Biomedical subjects

A Moya

Publications and source records attributed to A Moya.

At least 109 records · Page 6Linked to original sources

PubMed1992

Phylogenetic reconstruction of the Drosophila obscura group, on the basis of mitochondrial DNA.

We have constructed restriction-site maps of the mtDNAs in 13 species and one subspecies of the Drosophila obscura group. The traditional division of this group into two subgroups (affinis and obscura) does not correspond to the phylogeny of the group, which shows two well-defined clusters (the Nearctic affinis and pseudoobscura subgroups) plus a very heterogeneous set of anciently diverged species (the Palearctic obscura subgroup). The mtDNA of Drosophila exhibits a tendency to evolve toward high A+T values. This leads to a "saturation" effect that (1) begets an apparent decrease in the rate of evolution as the time since the divergence of taxa increases and (2) reduces the value that mtDNA restriction analysis has for the phylogenetic reconstruction of Drosophila species that are not closely related.

Animals↗

PubMed1992

Pear blister canker viroid is a member of the apple scar skin subgroup (apscaviroids) and also has sequence homology with viroids from other subgroups.

The sequence of pear blister canker viroid (PBCVd), the putative causal agent of pear blister canker (PBC) disease, has been determined. PBCVd consists of a single-stranded circular RNA of 315 nucleotide residues which assumes a branched conformation when it is folded in the model of lowest free energy. PBCVd has highest sequence similarity with grapevine 1B viroid (52.4%), but also contains sequences related to regions present in viroids that belong to different subgroups, suggesting that PBCVd could have developed from RNA recombination between viroids replicating in a common host plant. PBCVd contains almost the entire central sequence which is conserved in the members of the apple scar skin subgroup (apscaviroids) as well as a conserved sequence located in the left-terminal region of apscaviroids and pospiviroids (whose type member is potato spindle tuber viroid). A consensus phylogenetic tree has been obtained in which PBCVd and other viroids previously classified as apscaviroids appear closely related, allowing consideration of PBCVd as a new member of this subgroup.

Base Sequence↗

PubMed1991

Fixation of mutations at the VP1 gene of foot-and-mouth disease virus. Can quasispecies define a transient molecular clock?

The number of nucleotide (nt) substitutions found in the VP1 gene (encoding viral capsid protein) between any two of 16 closely related isolates of foot-and-mouth disease virus (FMDV) has been quantified as a function of the time interval between isolations [Villaverde et al., J. Mol. Biol. 204 (1988) 771-776]. One of them (isolate C-S12) includes some replacements found in isolates that preceded it and other replacements found in later isolates. The study has revealed alternating periods of rapid evolution and of relative genetic stability of VP1. During a defined period of acute disease, the rate of fixation of replacements at the VP1 coding segment was 6 x 10(-3) substitutions per nt per year. Only small differences in the rate of evolution were observed between subsegments within the VP1 gene. The observation of a relatively constant rate of evolution during a disease episode was unexpected. We propose that such constancy may be a consequence of random sampling of mutants from the FMDV quasispecies, followed by their amplification in susceptible hosts (to generate a new quasispecies). Successive sampling and amplification events may result in a steady accumulation of mutations.

Amino Acid Sequence↗

PubMed1991

Phylogeny of viroids, viroidlike satellite RNAs, and the viroidlike domain of hepatitis delta virus RNA.

We report a phylogenetic study of viroids, some plant satellite RNAs, and the viroidlike domain of human hepatitis delta virus RNA. Our results support a monophyletic origin of these RNAs and are consistent with the hypothesis that they may be "living fossils" of a precellular RNA world. Moreover, the viroidlike domain of human hepatitis delta virus RNA appears closely related to the viroidlike satellite RNAs of plants, with which it shares some structural and functional properties. On the basis of our phylogenetic analysis, we propose a taxonomic classification of these RNAs.

Hepatitis Delta Virus↗

PubMed1991

Evolution of the G and P genes of human respiratory syncytial virus (subgroup A) studied by the RNase A mismatch cleavage method.

