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G Cortopassi

Publications and source records attributed to G Cortopassi.

26 records · Page 2Linked to original sources
PubMed1994

Mice with duplications and deletions at the Tme locus have altered MnSOD activity.

Superoxide radicals that result from normal cellular metabolism have been implicated as a cause of multiple age-related degenerative diseases (Halliwell, B., and Gutteridge, J. M. (1990) Methods Enzymol. 186, 1-85; Harman, D. (1988) Mol. Cell. Biochem. 84, 155-161; Ames, B. N., Shigenaga, M. K., and Hagen, T. M. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 7915-7922). Manganese superoxide dismutase (MnSOD) is thought to be the sole enzymic scavenger of superoxide in mammalian mitochondria. We have investigated MnSOD activity and gene dose in mice with deletions and a duplication of the Tme (t-associated maternal effect) locus on chromosome 17. We find that MnSOD activity is significantly correlated with gene dose in these animals; animals with heterozygous deletions of Tme have 50% of normal activity, and animals with a heterozygous duplication of Tme have 150% of normal activity. These ratios of activity appear to be systemic, as they were observed in brain, heart, skeletal muscle and liver. The results support the model that basal MnSOD activity is regulated solely by cis elements, in that variation in MnSOD activity caused by altered gene dose on one chromosome is not compensated by gene activity on the other. Since gene knockouts of MnSOD have not yet been generated, the tlub2 and Thp animals may become useful models for those studying the role of mitochondrial superoxide in pathophysiological processes. A model for the maternal-lethal effect of Tme deletions is proposed.

Animals↗
PubMed1994

A molecular and cellular hypothesis for aminoglycoside-induced deafness.

The ototoxic effects of aminoglycoside antibiotics are well known. However, a molecular and cellular mechanism for the death of cochlear hair cells has remained difficult to prove. Human genetic studies have shown that a rare trait for hypersensitivity to aminoglycosides is conferred by mitochondrial genetic variation. Recently, a gene involved has been identified as the mitochondrial small ribosomal RNA gene, consistent with the known mechanism of aminoglycoside action against bacteria. We used the existing data as a basis for our hypothesis of a molecular and cellular model for aminoglycoside ototoxicity that is described in this paper.

Aminoglycosides↗
PubMed1993

A molecular basis for human hypersensitivity to aminoglycoside antibiotics.

We have investigated the distribution of mitochondrial DNA polymorphisms in a rare maternally transmitted genetic trait that causes hypersensitivity to aminoglycoside antibiotics, in the hope that a characterization of its molecular basis might provide a molecular and cellular understanding of aminoglycoside-induced deafness (AGD). Here we report that the frequency of a particular mitochondrial DNA polymorphism, 1555G, is associated nonrandomly with aminoglycoside-induced deafness in two Japanese pedigrees, bringing the frequency of this polymorphism to 5 occurrences in 5 pedigrees of AGD, and in 4 of 78 sporadic cases in which deafness was thought to be the result of aminoglycoside exposure; both frequencies are significantly different from the occurrence of this mutation in the hearing population, which was 0 in 414 individuals surveyed. The 1555G polymorphism occurred in none of 34 aminoglycoside-resistant individuals. We propose a specific molecular mechanism for aminoglycoside hypersensitivity in individuals carrying the 1555G polymorphism, based on the three-dimensional structure of the ribosome, in which the 1555G polymorphism favors aminoglycoside binding sterically, by increasing access to the the ribosome cleft.

Adolescent↗
PubMed1992

Deleterious mitochondrial DNA mutations accumulate in aging human tissues.

This paper reviews the current state of knowledge of the contribution of mitochondrial DNA (mtDNA) mutations to the phenotype of aging. Its major focus is on the discovery of deletions of mtDNA which previously were thought to occur only in individuals with neuromuscular disease. One particular deletion (mtDNA4977) accumulates with age primarily in non-dividing cells such as muscle and brain of normal individuals. The level of the deletion rises with age by more than 1000 fold in heart and brain and to a lesser extent in other tissues. In the brain, different regions have substantially different levels of the deletion. High levels of accumulation of the deletion in tissues are correlated with high oxygen consumption. We speculate that oxidative damage to mtDNA may be 'catastrophic'; mutations affecting mitochondrially encoded polypeptides involved in electron transport could increase free radical generation leading to more mtDNA damage.

Aging↗
PubMed1992

Mosaicism for a specific somatic mitochondrial DNA mutation in adult human brain.

The levels of a specific mitochondrial DNA deletion (mtDNA4977) measured in 12 brain regions of 6 normal adults 39 to 82 years old exhibited striking variation among anatomical locations. Comparisons of the same region among individuals showed an increase of mtDNA4977 with age. The three regions with the highest levels, caudate, putamen and substantia nigra, are characterized by a high dopamine metabolism. The breakdown of dopamine by mitochondrial MAO produces H2O2 which can lead to oxygen radical formation. We suggest that mtDNA4977 may be the "tip of the iceberg" of the spectrum of somatic mutations produced by oxidative damage.

Adult↗
PubMed1989

A simple method for site-directed mutagenesis using the polymerase chain reaction.

We have developed a general and simple method for directing specific sequence changes in a plasmid using primed amplification by the polymerase chain reaction (PCR). The method is based on the amplification of the entire plasmid using primers that include the desired changes. The method is rapid, simple in its execution, and requires only minute amounts of plasmid template DNA. It is significant that there are no special requirements for appropriately placed restriction sites in the sequence to be manipulated. In our system the yield of transformants was high and the fraction of them harboring plasmids with only the desired change was consistently about 80%. The generality of the method should make it useful for the direct alteration of most cloned genes. The only limitation may be the total length of the plasmid to be manipulated. During the study we found that the Taq DNA polymerase used for PCR adds on a single extra base (usually an A) at the end of a large fraction of the newly synthesized chains. These had to be removed by the Klenow fragment of DNA polymerase to insure restoration of the gene sequence.

Base Sequence↗
PubMedDate not supplied

Degeneration of human oncogenes and mitochondrial genes occurs in cells that exhibit age-related pathology.

The development of a new class of assays to determine in vivo mutation frequencies has provided new perspectives on the timing, location, and distribution of somatic mutagenesis in mitochondrial genes and in oncogenes of the aging human body. This descriptive information has led to the inference of new models for age-related pathophysiology and oncogenesis. Mutations of mitochondrial genes rise rapidly with age to frequencies a thousand-fold higher than those of nuclear genes. Genotypic selection analysis has revealed that mitochondrial mutations accumulate predominantly in nonmitotic cells whose age-dependent loss is associated with pathology. Random mitochondrial mutation is most likely to inactivate Complex I, deficiency of which induces mitochondrial superoxide formation and cell death. Genotypic selection of oncogenic mutations at the BCL2 and p53 loci has revealed that the cell specificity of oncogenic mutations in persons without cancer correlates well with sites of tumor origin, indicating that cells bearing such mutations are the likely precursors of future tumors. Quantitative variation in human BCL2 mutation frequency is extensive, and BCL2 mutation frequency rises with age, concordant with increased risk for lymphoma. The clonality and persistence of BCL2 mutations suggests two specific testable mechanisms of lymphomagenesis. BCL2 mutation frequency rises in persons exposed to cigarette smoke, and more p53 mutations occur in skin exposed to sunlight than in unexposed skin. Thus, in addition to their likely relevance to future cancer risk, the dose-response relationship between exposure and oncogenic mutations indicates promise for their future use as in vivo biodosimeters of human exposure to carcinogens.

Aging↗