Functional Analysis of the PCCA and PCCB Gene Variants Predicted to Affect Splicing.
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ABSTRACT:
SUBMITTER: Bychkov I
PROVIDER: S-EPMC8073151 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:BACKGROUND:Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Over 1800 CFTR mutations have been reported, and about 12% of mutations are believed to impair pre-mRNA splicing. Given that several synthetic, non-splice-junction synonymous substitutions have been reported to alter splicing in CFTR, we predicted that naturally occurring synonymous substitutions may be erroneously classified as functionally neutral. METHODS:Computational tools were used to predict the effect of synonymous substitutions on CFTR pre-mRNA splicing. The functional consequences of selected substitutions were evaluated using a minigene splicing assay. RESULTS:Two synonymous mutations were shown to have a dramatic effect on CFTR pre-mRNA splicing, and consequently could alter protein integrity and phenotypic outcome. CONCLUSIONS:Traditional methods of mutation analysis overlook splicing defects that occur at internal positions in coding exons, especially synonymous substitutions. We show that bioinformatics tools and minigene splicing assays are a potent combination to prioritize and identify mutations that cause aberrant CFTR pre-mRNA splicing.
| S-EPMC3440543 | biostudies-literature
Project description:BACKGROUND:Propionic acidemia (PA) is an autosomal recessive metabolic disorder caused by the deficiency of the mitochondrial protein propionyl-CoA carboxylase (PCC) and is associated with pathogenic variants in either of the two genes PCCA or PCCB. The present study aimed to identify the genetic cause of three Chinese patients with PA. CASE PRESENTATION:Three Chinese PA patients were diagnosed by using gas chromatography-mass spectrometry(GC-MS), tandem mass spectrometry (MS/MS) and molecular diagnostic methods. All patients had onset in the neonatal period. One patient died of infection and metabolic decompensation, and the other two had mild to moderate developmental delay/mental retardation. Mutation analysis of the PCCA gene identified that patient 1 carried the compound heterozygous c.1288C > T(p.R430X) and c.2002G > A(p.G668R), and patient 2 was homozygous for the c.1426C > T(p.R476X) mutation. Mutation analysis of the PCCB gene identified that patient 3 harbored the compound heterozygous mutations c.359_360del AT(p.Y120Cfs*40) and c.1398 + 1G > A. Among these mutations, three (c.1288C > T, c.359_360del AT and c.1398 + 1G > A) are novel. CONCLUSIONS:We reported three Chinese PA patients who had PCCA or PCCB mutants. Among them, in the PCCA gene, c.1288C > T(p.R430X) was a nonsense mutation, resulting in a truncated protein. c.359_360del AT was a frameshift mutation, leading to a p.Y120Cfs*40 change in the amino acid sequence in the PCCB protein. c.1398 + 1G > A was a splicing mutation, causing skipping of the exons 13-14. In conclusion, the novel mutations uncovered in this study will expands the mutation spectrum of PA.
| S-EPMC7137301 | biostudies-literature
Project description:Propionic acidemia (PA) is a classical inborn error of metabolism with high morbidity that results from the inability of the propionyl-CoA carboxylase (PCC) enzyme to convert propionyl-CoA to methylmalonyl-CoA. PA is inherited in an autosomal recessive fashion due to functional loss of both alleles of either PCCA or PCCB. These genes are highly conserved across evolutionarily diverse species and share extensive similarity with pcca-1 and pccb-1 in the nematode, Caenorhabditis elegans. Here, we report the global metabolic effects of deletion in a single PCC gene, either pcca-1 or pccb-1, in C. elegans. Animal lifespan was significantly reduced relative to wild-type worms in both mutant strains, although to a greater degree in pcca-1. Mitochondrial oxidative phosphorylation (OXPHOS) capacity and efficiency as determined by direct polarography of isolated mitochondria were also significantly reduced in both mutant strains. While in vivo quantitation of mitochondrial physiology was normal in pccb-1 mutants, pcca-1 deletion mutants had significantly increased mitochondrial matrix oxidant burden as well as significantly decreased mitochondrial membrane potential and mitochondrial content. Whole worm steady-state free amino acid profiling by UPLC revealed reduced levels in both mutant strains of the glutathione precursor cysteine, possibly suggestive of increased oxidative stress. Intermediary metabolic flux analysis by GC/MS with 1,6-13C2-glucose further showed both PCC deletion strains had decreased accumulation of a distal tricarboxylic acid (TCA) cycle metabolic intermediate (+1 malate), isotopic enrichment in a proximal TCA cycle intermediate (+1 citrate), and increased +1 lactate accumulation. GC/MS analysis further revealed accumulation in the PCC mutants of a small amount of 3-hydroxypropionate, which appeared to be metabolized in C. elegans to oxalate through a unique metabolic pathway. Collectively, these detailed metabolic investigations in translational PA model animals with genetic-based PCC deficiency reveal their significantly dysregulated energy metabolism at multiple levels, including reduced mitochondrial OXPHOS capacity, increased oxidative stress, and inhibition of distal TCA cycle flux, culminating in reduced animal lifespan. These findings demonstrate that the pathophysiology of PA extends well beyond what has classically been understood as a single PCC enzyme deficiency with toxic precursor accumulation, and suggest that therapeutically targeting the globally disrupted energy metabolism may offer novel treatment opportunities for PA.SummaryTwo C. elegans model animals of propionic acidemia with single-gene pcca-1 or pccb-1 deletions have reduced lifespan with significantly reduced mitochondrial energy metabolism and increased oxidative stress, reflecting the disease's broader pathophysiology beyond a single enzyme deficiency with toxic precursor accumulation.
| S-EPMC5832583 | biostudies-literature
Project description:BackgroundIn recent years, the elucidation of splicing abnormalities as a cause of hereditary diseases has progressed. However, there are no comprehensive reports of suspected splicing variants in the CLCN5 gene in Dent disease cases. We reproduced gene mutations by mutagenesis, inserted the mutated genes into minigene vectors, and investigated the pathogenicity and onset mechanisms of these variants.MethodsWe conducted functional splicing assays using a hybrid minigene for six suspected splicing variants (c.105G>A, c.105+5G>C, c.106-17T>G, c.393+4A>G, c.517-8A>G, c.517-3C>A) in CLCN5. We extracted information on these variants from the Human Gene Mutation Database. We reproduced minigene vectors with the insertion of relevant exons with suspected splicing variants. We then transfected these minigene vectors into cultured cells and extracted and analyzed the mRNA. In addition, we conducted in silico analysis to confirm our minigene assay results.ResultsWe successfully determined that five of these six variants are pathogenic via the production of splicing abnormalities. One showed only normal transcript production and was thus suspected of not being pathogenic (c.106-17T>G).ConclusionWe found that five CLCN5 variants disrupted the original splice site, resulting in aberrant splicing. It is sometimes difficult to obtain mRNA from patient samples because of the fragility of mRNA or its low expression level in peripheral leukocytes. Our in vitro system can be used as an alternative to in vivo assays to determine the pathogenicity of suspected splicing variants.
| S-EPMC7935734 | biostudies-literature
Project description:Mutational screening of the breast cancer susceptibility gene BRCA1 leads to the identification of numerous pathogenic variants such as frameshift and nonsense variants, as well as large genomic rearrangements. The screening moreover identifies a large number of variants, for example, missense, silent, and intron variants, which are classified as variants of unknown clinical significance owing to the lack of causal evidence. Variants of unknown clinical significance can potentially have an impact on splicing and therefore functional examinations are warranted to classify whether these variants are pathogenic or benign. Here we validate a mini-gene splicing assay by comparing the results of 24 variants with previously published data from RT-PCR analysis on RNA from blood samples/lymphoblastoid cell lines. The analysis showed an overall concordance of 100%. In addition, we investigated 13 BRCA1 variants of unknown clinical significance or putative variants affecting splicing by in silico analysis and mini-gene splicing assay. Both the in silico analysis and mini-gene splicing assay classified six BRCA1 variants as pathogenic (c.80+1G>A, c.132C>T (p.=), c.213-1G>A, c.670+1delG, c.4185+1G>A, and c.5075-1G>C), whereas six BRCA1 variants were classified as neutral (c.-19-22_-19-21dupAT, c.302-15C>G, c.547+14delG, c.4676-20A>G, c.4987-21G>T, and c.5278-14C>G) and one BRCA1 variant remained unclassified (c.670+16G>A). In conclusion, our study emphasizes that in silico analysis and mini-gene splicing assays are important for the classification of variants, especially if no RNA is available from the patient. This knowledge is crucial for proper genetic counseling of patients and their family members.