The G and P genes of human respiratory syncytial viruses (subgroup A), isolated between 1961 and 1989, were analyzed by RNase A one-dimensional fingerprinting, using the Long strain as the reference. Total RNA extracted from cells infected with the different isolates was hybridized to radiolabeled antisense G or P RNA probes of the Long virus. The RNA:RNA heteroduplexes were digested with RNase A and the resistant products analyzed by gel electrophoresis. Comparative analysis of the cleavage patterns revealed extensive genetic heterogeneity in both genes among viruses isolated in different epidemics. In contrast, 13 viruses isolated in Montevideo during a 3-month period showed much more restricted heterogeneity; thus, 11 viruses represented the predominant type of this outbreak and only 2 other viruses generated different RNA cleavage patterns distantly related to the major type. Statistical analysis of the results obtained indicated progressive accumulation of genetic changes with time along cocirculating evolutionary lineages within the same antigenic subgroup of RS virus. The results are discussed in terms of a model for RS virus evolution.

Antigens, Viral↗

PubMed1991

Repetitive nucleotide sequencing of a dispensable DNA segment in a clonal population of African swine fever virus.

Repetitive nucleotide sequencing of a dispensable genomic segment of a clonal population of African swine fever (ASF) virus has been carried out to estimate the mutant frequency to neutral alleles. Since no mutations have been detected in a total of 54026 nucleotides screened, the maximum mutant frequency is 5.5 x 10(-5) substitutions/nucleotide (95% confidence level). The result renders very unlikely the occurrence of hypermutational events during ASF virus DNA replication, at least within the selected DNA fragment.

African Swine Fever Virus↗

PubMed1991

Fertility and viability at the Sod locus in Drosophila melanogaster: non-additive and asymmetric selection.

Experiments were designed to test in Drosophila melanogaster the effect of mating type at the Sod locus on fertility and viability. The experiments show that fertility is neither additive (or multiplicative) nor symmetric, i.e. that the fertility of a mating type cannot be predicted from the average fertility of the two genotypes involved in the mating. There is no significant male x female interaction with respect or progeny viability; but the interaction is significant for productivity, i.e. when fertility and viability are jointly taken into account. There is overdominance with respect to female fertility, but not with respect to male fertility or to viability. There also is alloprocoptic selection with respect to fertility and with respect to productivity, i.e. mating between like homozygotes are less fertile and productive than matings between dissimilar homozygotes. Selection at the Sod locus yields stable polymorphic equilibria, with the frequency of the F allele predicted at P = 0.641 or 0.695, respectively for low and high larval density.

Animals↗

PubMed1991

Two modes of balancing selection in Drosophila melanogaster: overcompensation and overdominance.

Overdominance is often invoked to account for the extensive polymorphisms found in natural populations of organisms; overcompensation, however, may be equally or more important. Overcompensation occurs when limiting resources are better exploited by a genetically mixed than by a uniform population, and is often causally related to frequency-dependent selection. We have designed experiments to test whether overcompensation occurs in Drosophila melanogaster, using the Sod locus as a marker. Tests are made at each of two densities and two temperatures for cultures with desired genetic compositions. Both temperature and density have statistically significant effects on the per-female productivity of the cultures. More important, there are strong effects due to overcompensation. Cultures that are more polymorphic are also more productive than less polymorphic ones even when the level of individual heterozygosity is the same in all. There is also overdominance for the Sod locus: the heterozygotes are more productive than either homozygote at every temperature and density, and the differences are statistically significant in several cases. These results corroborate previous studies showing that overdominance may contribute to the maintenance of the Sod polymorphisms. Moreover, our results indicate that the significance of overcompensation as a mechanism to account for polymorphism in natural populations deserves further investigation.

Analysis of Variance↗

PubMed1991

Fitness alteration of foot-and-mouth disease virus mutants: measurement of adaptability of viral quasispecies.

We document the rapid alteration of fitness of two foot-and-mouth disease virus (FMDV) mutants resistant to a neutralizing monoclonal antibody. Both mutants showed a selective disadvantage in BHK-21 cells when passaged in competition with their parental FMDV. Upon repeated replication of the mutants alone, they acquired a selective advantage over the parental FMDV and fixed additional genomic substitutions without reversion of the monoclonal antibody-resistant phenotype. Thus, variants that were previously kept at low frequency in the mutant spectrum of a viral quasispecies rapidly became the master sequence of a new genomic distribution and dominated the viral population.

Amino Acid Sequence↗

PubMed1990

Sequences of isopenicillin N synthetase genes suggest horizontal gene transfer from prokaryotes to eukaryotes.

