Project description:In animals the organization of the compact mitochondrial genome and lack of introns have necessitated a unique mechanism for RNA processing. To date the regulation of mitochondrial RNA processing and its importance for ribosome biogenesis and energy metabolism are not clear. To understand the in vivo role of the endoribonuclease component of the RNase P complex, MRPP3, we created conditional knockout mice. Here we show that MRPP3 is essential for life, and heart and skeletal muscle-specific knockout leads to a cardiomyopathy early in life, indicating that it is the only RNase P enzyme in mitochondria. We show that RNA processing is required for the biogenesis of the respiratory chain and mitochondrial function. Transcriptome-wide parallel analyses of RNA ends (PARE) and RNA-Seq enabled us to identify the in vivo cleavage sites of RNase P. Cleavage of the 5â² tRNA ends precedes 3â² end processing in vivo and is required for the correct biogenesis of the mitochondrial ribosomal subunits and mitoribosomal proteins that are differentially stabilized or degraded in the absence of mature rRNAs. Finally we identify that large mitoribosomal proteins can form a subcomplex on a precursor mt-RNA containing the 16S rRNA indicating that mitoribosomal biogenesis proceeds co-transcriptionally. Taken together our data show that RNA processing links transcription to translation via assembly of the mitoribosome. Total RNA was isolated from heart tissue from 11 week old control (Mrpp3loxP/loxP) and Mrpp3 knockout mice (Mrpp3loxP/loxP, +/Ckmm), TruSeq libraries produced in triplicate, sequenced and analysed for differential expression. Mitochondrial RNA was isolated from heart tissue from 11 week old control (Mrpp3loxP/loxP) and Mrpp3 knockout mice (Mrpp3loxP/loxP, +/Ckmm), PARE libraries produced in triplicate and sequenced for analysis of mitochondrial RNA processing.
Project description:Members of the mammalian AlkB family are known to mediate nucleic acid demethylation. ALKBH7, a mammalian AlkB homologue, localizes in mitochondria (mt) and affects metabolism, but its function and mechanism of action are unknown. Here, we report an approach to site-specifically detect m1A, m3C, m1G, and m22G modifications simultaneously within all cellular RNAs, and discovered that human ALKBH7 demethylates N2, N2-dimethylguanosine (m22G) and N1-methyladenosine (m1A) within mt-Ile and mt-Leu1 pre-tRNA regions, respectively, in nascent polycistronic mt-RNA. We further show that ALKBH7 regulates the processing and structural dynamics of polycistronic mt-RNAs. Depletion of ALKBH7 leads to increased polycistronic mt-RNA processing, reduced steady-state mitochondria-encoded tRNA levels and protein translation, as well as notably decreased mitochondrial activity. Thus, we identify ALKBH7 as an RNA demethylase that controls nascent mt-RNA processing and mitochondrial activity.
Project description:The expression of mitochondrially-encoded genes requires the efficient processing of long precursor RNAs at the 5´ and 3´ ends of tRNAs, a process which, when disrupted, results in disease. Two such mutations reside within mt-tRNALeu(UUR); a m.3243A>G transition, which is the most common cause of MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes), and m.3302A>G which often causes mitochondrial myopathy (MM). We used parallel analysis of RNA ends (PARE) that captures the 5´ terminal end of 5´-monophosphorylated mitochondrial RNAs to compare the effects of the m.3243A>G and m.3302A>G mutations on mitochondrial tRNA processing. We confirmed previously identified RNA processing defects, identified common internal cleavage sites and new sites unique to the m.3243A>G mutants that do not correspond to transcript ends. These sites occur in regions of predicted RNA secondary structure, or are in close proximity to such regions, and may identify regions of importance to the processing of mtRNAs.
Project description:In animals the organization of the compact mitochondrial genome and lack of introns have necessitated a unique mechanism for RNA processing. To date the regulation of mitochondrial RNA processing and its importance for ribosome biogenesis and energy metabolism are not clear. To understand the in vivo role of the endoribonuclease component of the RNase P complex, MRPP3, we created conditional knockout mice. Here we show that MRPP3 is essential for life, and heart and skeletal muscle-specific knockout leads to a cardiomyopathy early in life, indicating that it is the only RNase P enzyme in mitochondria. We show that RNA processing is required for the biogenesis of the respiratory chain and mitochondrial function. Transcriptome-wide parallel analyses of RNA ends (PARE) and RNA-Seq enabled us to identify the in vivo cleavage sites of RNase P. Cleavage of the 5′ tRNA ends precedes 3′ end processing in vivo and is required for the correct biogenesis of the mitochondrial ribosomal subunits and mitoribosomal proteins that are differentially stabilized or degraded in the absence of mature rRNAs. Finally we identify that large mitoribosomal proteins can form a subcomplex on a precursor mt-RNA containing the 16S rRNA indicating that mitoribosomal biogenesis proceeds co-transcriptionally. Taken together our data show that RNA processing links transcription to translation via assembly of the mitoribosome.
