Search PubMed⌕ Search

Biomedical subjects

Eric A Shoubridge

Publications and source records attributed to Eric A Shoubridge.

24 records · Page 2Linked to original sources
PubMed2003

Nuclear genetic control of mitochondrial DNA segregation.

Mammalian mitochondrial DNA (mtDNA) is a high copy-number, maternally inherited genome that codes for a small number of essential proteins involved in oxidative phosphorylation. Mutations in mtDNA are responsible for a broad spectrum of clinical disorders. The segregation pattern of pathogenic mtDNA mutants is an important determinant of the nature and severity of mitochondrial disease, but it varies with the specific mutation, cell type and nuclear background and generally does not correlate well with mitochondrial dysfunction. To identify nuclear genes that modify the segregation behavior of mtDNA, we used a heteroplasmic mouse model derived from two inbred strains (BALB/c and NZB; ref. 12), in which we had previously demonstrated tissue-specific and age-dependent directional selection for different mtDNA genotypes in the same mouse. Here we show that this phenotype segregates in F2 mice from a genetic cross (BALB/c x CAST/Ei) and that it maps to at least three quantitative-trait loci (QTLs). Genome-wide scans showed linkage of the trait to loci on Chromosomes 2, 5 and 6, accounting for 16-35% of the variance in the trait, depending on the tissue and age of the mouse. This is the first genetic evidence for nuclear control of mammalian mtDNA segregation.

Animals↗
PubMed2003

Mitochondrial biogenesis: which part of "NO" do we understand?

A recent paper by Nisoli et al. [1] provides the first evidence that elevated levels of nitric oxide (NO) stimulate mitochondrial biogenesis in a number of cell lines via a soluble guanylate-cyclase-dependent signaling pathway that activates PGC1alpha (peroxisome proliferator-activated receptor gamma coactivator-1alpha), a master regulator of mitochondrial content. These results raise intriguing possibilities for a role of NO in modulating mitochondrial content in response to physiological stimuli such as exercise or cold exposure. However, whether this signaling cascade represents a widespread mechanism by which mammalian tissues regulate mitochondrial content, and how it might integrate with other pathways that control PGC1alpha expression, remain unclear.

Adenosine Triphosphate↗
PubMed2003

Prospect of preimplantation genetic diagnosis for heritable mitochondrial DNA diseases.

To perform preimplantation genetic diagnosis for women carrying heteroplasmic mitochondrial DNA (mtDNA) mutations, it is necessary to ensure that the proportion of mutant mtDNA diagnosed in the biopsied cell gives an accurate indication of the mutant load in the remaining embryo. A heteroplasmic mouse model, carrying NZB and BALB mtDNA genotypes, was used to study the relative proportions of each mtDNA genotype in the ooplasm and first polar body of mature oocytes, and between blastomeres of early cleavage stage embryos. The levels of heteroplasmy varied widely in the gametes compared with the maternal genotype. However, the distribution of the two mtDNA genotypes was virtually identical between the ooplasm and polar body of a mature oocyte, and also between the blastomeres of each 2-, 4- and 6-8-cell embryo. Therefore, the level of heteroplasmy diagnosed from the polar body of an unfertilized oocyte or from a single blastomere of an embryo is representative of the level in the embryo as a whole. Reliable results were obtained from both polar bodies and blastomeres, but the efficiency of diagnosis was greater with blastomeres. We conclude that preimplantation genetic diagnosis is feasible for mtDNA diseases, although it should be approached with caution, as it is possible that transmission of some pathogenic mutations could behave in a different manner.

Animals↗
PubMed2002

Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy.

Deficiencies in the activity of cytochrome c oxidase (COX), the terminal enzyme in the respiratory chain, are a frequent cause of autosomal recessive mitochondrial disease in infants. These patients are clinically and genetically heterogeneous, and all defects so far identified in this group have been found in genes coding for accessory proteins that play important roles in the assembly of the COX holoenzyme complex. Many patients, however, remain without a molecular diagnosis. We have used a panel of retroviral vectors expressing human COX assembly factors in these patients to identify the molecular basis for the COX deficiency by functional complementation. Here we show that overexpression of COX15, a protein involved in the synthesis of heme A, the heme prosthetic group for COX, can functionally complement the isolated COX deficiency in fibroblasts from a patient with fatal, infantile hypertrophic cardiomyopathy. Mutation analysis of COX15 in the patient identified a missense mutation (C700T) on one allele, changing a conserved arginine to tryptophan (R217W), and a splice-site mutation in intron 3 on the other allele (C447-3G), resulting in a deletion of exon 4. This splicing error introduces a frameshift and a premature stop codon, resulting in an unstable mRNA and, likely, a null allele. Mitochondrial heme A content was reduced in the patient's heart and fibroblast mitochondria, and levels of heme O were increased in the patient's heart. COX activity and the total amount of fully assembled enzyme were reduced by 50%-70% in patient fibroblasts. Expression of COX15 increased heme A content and rescued COX activity. These results suggest that reduced availability of heme A stalls the assembly of COX. This study establishes COX15 as an additional cause, along with SCO2, of fatal infantile, hypertrophic cardiomyopathy associated with isolated COX deficiency.

Age of Onset↗
PubMed2002

Nuclear genetic control of mitochondrial translation in skeletal muscle revealed in patients with mitochondrial myopathy.

Oxidative phosphorylation deficiencies can be caused by mutations in either the nuclear genome or the mitochondrial genome (mtDNA); however, most pathogenic mutations reported in adults occur in mtDNA. Such mutations often impair mitochondrial translation, and are associated with a characteristic muscle pathology consisting of a mosaic pattern of normal fibres interspersed with fibres that show mitochondrial proliferation (ragged-red fibres) and little or no complex IV (COX) activity. We investigated two adult patients with a severe mitochondrial myopathy in whom all muscle fibres showed mitochondrial proliferation with barely detectable COX activity - a pattern never before reported. Biochemical studies of the respiratory chain in muscle showed decreased activities of complexes I and IV (5% of control) and complex II+III (41% of control). Immunoblot analysis of nuclear and mitochondrial subunits of complexes I, III and IV showed a greater than 90% decrease in the steady-state level of these subunits in mature muscle, but no change in nuclear-encoded subunits of complexes II and V. A generalized mitochondrial translation defect was identified in pulse-label experiments in myotubes, but not in myoblasts cultured from both patients. This defect moved with the nucleus in patient cybrid cells. Myoblasts from one patient transplanted into the muscle bed of SCID mice differentiated into mature human muscle fibres that displayed a defect similar to that seen in the patient muscle. These results suggest a defect in a developmentally regulated nuclear factor important for mitochondrial translation in skeletal muscle.

Adult↗