Evolutionary distances between bacterial and fungal isopenicillin N synthetase (IPNS) genes have been compared to distances between the corresponding 5S rRNA genes. The presence of sequences homologous to the IPNS gene has been examined in DNAs from representative prokaryotic organisms and Ascomycotina. The results of both analyses strongly support two different events of horizontal transfer of the IPNS gene from bacteria to filamentous fungi. This is the first example of such a type of transfer from prokaryotes to eukaryotes.

Acremonium↗

PubMed1990

Overcompensation as a mechanism for maintaining polymorphism: egg-to-adult viability in Drosophila.

Frequency-dependent selection may be accounted for, in ecological terms, by the differential effectiveness of alternative genotypes in exploiting limiting environmental resources. Differentiation in resource exploitation among genotypes implies in turn that a mix of genotypes may exploit more fully the resources than a genetically uniform population, a phenomenon called 'overcompensation'. Experiments designed to test for overcompensation show that highly polymorphic populations can support larger numbers of individuals per food unit than less polymorphic populations. This difference cannot be attributed to the level of individual heterozygosity, which is the same in both types of populations.

Animals↗

PubMed1990

Larval competition in Drosophila melanogaster: effects on development time.

The effects on development time of larval competition that is interrupted at different times are analyzed in an experiment with constant larval density and varying proportions of two competing strains. Interruption of competition is carried out by means of the overfeeding technique, which allows for the study of individuals that, after several days under competition stress, either complete their development in crowded conditions or migrate to a vial with fresh food where the rest of their development takes place. Results of mean development time and within-vial variance of development time show that individuals under strong competition stress can arrest their development retaining the capability to resume it, once they are exposed to fresh food. The effects of competition are observed sooner on development time than on viabilities, which is in agreement with Ohba's observations (Biol. J. Okayama Univ. 7:87-125, 1961), but the observed effects are not always coincident for both fitness components.

Analysis of Variance↗

PubMed1990

Comparison of vaccine strains and the virus causing the 1986 foot-and-mouth disease outbreak in Spain: epizootiological analysis.

RNAs of the most recent foot-and-mouth disease virus isolated in Spain (A5Sp86) during the 1986 outbreak, and of the three vaccine strains in use at that time in that country, have been compared. Although these viruses are serologically indistinguishable, differences have been found among them by T1 fingerprinting. This genetic heterogeneity affects the immunogenic VP1 gene, with amino acid changes located at the carboxyterminal end of the molecule. VP1-coding sequences obtained have been compared with those previously reported for European A5 FMDVs and it has been possible to trace their phylogenetic origin. The most parsimonious evolutionary tree obtained shows that the viruses analyzed are closely related to those previously isolated in 1983 in Spain, Portugal and Morocco. In spite of the VP1 sequence homology shown by this group of viruses, the genetic distances among field isolates and vaccine strains are significantly shorter than the distances found among field isolates. Thus, a significant relationship among virus recovered from recent outbreaks and the vaccine strains in use at that time in Spain, has been obtained.

Amino Acid Sequence↗

PubMed1990

Clinical and electrophysiologic findings in acute ischemic intraHisian bundle-branch block.

Clinical and electrophysiologic features of acute ischemic right bundle-branch block (RBBB) that are reversible by His bundle pacing were analyzed in nine patients. All had large anterior myocardial infarctions (mean peak CK-MB = 185 +/- 71 IU/l), and six showed increased pulmonary capillary pressures. The RBBB occurred within 48 hours of infarction, and in six patients it was associated with left fascicular block. The HV intervals that were measured 1 to 4 days after infarction were normal in all patients. Progression to complete atrioventricular (AV) block occurred in three patients, and one patient required permanent cardiac pacing. Sustained ventricular tachycardia developed in two patients, and ventricular fibrillation developed in five. During a mean follow-up period of 26 months, four patients died (three of them suddenly). The RBBB disappeared in only one case. Acute ischemic intraHisian RBBB occurred in the setting of massive myocardial infarctions complicated by ventricular tachycardia or fibrillation and by a high mortality rate during the follow-up period. The RBBB rarely reverted spontaneously, and the His-Purkinje conduction time was frequently normal.

Bundle of His↗

PubMed1990

On the analysis of viability data: an example with Drosophila.

