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J Montoya

Publications and source records attributed to J Montoya.

At least 91 records · Page 5Linked to original sources
PubMed1981

Distinctive features of the 5'-terminal sequences of the human mitochondrial mRNAs.

The 5'-end proximal sequences of all the putative mRNAs coded for by the heavy strand of HeLa cell mitochondrial DNA have been determined and aligned with the DNA sequence. All these mRNAs start directly at, or very near to, an AUG or AUA triplet, with the exception of one which starts at an AUU. The available evidence indicates that the terminal or subterminal AUGs and AUAs, and possibly also the terminal AUU, are initiator codons for the corresponding polypeptides. In most cases, the individual mRNA coding sequences are flanked on their 5' side by a tRNA gene, without any intervening nucleotide.

Base Sequence↗
PubMed1981

tRNA punctuation model of RNA processing in human mitochondria.

A 3'-end proximal segment of most of the putative mRNAs encoded in the heavy strand of HeLa cell mtDNA has been partially sequences and aligned with the DNA sequence. In all cases, the 3'-end nucleotide of the individual mRNA coding sequences has been found to be immediately contiguous to a tRNA gene or another mRNA coding sequence. These and previous results indicate that the heavy (H) strand sequences coding for the rRNA, poly(A)-containing RNA and tRNA species form a continuum extending over almost the entire length of this strand. We propose that the H strand is transcribed into a single polycistronic RNA molecule, which is processed later into mature species by precise endonucleolytic cleavages which occur, in most cases, immediately before and after a tRNA sequence.

DNA, Mitochondrial↗
PubMed1980

The putative mRNA for subunit II of human cytochrome c oxidase starts directly at the translation initiator codon.

The gene for subunit II of cytochrome c oxidase (COII) in human mitochondrial DNA (mtDNA) is immediately contiguous, on its 5'-end side, to a tRNAAsp gene. Since all eukaryotic mRNAs so far analysed have been shown to have a noncoding stretch, which is presumably used for ribosome attachment on the 5'-side of the coding sequence, it was resonable to ask whether, in the case of the human COII mRNA, the above function is performed by the tRNAAsp sequence or a portion of it, or whether this mRNA lacks a 5' noncoding stretch. We have sequenced a 5'-end proximal segment of the putative COII mRNA from HeLa cells of about 30 nucleotides and have aligned it with the COII coding sequence in human mtDNA. Our results show that this RNA starts directly at the AUG initiator codon.

Base Sequence↗
PubMed1980

Mitochondrial heterogeneity in Aspergillus nidulans: evidence of in vivo transformation among different mitochondrial populations.

The distribution of mitochondria from Aspergillus nidulans on a dextran-sucrose gradient resulted in the fractionation of three bands. The lightest band presented the highest respiratory and cytochrome c oxidase activities and was also the most active in the incorporation of tritiated glycerol. Pulse-chase experiments with 3H-glycerol suggested that mitochondria from the light band was transformed to denser organelles as the organism grew.

Aspergillus nidulans↗
PubMed1980

Mitochondrial heterogeneity in Aspergillus nidulans: in vivo protein biosynthetic activities of the mitochondrial populations.

Two mitochondrial populations with cytochrome c oxidase activity, and densities of 1.07 and 1.08 g/ml have been separated by means of a dextran-sucrose gradient. The highest enzymatic specific activity appeared in the 1.07 g/ml band. The mitochondria assayed by their in vivo cycloheximide resistant leucine incorporation appeared at the 1.08 g/ml density band of the gradient. Some amount of activity of cytochrome c oxidase, and leucine incorporation appeared at the bottom of the gradient. The cytochrome spectra in liquid nitrogen of each band showed different proportion of cytochrome(s) a, b and c. The highest ratio of cytochrome a and cytochrome b in respect to cytochrome c appeared in the 1.08 g/ml band.

Aspergillus nidulans↗
PubMedDate not supplied

Autonomous regulation in mammalian mitochondrial DNA transcription.

