Project description:The dataset includes exome sequencing results for a patient with SSBP1 mutations that cause a complex optic atrophy spectrum disorder
Project description:The genetic defects leading to optic atrophy range from mitochondrial DNA (mtDNA) point mutations in Leber’s hereditary optic neuropathy (LHON), to dominant and recessive mutations affecting a cluster of nuclear genes implicated in mitochondrial dynamics. We performed WES in patients with an optic atrophy spectrum disorder, including retinal macular dystrophy and kidney insufficiency leading to transplantation, associated with mitochondrial DNA (mtDNA) depletion without accumulation of multiple deletions, to identify the genetic causes of this syndrome.
Project description:The nuclear receptor Nr2f1 acts as a strong transcriptional regulator in embryonic and postnatal neural cells. In humans, its mutations cause the Bosch-Boonstra-Schaaf optic atrophy-intellectual syndrome (BBSOAS), a rare neurodevelopmental disorder characterized by multiple clinical features including optic nerve atrophy, intellectual disability, and autistic traits. In this study, by genome-wide and in silico analyses we identified a wide set of nuclear-encoded mitochondrial genes as potential genomic targets under direct Nr2f1 transcriptional control in neurons. By combining mouse genetics, neuroanatomical and imaging approaches we demonstrated that conditional Nr2f1 loss-of-function within the adult mouse hippocampal neurogenic niche results in a reduced mitochondrial mass associated with mitochondrial fragmentation and downregulation of key mitochondrial proteins in newborn neurons, whose functional integration and survival are impaired. Importantly, we also found dysregulation of several mitochondrial genes and downregulation in levels of key mitochondrial proteins in the brain of mice heterozygous for Nr2f1, a validated BBSOAS model. Our data point to an active role of Nr2f1 in the mitochondrial gene expression regulatory network in neurons and support the involvement of mitochondrial dysfunction in BBSOAS pathogenesis.
Project description:Recessive mutations in EXOSC3, encoding a subunit of the human RNA exosome complex, cause Pontocerebellar hypoplasia type 1b (PCH1B). We report a boy with severe muscular hypotonia, psychomotor retardation, progressive microcephaly, and cerebellar atrophy. Biochemical abnormalities comprised mitochondrial Complex I and PDHc deficiency. Whole exome sequencing uncovered a known EXOSC3-mutation p.(D132A) as the underlying cause. In patient fibroblasts, >50% of the EXOSC3 protein was trapped in the cytosol. mtDNA-copy numbers in muscle were reduced to 40%, but mutations in the mtDNA and nuclear mitochondrial genes were excluded. RNA-seq of patient muscle showed highly increased mRNA-copy numbers, especially for genes encoding structural subunits of OXPHOS-complexes I, III, and IV, possibly due to reduced degradation by a dysfunctional exosome complex. This is the first case of mitochondrial dysfunction associated with an EXOSC3 mutation, which expands the phenotypic spectrum of PCH1B. We discuss the links between exosome and mitochondrial dysfunction.
Project description:Mitochondria are critical for metabolic homeostasis of the liver, and thus, mitochondrial dysfunction is a major cause of liver diseases. Optic atrophy 1 (OPA1) is a mitochondrial fusion protein that also plays a role in cristae shaping. Hence, the OPA1 gene disruption has been shown to cause mitochondrial dysfunction. However, the role of OPA1 in liver function is poorly understood. In this study, we deleted OPA1 in fully developed mouse liver and examined its effect.
Project description:Autosomal dominant cerebellar ataxia, deafness, and narcolepsy (ADCA-DN) is a late onset disorder, due to mutations in DNA methyltransferase type 1 (DNMT1). Yet our understanding of how these mutations in DNMT1 lead to the clinical phenotypes of ADCA-DN is still unclear. To address this, we used fibroblasts, induced pluripotent stem cells (iPSCs) and induced neurons (iNs) generated from patients with ADCA-DN and controls, to determine the underlining epigenomic changes. Here we show that the differential expression pattern and differential methylation spectrum between patients and controls were tissue-specific. Furthermore, methylation and gene expression changes were negatively correlated in iPSCs and iNs. In addition, we identified a group of genes associated with clinical phenotypes of ADCA-DN, including PDGFB and PRDM8 for cerebellar ataxia, psychosis and dementia, and NR2F1 for deafness and optic atrophy. We further showed that ZFP57, which is required to maintain gene imprinting through DNA methylation during early development, was hypomethylated in promoters and exhibited upregulated expression in patients with ADCA-DN in both iPSC and iNs. Our results provide insight into the molecular changes associated with ADCA-DN, with potential implications for genes associated with related phenotypes.
Project description:Single-stranded DNA or RNA sequences rich in guanine (G) can adopt non-canonical structures known as G-quadruplexes (G4). G4 in the mitochondrial genome are heavy-strand enriched and have been associated with the formation of deletion breakpoints that cause mitochondrial diseases. However, the functional role of G4 structures in mitochondria remains unclear. Here, we have identified RHPS4 as a G4-specific ligand that localizes to mitochondria and causes replication pausing, with mitochondrial DNA (mtDNA) depletion occurring at higher dosage. We further show that RHPS4 interferes with mitochondrial transcript elongation at low doses, leading to respiratory complex depletion. These unprecedented observations suggest that G4 motifs modulate mitochondrial transcription and replication efficiency. Using the differential effects of high vs low RHPS4 dosing, we characterized gene expression pathway responses to mitochondrial transcription inhibition or mitochondrial genome depletion. Importantly, a human mtDNA mutation that increases G4 formation potential strongly enhanced the RHPS4-mediated mitochondrial respiratory defect. We propose that abnormal G4 dynamics may contribute to mtDNA instability and gene expression defects, particularly in the presence of mitochondrial mutations that enhance the G4 formation.