Larval competition experiments involving two wild type and eight mutant strains of Drosophila melanogaster have been carried out following the substitution procedure proposed by Mather and Caligari (1981). Our main goal has been to compare the competitive abilities of two phenotypically indistinguishable strains (wild and Oregon-R) by means of their responses with eight different mutants. Prior to the analyses of viability data, we have studied the normalizing effect of several transformations in order to determine which was best suited for the analyses. The differences found among the five transformations tested and the untransformed data were not very great. The folded power transformation (Mosteller and Tukey, 1977) was finally chosen. No constant pattern in the responses of the two wild type strains to the mutant competitors was detected. This leads us to conclude that the nature of the competition between the two wild type strains cannot be predicted from a knowledge of their competition with other strains.

Animals↗

PubMed1990

Mitochondrial DNA evolution in experimental populations of Drosophila subobscura.

When two mitochondrial DNA (mtDNA) haplotypes of Drosophila subobscura compete in experimental populations with discrete generations, one or the other approaches fixation, depending on the nuclear background with which they are associated. The approach to fixation, however, is strongly dependent on the effective number of females in the population, Nf. Whether or not the ultimate fate of a given mtDNA haplotype is determined by random genetic drift depends on Nf as well as on the relative fitnesses. Our experimental results show that the mtDNA polymorphisms observed in natural populations are affected by interactions among nuclear polymorphisms, random genetic drift, and direct selection on the mtDNA haplotypes.

Animals↗

PubMed1990

Circadian variations of electrical properties of the heart.

Cardiac refractoriness and electrical inducibility of supraventricular tachycardia (SVT) were assessed at intervals of 1 to 2 hours over a period of 22 hours in 38 patients (25 with paroxysmal SVT). Daily variability of effective refractory period (ERP) had a mean range of 35 +/- 14 mseconds for the atria, 79 +/- 65 mseconds for the AV node, 24 +/- 10 m seconds for the ventricles, 51 +/- 27 mseconds for the retrograde Kent bundle, and 35 +/- 17 mseconds for the antegrade Kent bundle. Between 11 PM and 8 AM there was a significant prolongation of the ERP of the atria (ANOVA, p less than 0.001), AV node (p = 0.002), right ventricle (p less than 0.001), and retrograde Kent bundle (p = 0.005), and a reduction in electrical induction of SVT from 75% to 42% (p less than 0.05) with respect to the first electrophysiologic study. This nocturnal prolongation was preceded by ERP shortening of all explored cardiac sites and by increased tachycardia inducibility between 8 and 10 PM. Six patients with dual AV nodal pathways showed a prolongation of the fast pathway ERP at midnight, whereas conduction through the slow pathway followed an unpredictable daily variability. These data indicate a circadian influence on refractoriness of normal cardiac tissues and accessory pathways that exerted a midnight protection against electrical inducibility of reciprocating tachycardia but a transient arrhythmia facilitation at the evening.

Adolescent↗

PubMed1989

Blood volume and right heart haemodynamics in abrupt hypotension following sublingual isosorbide dinitrate in acute myocardial infarction.

Arterial blood pressure and heart rate were measured in 43 patients with acute myocardial infarction and a systolic blood pressure greater than or equal to 120 mmHg during sublingual administration of 5 mg of isosorbide dinitrate. In 25 of them right heart haemodynamics were also measured. Severe (greater than or equal to 25%) hypotension developed in 12 patients (Group 1, systolic blood pressure 158 +/- 28 to 78 +/- 17 mmHg, mean +/- SD) but not in the remaining 31 (Group 2) and was accompanied by a fall in heart rate (82 +/- 20 to 70 +/- 22 beats min-1, P less than 0.05), in cardiac output (4.3 +/- 0.3 to 3.2 +/- 0.41 min-1, P less than 0.02, n = 5) and in systemic vascular resistances (2326 +/- 463 to 1532 +/- 442 dynes sec-1 cm.5, P less than 0.02) not present in Group 2. The reduction in right (Group 1, 8 +/- 3 to 3 +/- 1, vs. Group 2, 10 +/- 3 to 6 +/- 3 mmHg, P less than 0.005) and in left ventricular filling pressures (Group 1, 15 +/- 4 to 8 +/- 2, vs. Group 2, 18 +/- 6 to 13 +/- 5 mmHg, P less than 0.001) was more remarkable in Group 1. In this group there was also a high incidence of anterior infarction (9/12, 75%).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Sublingual↗