Technical knockout, a Drosophila model of mitochondrial deafness.
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ABSTRACT:
SUBMITTER: Toivonen JM
PROVIDER: S-EPMC1461776 | biostudies-other | 2001 Sep
REPOSITORIES: biostudies-other
Publications
Technical knockout, a Drosophila model of mitochondrial deafness.
Toivonen J M JM O'Dell K M KM Petit N N Irvine S C SC Knight G K GK Lehtonen M M Longmuir M M Luoto K K Touraille S S Wang Z Z Alziari S S Shah Z H ZH Jacobs H T HT
Genetics 20010901 1
Mutations in mtDNA-encoded components of the mitochondrial translational apparatus are associated with diverse pathological states in humans, notably sensorineural deafness. To develop animal models of such disorders, we have manipulated the nuclear gene for mitochondrial ribosomal protein S12 in Drosophila (technical knockout, tko). The prototypic mutant tko(25t) exhibits developmental delay, bang sensitivity, impaired male courtship, and defective response to sound. On the basis of a transgeni ...[more]
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Project description:RNase Z(L) is a highly conserved tRNA 3'-end processing endoribonuclease. Similar to its mammalian counterpart, Drosophila RNase Z(L) (dRNaseZ) has a mitochondria targeting signal (MTS) flanked by two methionines at the N-terminus. Alternative translation initiation yields two protein forms: the long one is mitochondrial, and the short one may localize in the nucleus or cytosol. Here, we have generated a mitochondria specific knockout of the dRNaseZ gene. In this in vivo model, cells deprived of dRNaseZ activity display impaired mitochondrial polycistronic transcript processing, increased reactive oxygen species (ROS) and a switch to aerobic glycolysis compensating for cellular ATP. Damaged mitochondria impose a cell cycle delay at the G2 phase disrupting cell proliferation without affecting cell viability. Antioxidants attenuate genotoxic stress and rescue cell proliferation, implying a critical role for ROS. We suggest that under a low-stress condition, ROS activate tumor suppressor p53, which modulates cell cycle progression and promotes cell survival. Transcriptional profiling of p53 targets confirms upregulation of antioxidant and cycB-Cdk1 inhibitor genes without induction of apoptotic genes. This study implicates Drosophila RNase Z(L) in a novel retrograde signaling pathway initiated by the damage in mitochondria and manifested in a cell cycle delay before the mitotic entry.
| S-EPMC4666369 | biostudies-literature
Project description:Background: A point mutation in the Drosophila gene technical knockout (tko), encoding mitoribosomal protein S12, provokes a phenotype of respiratory chain deficiency, developmental delay and neurological abnormalities similar to those presented in many human mitochondrial disorders, as well as defective courtship behaviour. Results: Transcriptome-wide analysis of gene expression in tko25t mutant flies revealed systematic, compensatory changes in expression of genes connected with metabolism, including upregulation of lactate dehydrogenase and of many genes involved in the catabolism of fats and proteins, the TCA cycle and anaplerotic pathways feeding into it. Gut-specific enzymes involved in the primary mobilization of dietary fat and protein, as well as a number of transport functions, were strongly upregulated, consistent with the idea that OXPHOS dysfunction is perceived physiologically as a starvation for particular biomolecules. Many stress-response genes were also induced. Other changes may reflect a signature of developmental delay. There was also down-regulation of genes connected with reproduction, including gametogenesis, especially in females, and courtship behaviour in males. This might represent a programmed response to a mitochondrially generated starvation signal. Although human sexual behaviour is not known to respond to mitochondrial dysfunction, the underlying signaling pathway, if conserved, could influence many physiological processes in response to nutritional stress. Transcriptomic analysis suggested the possible involvement of the Akt1/sgg signaling pathway(s). Conclusions: The transformation of metabolism in response to mitochondrial dysfunction, including digestive and absorptive functions, gives important clues as to how novel therapeutic strategies for mitochondrial disorders might be developed. Experiment Overall Design: Crosses and maintenance: Inbreeding under stressful conditions inevitably results in the selection of compensatory alleles of many genes. In order to avoid such issues, and thus determine the global effects on gene expression of the tko25t mutation in a truly unselected and 'wild-type' background, we outbred tko25t over more than 10 generations by back-crossing to each of two commonly used wild-type strains, Canton S and Oregon R. Subsequent to this backcrossing, tko25t was maintained in each background using a balancer chromosome. These stocks were then used to generate a tko25t mutant F1 generation, by crossing virgin Canton S tko25t homozygous mutant females with Oregon R tko25t males. For comparison, we generated otherwise isogenic wild-type F1 progeny by crossing virgin Canton S wild-type females with Oregon R wild-type males. Experiment Overall Design: Samples: Both tko25t and wild-type Drosophila adult flies of both sexes were collected and aged to 1 day old prior to RNA extraction and hybridization on Affymetrix microarrays. We extracted RNA from 3 independent such crosses. Experiment Overall Design: Comparative analysis: Data analysis for each gene in the array compared each tko25t mutant RNA isolate with each wild-type RNA isolate from flies of the given sex, generating 9 comparative measurements, over which the statistical analysis was performed.