| S-EPMC4231409 | biostudies-literature
Project description:INTRODUCTION: The underlying pathogenic mechanism of a large fraction of DNA variants of disease-causing genes is the disruption of the splicing process. We aimed to investigate the effect on splicing of the BRCA2 variants c.8488-1G > A (exon 20) and c.9026_9030del (exon 23), as well as 41 BRCA2 variants reported in the Breast Cancer Information Core (BIC) mutation database. METHODS: DNA variants were analyzed with the splicing prediction programs NNSPLICE and Human Splicing Finder. Functional analyses of candidate variants were performed by lymphocyte RT-PCR and/or hybrid minigene assays. Forty-one BIC variants of exons 19, 20, 23 and 24 were bioinformatically selected and generated by PCR-mutagenesis of the wild type minigenes. RESULTS: Lymphocyte RT-PCR of c.8488-1G > A showed intron 19 retention and a 12-nucleotide deletion in exon 20, whereas c.9026_9030del did not show any splicing anomaly. Minigene analysis of c.8488-1G > A displayed the aforementioned aberrant isoforms but also exon 20 skipping. We further evaluated the splicing outcomes of 41 variants of four BRCA2 exons by minigene analysis. Eighteen variants presented splicing aberrations. Most variants (78.9%) disrupted the natural splice sites, whereas four altered putative enhancers/silencers and had a weak effect. Fluorescent RT-PCR of minigenes accurately detected 14 RNA isoforms generated by cryptic site usage, exon skipping and intron retention events. Fourteen variants showed total splicing disruptions and were predicted to truncate or eliminate essential domains of BRCA2. CONCLUSIONS: A relevant proportion of BRCA2 variants are correlated with splicing disruptions, indicating that RNA analysis is a valuable tool to assess the pathogenicity of a particular DNA change. The minigene system is a straightforward and robust approach to detect variants with an impact on splicing and contributes to a better knowledge of this gene expression step.
| S-EPMC3446350 | biostudies-literature
Project description:ObjectiveArgininosuccinate lyase (ASL) gene mutations account for argininosuccinic aciduria (ASA). This study aimed to design a minigene construct of ASL gene in order to investigate the impact of variants on splicing.MethodsThe peripheral blood samples were collected from the family members, and genomic DNA was extracted for gene diagnosis using the total exon sequencing method. The novel mutation gene was cloned into pEGFP-C1 vector, and the pathogenicity of the mutation was examined in cultured cells in vitro.ResultsThe clinical diagnosis of the proband as ASA was clear. Two pathogenic mutations, c.281G>T (p.Arg94Leu) and c.208-15 T>A were detected in the ASL gene, and the two mutations had not been reported. The minigene expression in vitro confirmed that c.208-15 T>A could cause aberrant splicing, resulting in the retention of 13 bp in intron 2 to exon 3.ConclusionTwo new pathogenic mutations of ASL gene, c.208-15 T>A and c.281G>T, were found in an ASA family, which enriches the mutational profile of the ASL gene and provides a basis for genetic diagnosis of ASA. Minigenes are optimal approaches to determine whether the intron mutation can cause aberrant splicing.