The regulation of the oxidative phosphorylation system (OXPHOS) biogenesis in eukaryotic cells is unique since it involves the expression of two genomes, the mitochondrial DNA (mtDNA) and the nuclear DNA (nDNA). The considerable effort done in collecting information on the factors that influence the expression of the genes encoded in mtDNA and nDNA has revealed that a multiplicity of regulatory options are available in mammalian cells to perform this task. Thus, at least three archetypal situations can be distinguished: mitochondrial proliferation, mitochondrial differentiation, and mitochondrial local tuning (MLT). Each of them seems to be predominantly under the control of specific strategies of regulation, although the description of the detailed molecular mechanisms involved is still in its beginnings. In the present review, we focus on the evidence supporting the existence of mechanisms for autonomous regulation of mtDNA transcription and its role in the integrated regulation of the OXPHOS system biogenesis.

Animals↗
PubMedDate not supplied

Development of Colombian isolates of Leishmania (Viannia) panamensis, Le. (V.) guyanensis and Le. (V.) braziliensis in the sandfly Lutzomyia intermedia (Lutz & Neiva, 1912) under experimental conditions.

The development of Colombian Leishmania species of the subgenus Viannia in Lutzomyia intermedia was similar to that observed with Brazilian Le. (V.) braziliensis: colonization of the pylorus by paramastigotes; promastigotes in the midgut and massive infection of stomodeal valve. Difference was observed in the number of paramastigotes colonizing the pylorus, which was smaller in Colombian Leishmania species than Brazilian Le. braziliensis.

Animals↗
PubMedDate not supplied

[Recent advances in genetics of epilepsy. Genetic of mitochondrial epilepsy].

INTRODUCTION: Recently the molecular basis of a series of clinical disorders associated with defects in the oxidative phosphorylation system (OXPHOS system) leading to ATP synthesis, the final pathway of mitochondrial energy metabolism, has been established. The polypeptide components of the OXPHOS system are codified in both nuclear and mitochondrial DNA. Therefore these mitochondrial diseases may be originated by mutations of genes found in both genetic systems. DEVELOPMENT: In recent years, several such neuromuscular diseases have been defined and associated with mitochondrial DNA mutations. One of the most striking of these is the syndrome of myoclonic epilepsy with ragged red fibres (MERRF), characterized by myoclonic epilepsy of maternal inheritance. This disorder is caused by a specific mutation on the mitochondrial tRNA(Lys) (position 8344), which gives rise to a reduction in the level of lysil-tRNA(Lys) and thus to premature termination of the translation of proteins codified in the mitochondrial DNA.

DNA, Mitochondrial↗
PubMedDate not supplied

[Molecular studies in Cuban patients with progressive external ophthalmoplegia].

INTRODUCTION: The mitochondria, subcellular organelles which possess their own DNA (mtDNA), produce most of the energy, in the form of ATP, which is necessary for life. This mtDNA may have diverse molecular defects which have been associated with a great variety of clinical syndromes. Deletions in mtDNA are one of the common mutations in patients with mitochondrial myopathies, which in the great majority present with the common symptom of progressive external ophthalmoplegia. In this study we report our findings in eight Cuban families with suspected mitochondrial disease. OBJECTIVES: To characterize these patients from the molecular point of view, which would allow a preliminary understanding of the behavior of these deletions in Cuban patients. PATIENTS AND METHODS: We studied nine patients from eight Cuban families in whom mitochondrial encephalomyopathy was suspected. We analyzed the presence of ragged red fibres, the enzymatic activity of the mitochondrial respiratory chain and detection of mtDNA mutations. We used the technique of restriction length polymorphism analysis for detection of deletions. RESULTS: Histochemical studies showed the presence of COX negative ragged red fibres in seven of the patients studied. The enzymatic activity of the mitochondrial respiratory chain was normal in all the patients. We detected four patients with single deletions of mtDNA, and one with multiple deletions and of the patients had the A3243G mutation. CONCLUSIONS: With the methods used we were able to determine the presence of a mitochondrial disorder in seven of the eight families studied and deletions of mtDNA were detected as the cause of the illness in five. The disorder was always associated with progressive external ophthalmoplegia and COX negative ragged red fibres.

