Project description:Argonaute-2 forms together with associated miRNAs the RNA induced silencing complex (RISC), which recognizes target mRNAs for translational silencing and degradation. Here, we identified thirteen heterozygous mutations in AGO2 in a cohort of 20 patients affected by mild to severe neurodevelopmental disorder. Each of the identified single amino acid mutations results in impaired shRNA-mediated silencing. Through biochemical and molecular dynamic analyses, we uncovered two mutation-specific functional consequences: one mutation (p.G733R) induces a loss-of-function, whereas the other exchanges lead to increased binding of AGO2 to mRNA targets. The latter is supported by decreased phosphorylation of a C-terminal cluster of serine residues known to be involved in mRNA target release, and by the increased formation of dendritic P-bodies in neurons. Our data highlight the complexity underlying AGO2 function, and underline the importance of tight gene expression regulation through the dynamic AGO2-RNA association for neuronal development.
Project description:The reduced sperm count observed in Ago2 cKO mice implies that AGO2 has non-redundant functions in the male germ line. Because AGO2 is a key protein in the RNA interference (RNAi) pathway, we first postulated that AGO2 loss disrupts normal transcriptional and translational dynamics of target mRNAs relevant to sperm maturation. To address this hypothesis, we took advantage of the apparently normal spermatogenesis in Ago2 cKO mice, which allowed us to purify matched meiotic and post-meiotic germ cells from Ago2 cKO and wild type controls. We examined changes in the transcriptome and proteome of these two spermatogenic stages in Ago2 cKO relative to control mice using RNA-seq and quantitative mass spectrometry (MS). To further examine if the changes in mRNA and protein levels detected in Ago2 cKO germ cells was due to a loss of regulation by the canonical AGO2-miRNA pathway, we characterized AGO2 protein interactors by AGO2 immunoprecipitation-mass spectrometry (IP-MS) in cytoplasmic and nuclear fractions of post-meiotic cells
Project description:We elucidate a neurological syndrome affecting both the PNS and CNS defined by CLP1 mutations that impair tRNA splicing Identification and biochemical characterization of mutant CLP1 in human patients
Project description:In mammals, RNA interference (RNAi) was historically studied as a cytoplasmic event, however, in the last decade growing number of reports convincingly show nuclear localization of the AGO proteins. Nevertheless, the mechanism and the extent of nuclear RNAi remains to be fully elucidated. We found that reduced Lamin A levels significantly induced nuclear influx of AGO2 in SHSY5Y neuroblastoma and A375 melanoma cancer cell lines, which normally have no nuclear AGO2. Lamin A KO manifested a more pronounced effect in SHSY5Y cells compared to A375 evident by changes in cell morphology, increased cell proliferation and oncogenic miRNA expression. Furthermore, in SHSY5Y cells, AGO fPAR-CLIP in Lamin A KO cells revealed significantly reduced activity of RNAi. Further exploration of the nuclear AGO interactome by mass spectrometry indicated that AGO2 is in complex with FAM120A, an RNA binding protein and known interactor of AGO2. By performing FAM120A fPAR-CLIP we discovered that FAM120A co-binds AGO targets and that this competition reduces the activity of RNAi. Therefore, loss of Lamin A triggers nuclear AGO2 translocation, RNAi impairment and selective upregulation of oncogenic miRNAs to facilitate cancer cell proliferation.
Project description:In mammals, RNA interference (RNAi) was historically studied as a cytoplasmic event, however, in the last decade growing number of reports convincingly show nuclear localization of the AGO proteins. Nevertheless, the mechanism and the extent of nuclear RNAi remains to be fully elucidated. We found that reduced Lamin A levels significantly induced nuclear influx of AGO2 in SHSY5Y neuroblastoma and A375 melanoma cancer cell lines, which normally have no nuclear AGO2. Lamin A KO manifested a more pronounced effect in SHSY5Y cells compared to A375 evident by changes in cell morphology, increased cell proliferation and oncogenic miRNA expression. Furthermore, in SHSY5Y cells, AGO fPAR-CLIP in Lamin A KO cells revealed significantly reduced activity of RNAi. Further exploration of the nuclear AGO interactome by mass spectrometry indicated that AGO2 is in complex with FAM120A, an RNA binding protein and known interactor of AGO2. By performing FAM120A fPAR-CLIP we discovered that FAM120A co-binds AGO targets and that this competition reduces the activity of RNAi. Therefore, loss of Lamin A triggers nuclear AGO2 translocation, RNAi impairment and selective upregulation of oncogenic miRNAs to facilitate cancer cell proliferation.
Project description:Mutations in either the mitochondrial or nuclear genomes are associated with a diverse group of human disorders characterized by impaired mitochondrial respiration. Within this group, an increasing number of mutations have been identified in nuclear genes involved in mitochondrial RNA biology. The TEFM gene codes for the mitochondrial transcription elongation factor responsible for enhancing the processivity of mitochondrial RNA polymerase, POLRMT. Here, we report for the first time that TEFM variants are associated with mitochondrial respiratory chain deficiency and a wide range of clinical presentations including neonatal lactic acidosis, epileptic encephalopathy, developmental delay, intellectual disability or mitochondrial myopathy with a treatable neuromuscular transmission defect. Mechanistically, we show that muscle samples and primary fibroblasts from the affected individuals have reduced levels of promoter distal mitochondrial RNA transcripts, consistent with decreased processivity of POLRMT when TEFM is dysfunctional. We provide further evidence for the pathogenicity of these variants by investigating mitochondrial transcription and proteomic changes in patient cells and muscle and by studying TEFM activity in an in vitro system. Finally, tefm knock-down in zebrafish embryos resulted in neuromuscular junction abnormalities and abnormal mitochondrial function, strengthening the genotype-phenotype correlation. In conclusion, our study highlights that TEFM regulates mitochondrial transcription elongation in human tissues and its defect results in variable, tissue specific neurological and neuromuscular symptoms.