Project description:Modified nucleotides in tRNAs are important determinants of folding, structure and function. Here, we identify METTL8 as a mitochondrial matrix protein and active RNA methyltransferase responsible for installing m3C32 in the human mitochondrial (mt-)tRNAThr and mt-tRNASer(UCN). METTL8 crosslinks to the anticodon stem loop (ASL) of many mt-tRNAs in cells, raising the question of how methylation target specificity is achieved. Dissection of mt-tRNA recognition elements revealed U34G35 and t6A37/(ms2)i6A37, present concomitantly only in the ASLs of the two substrate mt-tRNAs, as key determinations for METTL8-mediated methylation of C32. Several lines of evidence demonstrate the influence of U34, G35, and the m3C32 and t6A37/(ms2)i6A37 modifications in mt-tRNAThr/Ser(UCN) on the structure of these mt-tRNAs. Although mt-tRNAThr/Ser(UCN) lacking METTL8-mediated m3C32 are efficiently aminoacylated and associate with mitochondrial ribosomes, mitochondrial translation is mildly impaired by lack of METTL8. Together these results define the cellular targets of METTL8 and shed new light on the role of m3C32 within mt-tRNAs.
Project description:Modified nucleotides in tRNAs are important determinants of folding, structure and function. Here, we identify METTL8 as a mitochondrial matrix protein and active RNA methyltransferase responsible for installing m3C32 in the human mitochondrial (mt-)tRNAThr and mt-tRNASer(UCN). METTL8 crosslinks to the anticodon stem loop (ASL) of many mt-tRNAs in cells, raising the question of how methylation target specificity is achieved. Dissection of mt-tRNA recognition elements revealed U34G35 and t6A37/(ms2)i6A37, present concomitantly only in the ASLs of the two substrate mt-tRNAs, as key determinations for METTL8-mediated methylation of C32. Several lines of evidence demonstrate the influence of U34, G35, and the m3C32 and t6A37/(ms2)i6A37 modifications in mt-tRNAThr/Ser(UCN) on the structure of these mt-tRNAs. Although mt-tRNAThr/Ser(UCN) lacking METTL8-mediated m3C32 are efficiently aminoacylated and associate with mitochondrial ribosomes, mitochondrial translation is mildly impaired by lack of METTL8. Together these results define the cellular targets of METTL8 and shed new light on the role of m3C32 within mt-tRNAs.
Project description:Mitochondria contain a specific translation machinery for the synthesis of respiratory chain components encoded on the mitochondrial genome. Mitochondrial tRNAs (mt-tRNAs) are also generated from the mitochondrial genome and, similar to their cytoplasmic counterparts, are modified at various positions. Here, we find that the RNA methyltransferase METTL8, is a mitochondrial protein that facilitates m3C methylation at position C32 of mt-tRNASer(UCN) and mt-tRNAThr. METTL8 knock out cells show reduced and over expressing cells enhanced respiratory chain activity. In pancreatic cancer, METTL8 levels are high, which correlates with patient survival. Indeed, METTL8 up regulation stimulates respiratory chain activity in these cells. Ribosome occupancy analysis using ribosome profiling revealed ribosome stalling on mt-tRNASer(UCN) and mt-tRNAThr codons and mass spectrometry analysis of native ribosomal subcomplexes unraveled reduced respiratory chain incorporation of the mitochondria encoded proteins ND6 and ND1. A well-balanced translation of mt-tRNASer(UCN) and mt-tRNAThr codons through METTL8-mediated C32 methylation might therefore provide optimal respiratory chain compositions and function.
Project description:Increasing evidence implicates critical roles of various epitranscriptomic RNA modifications in different biological processes. Methyltransferase METTL8 installs 3-methylcytosine modification of mitochondrial tRNAs in vitro, however, its role in intact biological systems is completely unknown. Here we show that Mettl8 is localized in the mitochondria and installs m3C in mitochondrial tRNASer(UCN)/Thr in mouse embryonic cortical neural stem cells. At molecular and cellular levels, Mettl8 deletion in cortical neural stem cells leads to reduced mitochondrial protein translation and attenuated respiration activity. At the functional level, conditional Mettl8 deletion in mice results in impaired embryonic cortical neural stem cell maintenance in vivo, which can be rescued by pharmacologically enhancing mitochondrial functions. Similarly, METTL8 regulates mitochondrial protein expression and neural stem cell maintenance in human forebrain cortical organoids. Together, our study reveals a conserved epitranscriptomic mechanism of Mettl8 and mitochondrial tRNA m3C modification in maintaining embryonic cortical neural stem cells in mice and humans.
Project description:A subset of eukaryotic tRNAs is methylated in the anticodon loop to form the 3-methylcytosine (m3C) modification. In mammals, the number of tRNAs containing m3C has expanded to include mitochondrial (mt) tRNA-Ser-UGA and mt-tRNA-Thr-UGU. Whereas the enzymes catalyzing m3C formation in nuclear-encoded cytoplasmic tRNAs have been identified, the proteins responsible for m3C modification in mt-tRNAs are unknown. Here, we show that m3C formation in human mt-tRNAs is dependent upon the Methyltransferase-Like 8 (METTL8) enzyme. We find that METTL8 is a mitochondria-associated protein that interacts with mitochondrial seryl-tRNA synthetase along with mt-tRNAs containing m3C. Human cells deficient in METTL8 exhibit loss of m3C modification in mt-tRNAs but not nuclear-encoded tRNAs. Consistent with the mitochondrial import of METTL8, the formation of m3C in METTL8-deficient cells can be rescued by re-expression of wildtype METTL8 but not by a METTL8 variant lacking the N-terminal mitochondrial localization signal. Notably, METTL8-deficiency in human cells causes alterations in the native migration pattern of mt-tRNA-Ser-UGA suggesting a role for m3C in tRNA folding. Altogether, these findings demonstrate that METTL8 is required for m3C formation in mitochondrial tRNAs and uncover a potential role for m3C modification in mitochondrial tRNA structure.
Project description:Modified nucleotides in tRNAs are important determinants of folding, structure and function. Here we identify METTL8 as a mitochondrial matrix protein and active RNA methyltransferase responsible for installing m3C32 in the human mitochondrial (mt-)tRNAThr and mt-tRNASer(UCN). METTL8 crosslinks to the anticodon stem loop (ASL) of many mt-tRNAs in cells, raising the question of how methylation target specificity is achieved. Dissection of mt-tRNA recognition elements revealed U34G35 and t6A37/(ms2)i6A37, present concomitantly only in the ASLs of the two substrate mt-tRNAs, as key determinants for METTL8-mediated methylation of C32. Several lines of evidence demonstrate the influence of U34, G35, and the m3C32 and t6A37/(ms2)i6A37 modifications in mt-tRNAThr/Ser(UCN) on the structure of these mt-tRNAs. Although mt-tRNAThr/Ser(UCN) lacking METTL8-mediated m3C32 are efficiently aminoacylated and associate with mitochondrial ribosomes, mitochondrial translation is mildly impaired by lack of METTL8. Together these results define the cellular targets of METTL8 and shed new light on the role of m3C32 within mt-tRNAs.
Project description:This project investigates the role METTL8 in human glioblastoma stem cells. In order to understand the transcriptomic changes upon deletion of METTL8, we performed this RNA seq and further downstream analyses to determine the pathways changed. From this, we hope to identify novel methods to target glioblastoma stem cells via manipulation of METTL8.