Adolescent↗
PubMedDate not supplied

[Aspects of neuropathy in mitochondrial diseases].

INTRODUCTION: The existence of neuropathy has been described in mitochondrial disorders such as MELAS, MERRF, Leigh's syndrome, the Kearns-Saye syndrome, myoneurogastro-intestinal encephalopathy and progressive external ophthalmoplegia and constitutes a basic component of the NARP (neuropathy, ataxia and retinosis pigmentosa). However, the general prevalence of the neuropathy and its characteristics within the mitochondrial encephalopathies is not well understood. OBJECTIVES: To characterize the neuropathy and try to establish a genotype-phenotype correlation. PATIENTS AND METHODS: Within study guidelines, we made a retrospective study of 27 patients, diagnosed as having mitochondrial disease, who had had neurophysiological studies (EMG-ENG). In those in whom neuropathy had been found we analysed the clinical, neurophysiological and genetic characteristics. RESULTS: Neuropathy was present in 37% of the patients who had an average age of 13 years, ranging from 1 to 25 years. Syndromic diagnoses were: 7 encephalomyopathies, one MELAS, one MERRF and one NARP. Four of the patients were classified genetically. In all but two of the patients the neuropathy was asymptomatic. The biochemical alterations seen were: deficit of Complex 1 in 3 patients, of complex III in 3 patients, of complex IV in 2 and of pyruvate dehydrogenase in one patient. The type of neuropathy found was varied, with predominance of axonal-type motor neuropathy but no correlation with either biochemical defects or genetic diagnosis. CONCLUSIONS: Neuropathy is a common finding in mitochondrial disorders and probably is under-diagnosed. The axonal form predominates. We have not been able to establish correlations between phenotypes and genotypes.

Adolescent↗
PubMedDate not supplied

[Diseases of mitochondrial DNA].

INTRODUCTION: Human diseases caused by disorders of the mitochondrial metabolism have been described more than 30 years ago. Some of these are associated to defects in the oxidative phosphorylation system (OXPHOS system), the final pathway of the mitochondrial energetic metabolism, that leads to the synthesis of ATP. DEVELOPMENT: Part of the polypeptide subunits involved in the OXPHOS system are codified by the mitochondrial DNA (mtDNA). In the last 12 years, mutations (point mutations or deletions) in the mtDNA have been described and associated to well defined clinical syndromes caused by defects in the OXPHOS system. The clinical features of these diseases are very heterogeneous affecting in most cases to a great variety of organs and tissues. CONCLUSIONS: The correct diagnosis of these mitochondrial disorders require precise clinical, morphological, biochemical, and genetic data. The rapid advances in genetic analysis allow the rapid detection of mutations, even before the obtention of other type of analysis.

DNA Mutational Analysis↗
PubMedDate not supplied

[Mitochondrial encephalomyelitis, lactic acidosis and cerebrovascular accidents (MELAS) in pediatric age with the A3243G mutation in the tRNALeu(UUR) gene of mitochondrial DNA].