Project description:We investigated the changes in the abundance of reads across the entire mitochondrial transcriptome, we found an increase in the regions that span gene boundaries, where RNA processing is required to release individual mitochondrial RNAs from the precursor transcripts. These data confirm an impairment of mt-tRNA processing efficiency without severe effects on mature mt-mRNA or mt-tRNA steady-state levels. Strand-specific coverage profiles were generated in bedGraph format and normalised to library size (RPM; reads per million mapped).
Project description:Mitochondrial biogenesis relies on both the nuclear and the mitochondrial genomes, and the mechanisms that support their coordinated expression are not fully understood. Improper mitochondrial DNA expression can lead to inborn error of metabolism, inflammation, and aging. Here, we investigate N6AMT1, a nucleo-cytosolic multi-substrate methyltransferase. We analyze genetic dependency, transcription, translation, and proteomic profiles of N6AMT1-depleted cells and report that N6AMT1 is necessary for the cytosolic translation of factors involved in mitochondrial RNA metabolism, including subunits of the mitochondrial RNase P. In the absence of N6AMT1, RNA processing and translation within mitochondria are impaired, while double-stranded RNA accumulates in mitochondrial RNA granules causing an interferon response. Our work highlights a cytosolic program required for proper mitochondrial biogenesis, with consequences on innate immunity.
Project description:Mitochondrial biogenesis relies on both the nuclear and mitochondrial genomes, and imbalance in their expression can lead to inborn errors of metabolism, inflammation, and aging. Here, we investigate N6AMT1, a nucleo-cytosolic methyltransferase that exhibits genetic codependency with mitochondria. We determine transcriptional and translational profiles of N6AMT1 and report that it is required for the cytosolic translation of TRMT10C (MRPP1) and PRORP (MRPP3), two subunits of the mitochondrial RNAse P enzyme. In the absence of N6AMT1, or when its catalytic activity is abolished, RNA processing within mitochondria is impaired, leading to the accumulation of unprocessed and double-stranded RNA, thus preventing mitochondrial protein synthesis and oxidative phosphorylation, and leading to an immune response. Our work sheds light on the function of N6AMT1 in protein synthesis and highlights a cytosolic program required for proper mitochondrial biogenesis.
Project description:The mitochondrial matrix is unique in that it must integrate folding and assembly of proteins derived from nuclear and mitochondrial genomes. In C. elegans, the mitochondrial unfolded protein response (UPRmt) senses matrix protein misfolding and induces a program of nuclear gene expression, including mitochondrial chaperonins, to promote mitochondrial proteostasis. While misfolded mitochondrial matrix-localized ornithine trans-carbamylase (OTC) induces chaperonin expression, our understanding of mammalian UPRmt is rudimentary, reflecting a lack of acute triggers for UPRmt activation. This limitation has prevented analysis of the cellular responses to matrix protein misfolding and the effects of UPRmt on mitochondrial translation to control protein folding loads. Here, we combine pharmacological inhibitors of matrix-localized HSP90/TRAP1 or LON protease, which promote chaperonin expression, with global transcriptional and proteomic analysis to reveal an extensive and acute response of human cells to UPRmt. This response involved widespread induction of nuclear genes, including matrix-localized proteins involved in folding, pre-RNA processing and translation. Functional studies revealed rapid but reversible translation inhibition in mitochondria occurring concurrently with defects in pre-RNA processing due to transcriptional repression and LON-dependent turnover of the mitochondrial pre-RNA processing nuclease MRPP3. This study reveals that acute mitochondrial protein folding stress activates both increased chaperone availability within the matrix and reduced matrix-localized protein synthesis through translational inhibition, and provides a framework for further dissection of mammalian UPRmt. triplicate experiment of 3 conditions (untreated, GTPP treatment, CDDO treatment)