2010-01-19 | E-GEOD-10169 | biostudies-arrayexpress
Project description:BACKGROUND: A point mutation in the Drosophila gene technical knockout (tko), encoding mitoribosomal protein S12, was previously shown to cause a phenotype of respiratory chain deficiency, developmental delay, and neurological abnormalities similar to those presented in many human mitochondrial disorders, as well as defective courtship behavior. METHODOLOGY/PRINCIPAL FINDINGS: Here, we describe a transcriptome-wide analysis of gene expression in tko(25t) mutant flies that revealed systematic and compensatory changes in the expression of genes connected with metabolism, including up-regulation of lactate dehydrogenase and of many genes involved in the catabolism of fats and proteins, and various anaplerotic pathways. Gut-specific enzymes involved in the primary mobilization of dietary fats and proteins, as well as a number of transport functions, were also strongly up-regulated, consistent with the idea that oxidative phosphorylation OXPHOS dysfunction is perceived physiologically as a starvation for particular biomolecules. In addition, many stress-response genes were induced. Other changes may reflect a signature of developmental delay, notably a down-regulation of genes connected with reproduction, including gametogenesis, as well as courtship behavior in males; logically this represents a programmed response to a mitochondrially generated starvation signal. The underlying signalling pathway, if conserved, could influence many physiological processes in response to nutritional stress, although any such pathway involved remains unidentified. CONCLUSIONS/SIGNIFICANCE: These studies indicate that general and organ-specific metabolism is transformed in response to mitochondrial dysfunction, including digestive and absorptive functions, and give important clues as to how novel therapeutic strategies for mitochondrial disorders might be developed.
| S-EPMC2798955 | biostudies-literature
Project description:BackgroundMice carrying targeted mutations are important for investigating gene function and the role of genes in disease, but off-target mutagenic effects associated with the processes of generating targeted alleles, for instance using Crispr, and culturing embryonic stem cells, offer opportunities for spontaneous mutations to arise. Identifying spontaneous mutations relies on the detection of phenotypes segregating independently of targeted alleles, and having a broad estimate of the level of mutations generated by intensive breeding programmes is difficult given that many phenotypes are easy to miss if not specifically looked for. Here we present data from a large, targeted knockout programme in which mice were analysed through a phenotyping pipeline. Such spontaneous mutations segregating within mutant lines may confound phenotypic analyses, highlighting the importance of record-keeping and maintaining correct pedigrees.ResultsTwenty-five lines out of 1311 displayed different deafness phenotypes that did not segregate with the targeted allele. We observed a variety of phenotypes by Auditory Brainstem Response (ABR) and behavioural assessment and isolated eight lines showing early-onset severe progressive hearing loss, later-onset progressive hearing loss, low frequency hearing loss, or complete deafness, with vestibular dysfunction. The causative mutations identified include deletions, insertions, and point mutations, some of which involve new genes not previously associated with deafness while others are new alleles of genes known to underlie hearing loss. Two of the latter show a phenotype much reduced in severity compared to other mutant alleles of the same gene. We investigated the ES cells from which these lines were derived and determined that only one of the 8 mutations could have arisen in the ES cell, and in that case, only after targeting. Instead, most of the non-segregating mutations appear to have occurred during breeding of mutant mice. In one case, the mutation arose within the wildtype colony used for expanding mutant lines.ConclusionsOur data show that spontaneous mutations with observable effects on phenotype are a common side effect of intensive breeding programmes, including those underlying targeted mutation programmes. Such spontaneous mutations segregating within mutant lines may confound phenotypic analyses, highlighting the importance of record-keeping and maintaining correct pedigrees.