OBJECTIVES: To evaluate three patients with the mitochondrial encephalopathy, lactic acidosis and cerebrovascular accident syndrome (MELAS) diagnosed in childhood, with particular reference to the initial symptoms and clinical evolution during the first stage at a pediatric age, and to compare them with other studies on the subject. PATIENTS AND METHODS: Two boys and a girl of 10, 11 and 13 years had tests on lactate, pyruvate and aminoacids in biological fluids under basal conditions and also functional tests and enzyme activity assay of the mitochondrial respiratory chain of a muscle biopsy. We also analysed the particular DNA mutations related to MELAS in different tissues from these patients and in lymphocytes from members of the mothers' families who could be tested. RESULTS: The patients fulfilled the clinical criteria for the MELAS syndrome. Neuroimaging showed cerebrovascular accidents. Neurophysiological studies showed myopathy in one patient and neuroaxonal neuropathy in another. In two cases ophthalmological study showed retinitis pigmentaria and during cerebrovascular accidents transient phenomena of homonymous hemianopsia and cortical blindness were seen. In all patients muscle biopsy showed ragged red fibres and the biochemical study showed an enzyme deficit in the respiratory mitochondrial chain. On molecular genetic study of the mitochondrial DNA (mtDNA) there was a particular mutation A3243G on the tRNA(Leu) in all patients and some members of the mothers' families. CONCLUSIONS: In children with frequent episodes of migraine headaches, vomiting, refractory epilepsy and fatigue the presence of a mitochondrial disease should be suspected. On detection of mtDNA mutations MELAS may be diagnosed even without all the clinical criteria which characterise this syndrome.

Child↗
PubMedDate not supplied

[Genetic diseases of the mitochondrial DNA in humans].

Mitochondrial diseases are a group of disorders produced by defects in the oxidative phosphorylation system (Oxphos system), the final pathway of the mitochondrial energetic metabolism, resulting in a deficiency of the biosynthesis of ATP. Part of the polypeptide subunits involved in the Oxphos system are codified by the mitochondrial DNA. In the last years, mutations in this genetic system have been described and associated to well defined clinical syndromes. The clinical features of these disorders are very heterogeneous affecting, in most cases, to different organs and tissues and their correct diagnosis require precise clinical, morphological, biochemical and genetic data. The peculiar genetic characteristics of the mitochondrial DNA (maternal inheritance, polyplasmia and mitotic segregation) give to these disorders very distinctive properties. The English version of this paper is available at: http://www.insp.mx/salud/index.html.

Adenosine Triphosphate↗
PubMedDate not supplied

[Leigh syndrome resulting from a de novo mitochondrial DNA mutation (T8993G)].

INTRODUCTION: Several degenerative neurological diseases are caused by mutations in the mitochondrial gene coding for subunit 6 of the ATPase. Thus, NARP (neurogenic weakness, ataxia, and retinitis pigmentosa) and Leigh syndromes are associated to a T8993G mutation when the percentage of mutant mitochondrial DNA is low (60 90%) or high (>90%), respectively. Leigh syndrome is also caused by a second mutation in the same position T8993C. CASE REPORT: The patient, a boy that died at 6 months, had generalized hypotonia, psychomotor delay, hepatomegaly, choreic movements and hyporreflexia. MRI showed hypodensities in the basal ganglia and brain stem as well as hyperlactacidemia. Molecular genetic analysis of the mitochondrial DNA showed that the patient had the T8993G mutation in a percentage higher than 95%. No mutated DNA was detected in blood of the proband s mother, maternal aunt and grandmother. CONCLUSIONS: The point mutation T8993G may occur de novo, at high levels, causing neurodegenerative diseases.

DNA, Mitochondrial↗
PubMedDate not supplied

[A single deletion of mitochondrial DNA in a Brazilian patient with chronic progressive external ophthalmoplegia].

INTRODUCTION: The syndrome of chronic progressive external ophthalmoplegia (CPEO) has been associated to the presence of large deletion, single or multiple, in the mitochondrial DNA of skeletal muscle. CASE REPORT: We report a sporadic case of chronic progressive external ophthalmoplegia that began at age 19 years and was associated with ragged red fibers in skeletal muscle. Genetic analysis of mitochondrial DNA revealed the presence of a single deletion of 4237 bp that encompasses the nucleotide positions 9486 to 13722, a location that has not been described before, and flanked by a direct repeat sequence. The deletion is flanked by a direct repeat. CONCLUSIONS: The amount of deleted mitochondrial DNA (55%) in this patient's muscle suggests that this deletion is the molecular cause of the phenotypic presentation of this patient.

Adult↗