXchange (MNX) mice, we previously showed that mtDNA single nucleotide polymorphisms (SNP) modify metastasis, cardiovascular disease, and epigenetic marks independently of metabolic differences, suggesting a role for non-protein-coding loci. The only SNP correlating with these phenotypes resides in the gene encoding mitochondrial tRNA-Arginine (mt-tRNAArg (UCG), mt-TR). Here we identify and preliminarily characterize previously undescribed tRNA-derived fragments (tRF) generated from mt-TR. Northern blotting revealed distinct tRF that are differentially expressed between lung and liver and between sexes. Small RNA sequencing failed to capture these tRF unless samples were pre-treated to enzymatically remove non-canonical RNA termini and base methylation. Focusing on fragments with complete homology to mt-TR, the two most abundant tRF align uniquely to the mitochondrial genome and share conserved cleavage sites. Together, these findings uncover mitochondrial-derived tRF as a previously unrecognized small RNA metastasis modifiers and expand the functional output of the mitochondrial genome, supporting a model in which mtDNA-encoded tRF contribute to phenotype modification.
Project description:How mitochondrial DNA (mtDNA) polymorphisms influence complex phenotypes remains poorly understood. Using Mitochondrial-Nuclear eXchange (MNX) mice, we previously showed that mtDNA single nucleotide polymorphisms (SNP) modify metastasis, cardiovascular disease, and epigenetic marks independently of metabolic differences, suggesting a role for non-protein-coding loci. The only SNP correlating with these phenotypes resides in the gene encoding mitochondrial tRNA-Arginine (mt-tRNAArg (UCG), mt-TR). Here we identify and preliminarily characterize previously undescribed tRNA-derived fragments (tRF) generated from mt-TR. Northern blotting revealed distinct tRF that are differentially expressed between lung and liver and between sexes. Small RNA sequencing failed to capture these tRF unless samples were pre-treated to enzymatically remove non-canonical RNA termini and base methylation. Focusing on fragments with complete homology to mt-TR, the two most abundant tRF align uniquely to the mitochondrial genome and share conserved cleavage sites. Together, these findings uncover mitochondrial-derived tRF as a previously unrecognized small RNA metastasis modifiers and expand the functional output of the mitochondrial genome, supporting a model in which mtDNA-encoded tRF contribute to phenotype modification.
Project description:The goal of this analysis was to utilize microarray profiling to identify basal alterations in gene expression in response to TFAM depletion and mtDNA stress. Mitochondrial DNA (mtDNA) is normally present at thousands of copies per cell and is packaged into several hundred higher-order structures termed nucleoids. The abundant mtDNA-binding protein, TFAM (transcription factor A,mitochondrial), regulates nucleoid architecture, abundance and segregation. Complete mtDNA depletion profoundly impairs oxidative phosphorylation, triggering calcium-dependent stress signalling and adaptive metabolic responses. However, the cellular responses to mtDNA instability, a physiologically relevant stress observed in many human diseases and ageing, remain poorly defined. Here we show that moderate mtDNA stress elicited by TFAM deficiency engages cytosolic antiviral signalling to enhance the expression of a subset of interferon-stimulated genes. Mechanistically, we find that aberrant mtDNA packaging promotes escape of mtDNA into the cytosol, where it engages the DNA sensor cGAS (also known as MB21D1) and promotes STING (also known as TMEM173)–IRF3-dependent signalling to elevate interferon-stimulated gene expression, potentiate type I interferon responses and confer broad viral resistance. Furthermore, we demonstrate that herpesviruses induce mtDNA stress, which enhances antiviral signalling and type I interferon responses during infection. Our results further demonstrate that mitochondria are central participants in innate immunity, identify mtDNA stress as a cell-intrinsic trigger of antiviral signaling and suggest that cellular monitoring of mtDNA homeostasis cooperates with canonical virus sensing mechanisms to fully engage antiviral innate immunity. Murine embryonic fibroblasts were isolated from wild-type or Tfam+/- E13.5 littermate embryos. RNA from passage-matched wild-type and Tfam+/- MEF lines was extracted in duplicate and hybridized onto Affymetrix microarrays. Four arrays were performed in total with two technical replicates per genotype.