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Project description:A point mutation in the Drosophila gene that codes for the major adult isoform of adenine nuclear translocase (ANT) represents a model for human diseases that are associated with ANT insufficiency [stress-sensitive B(1) (sesB(1))]. We characterized the organismal, bioenergetic and molecular phenotype of sesB(1) flies then tested strategies to compensate the mutant phenotype. In addition to developmental delay and mechanical-stress-induced seizures, sesB(1) flies have an impaired response to sound, defective male courtship, female sterility and curtailed lifespan. These phenotypes, excluding the latter two, are shared with the mitoribosomal protein S12 mutant, tko(25t). Mitochondria from sesB(1) adults showed a decreased respiratory control ratio and downregulation of cytochrome oxidase. sesB(1) adults exhibited ATP depletion, lactate accumulation and changes in gene expression that were consistent with a metabolic shift towards glycolysis, characterized by activation of lactate dehydrogenase and anaplerotic pathways. Females also showed downregulation of many genes that are required for oogenesis, and their eggs, although fertilized, failed to develop to the larval stages. The sesB(1) phenotypes of developmental delay and mechanical-stress-induced seizures were alleviated by an altered mitochondrial DNA background. Female sterility was substantially rescued by somatic expression of alternative oxidase (AOX) from the sea squirt Ciona intestinalis, whereas AOX did not alleviate developmental delay. Our findings illustrate the potential of different therapeutic strategies for ANT-linked diseases, based on alleviating metabolic stress.
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Project description:Pediatric mitochondrial disorders are a devastating category of diseases caused by deficiencies in mitochondrial function. Leigh Syndrome (LS) is the most common of these diseases with symptoms typically appearing within the first year of birth and progressing rapidly until death, usually by 6-7 years of age. Our lab has recently shown that genetic inhibition of the mechanistic target of rapamycin (TOR) rescues the short lifespan of yeast mutants with defective mitochondrial function, and that pharmacological inhibition of TOR by administration of rapamycin significantly rescues the shortened lifespan, neurological symptoms, and neurodegeneration in a mouse model of LS. However, the mechanism by which TOR inhibition exerts these effects, and the extent to which these effects can extend to other models of mitochondrial deficiency, are unknown. Here, we probe the effects of TOR inhibition in a Drosophila model of complex I deficiency. Treatment with rapamycin robustly suppresses the lifespan defect in this model of LS, without affecting behavioral phenotypes. Interestingly, this increased lifespan in response to TOR inhibition occurs in an autophagy-independent manner. Further, we identify a fat storage defect in the ND2 mutant flies that is rescued by rapamycin, supporting a model that rapamycin exerts its effects on mitochondrial disease in these animals by altering metabolism.