| S-EPMC6533879 | biostudies-literature
Project description:Mechanisms of visual perception should be robustly fast and provide veridical information about environmental objects in order to facilitate survival and successful coping. Because species-specific brain mechanisms for fast vision must have evolved under heavy pressure for efficiency, it has been held that different human individuals see the physical world in the same way and produce psychophysical functions of visual discrimination that are qualitatively the same. For many years, this assumption has been implicitly accepted in vision research studying extremely fast, basic visual processes, including studies of visual masking. However, in recent studies of metacontrast masking surprisingly robust individual differences in the qualitative aspects of subjects' performance have been found. As the basic species-specific visual functions very likely are based on universal brain mechanisms of vision, these differences probably are the outcome of variability in ontogenetic development (i.e., formation of idiosyncrasic skills of perception). Such developmental differences can be brought about by variants of genes that are differentially expressed in the course of CNS development. The objective of this study was to assess whether visual discrimination in metacontrast masking is related to three widely studied genetic polymorphisms implicated in brain function and used here as independent variables. The findings suggest no main effects of BDNF Val66Met, NRG1/rs6994992, or 5-HTTLPR polymorphisms on metacontrast performance, but several notable interactions of genetic variables with gender, stage of the sequence of experimental trials, perceptual strategies, and target/mask shape congruence were found. Thus, basic behavioral functions of fast vision may be influenced by common genetic variability. Also, when left uncontrolled, genetic factors may seriously confound variables in vision research using masking, obscure clear theoretical interpretation, lead to unexplicable inter-regional differences and create problems of replicability of formerly successful experiments.
| S-EPMC3554658 | biostudies-literature
Project description:Pseudoexons are nonfunctional intronic sequences that can be activated by deep-intronic sequence variation. Activation increases pseudoexon inclusion in mRNA and interferes with normal gene expression. The PCCA c.1285-1416A>G variation activates a pseudoexon and causes the severe metabolic disorder propionic acidemia by deficiency of the propionyl-CoA carboxylase enzyme encoded by PCCA and PCCB. We characterized this pathogenic pseudoexon activation event in detail and identified hnRNP A1 to be important for normal repression. The PCCA c.1285-1416A>G variation disrupts an hnRNP A1-binding splicing silencer and simultaneously creates a splicing enhancer. We demonstrate that blocking this region of regulation with splice-switching antisense oligonucleotides restores normal splicing and rescues enzyme activity in patient fibroblasts and in a cellular model created by CRISPR gene editing. Interestingly, the PCCA pseudoexon offers an unexploited potential to upregulate gene expression because healthy tissues show relatively high inclusion levels. By blocking inclusion of the nonactivated wild-type pseudoexon, we can increase both PCCA and PCCB protein levels, which increases the activity of the heterododecameric enzyme. Surprisingly, we can increase enzyme activity from residual levels in not only patient fibroblasts harboring PCCA missense variants but also those harboring PCCB missense variants. This is a potential treatment strategy for propionic acidemia.
| S-EPMC10776996 | biostudies-literature
Project description:Background: Molecular genetic testing is the most sensitive and specific method to confirm acute intermittent porphyria (AIP), a rare autosomal dominant disease, caused by Hydroxymethylbilane synthase (HMBS) gene mutation. According to the Human Gene Mutation Database (HGMD), approximately 20% of the reported HMBS gene variants affect pre-RNA splicing. Thus, the ensuing challenge is how to decipher the pathogenicity of these splicing variants. Methods: Using next-generation sequencing, we identified a novel heterozygous variant in the HMBS gene (c.160 + 5G>C) from a Chinese family with AIP. And, previously, seven HMBS variants (c.33 + 5G>A, c.88-16_88-4del, c.88-2A>G, c.161-1G>C, c.652-1G>A, c.772-2A>G and c.772-1G>C) have been reported to be linked with AIP. Herein, we performed a valid and novel in vitro minigene assay to analyze the pathogenicity of these eight splicing variants. Results: By minigene assay in 293 T cell experiments, we demonstrated that all eight variants caused splicing defects in the pre-mRNA of the HMBS gene: c.160 + 5G>C (intron3p_141bp retention), c.33 + 5G>C(intron1p_91bp retention), c.88-16_88-4del and c.88-2A>G (Exon3p_15bp deletion), c.161-1G>C (Exon4p_18bp deletion), c.652-1G>A (Exon11p_1bp deletion), c.772-2A>G and c.772-1G>C (intron11q_104bp retention or Exon12p_4bp deletion).Encouragingly, the c.160 + 5G>C RNA sequencing from peripheral blood lymphocytes was consistent with the minigene assay result. Conclusion: We have made a pioneering attempt to apply minigene in vitro validation to the HMBS gene to evaluate the splicing effect of eight variants, including a novel splice variant (c.160 + 5G>C). This study provides a molecular basis for future research on the pathogenesis and gene therapy of AIP.
| S-EPMC10698471 | biostudies-literature