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Project description:Lysine methylation is a reversible post-translational modification that affects protein function. Lysine methylation is involved in regulating the function of both histone and non-histone proteins, thereby influencing both cellular transcription and the activation of signaling pathways. To date, only a few lysine methyltransferases have been studied in depth. Here, we study the Drosophila homolog of the human lysine methyltransferase SETD3, CG32732/dSETD3. Since mammalian SETD3 is involved in cell proliferation, we tested the effect of dSETD3 on proliferation and growth of Drosophila S2 cells and whole flies. Knockdown of dSETD3 did not alter mTORC1 activity nor proliferation rate of S2 cells. Complete knock-out of dSETD3 in Drosophila flies did not affect their weight, growth rate or fertility. dSETD3 KO flies showed normal responses to starvation and hypoxia. In sum, we could not identify any clear phenotypes for SETD3 knockout animals, indicating that additional work will be required to elucidate the molecular and physiological function of this highly conserved enzyme.
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Project description:Mitochondrial dysfunction causes poorly understood tissue-specific pathology stemming from primary defects in respiration, coupled with altered reactive oxygen species (ROS), metabolic signaling, and apoptosis. The A1555G mtDNA mutation that causes maternally inherited deafness disrupts mitochondrial ribosome function, in part, via increased methylation of the mitochondrial 12S rRNA by the methyltransferase mtTFB1. In patient-derived A1555G cells, we show that 12S rRNA hypermethylation causes ROS-dependent activation of AMP kinase and the proapoptotic nuclear transcription factor E2F1. This retrograde mitochondrial-stress relay is operative in vivo, as transgenic-mtTFB1 mice exhibit enhanced 12S rRNA methylation in multiple tissues, increased E2F1 and apoptosis in the stria vascularis and spiral ganglion neurons of the inner ear, and progressive E2F1-dependent hearing loss. This mouse mitochondrial disease model provides a robust platform for deciphering the complex tissue specificity of human mitochondrial-based disorders, as well as the precise pathogenic mechanism of maternally inherited deafness and its exacerbation by environmental factors.
| S-EPMC3285425 | biostudies-literature
Project description:Despite the fact that important genetic diseases are caused by mutant mitochondrial ribosomes, the molecular mechanisms by which such ribosomes result in a clinical phenotype remain largely unknown. The absence of experimental models for mitochondrial diseases has also prevented the rational search for therapeutic interventions. Here, we report on the construction of bacterial hybrid ribosomes that contain various versions of the mitochondrial decoding region of ribosomal RNA. We show that the pathogenic mutations A1555G and C1494T decrease the accuracy of translation and render the ribosomal decoding site hypersusceptible to aminoglycoside antibiotics. This finding suggests misreading of the genetic code as an important molecular mechanism in disease pathogenesis.
| S-EPMC2265171 | biostudies-literature
Project description:Background: A point mutation in the Drosophila gene technical knockout (tko), encoding mitoribosomal protein S12, provokes a phenotype of respiratory chain deficiency, developmental delay and neurological abnormalities similar to those presented in many human mitochondrial disorders, as well as defective courtship behaviour. Results: Transcriptome-wide analysis of gene expression in tko25t mutant flies revealed systematic, compensatory changes in expression of genes connected with metabolism, including upregulation of lactate dehydrogenase and of many genes involved in the catabolism of fats and proteins, the TCA cycle and anaplerotic pathways feeding into it. Gut-specific enzymes involved in the primary mobilization of dietary fat and protein, as well as a number of transport functions, were strongly upregulated, consistent with the idea that OXPHOS dysfunction is perceived physiologically as a starvation for particular biomolecules. Many stress-response genes were also induced. Other changes may reflect a signature of developmental delay. There was also down-regulation of genes connected with reproduction, including gametogenesis, especially in females, and courtship behaviour in males. This might represent a programmed response to a mitochondrially generated starvation signal. Although human sexual behaviour is not known to respond to mitochondrial dysfunction, the underlying signaling pathway, if conserved, could influence many physiological processes in response to nutritional stress. Transcriptomic analysis suggested the possible involvement of the Akt1/sgg signaling pathway(s). Conclusions: The transformation of metabolism in response to mitochondrial dysfunction, including digestive and absorptive functions, gives important clues as to how novel therapeutic strategies for mitochondrial disorders might be developed. Keywords: mutant analysis
2010-01-12 | GSE10169 | GEO