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At least 343 records · Page 19Linked to original sources
PubMed1999

Evolution of HLA-class I compared to HLA-class II polymorphism in Terena, a South-American Indian tribe.

We have studied the HLA alleles of 60 unrelated healthy Terena and 10 Terena families. They are members of an isolated Brazilian tribe located in Mato Grosso do Sul (South Central Brazil). Six novel alleles were found in this population: HLA-A*0219 (gf = 0.02), A*0222 (gf = 0.15), HLA-B* 3520 (gf = 0.01), B*3521 (gf = 0.03), B*3912 (gf = 0.03) and B*4803 (gf = 0.16). Five of the six novel alleles differ from their putative progenitors by amino acid replacements in residues that contribute to the pockets of the peptide-binding site. Many of the variants defined by molecular methods were not identified correctly by serological typing. We calculated heterozygosity values (H) for HLA-A, -B, -C, DRB1, DQB1 and DPB . The highest values were observed at the HLA-B locus, followed by HLA-A, -DRB1 and DQB1. Residue positions 9, 24, 45, 62, 67, 95, 114, 116, 156, and 163 of HLA class I showed heterozygosity values greater than 0.50. Nine of them contribute to the peptide-binding specificity pockets and one to the T cell receptor binding site. If HLA antigens are useful for defense against pathogenic agents, heterozygosity would offer an advantage by allowing binding of a larger repertoire of peptides to the class I molecules. Individuals that are heterozygous at these positions would probably have a wider repertoire of peptide presentation to T cells. The observed results including the presence of novel alleles in the class I HLA loci suggest a functionally significant, more rapid evolution of class I compared to class II loci in this South American isolated population.

Alleles↗
PubMed2000

Calcification and measurements of net proton and oxygen flux reveal subcellular domains in Acetabularia acetabulum.

Vegetative adults of Acetabularia acetabulum (L.) Silva were studied as a model system for subcellular patterning in plants, and a description of several phenotypic and physiological characteristics that reveal patterns of subcellular differentiation in this unicellular macroalga was undertaken. Initially, calcification patterns were studied. Under favorable conditions, the rhizoid and most of the stalk calcified. Only the apical 10-20% of the stalk and a small region adjacent to the rhizoid remained uncalcified. Calcification in algae has been reported to result from a biologically mediated local increase in alkalinity. To test this model extracellular pH and extracellular hydrogen ion gradients were examined with ion-selective, self-referencing, electrodes. In the light, A. acetabulum displayed a general pattern of extracellular alkalinity around the entire alga, although in some individuals the region near the rhizoid and the rhizoid itself displayed extracellular acidity. Acetabularia acetabulum also displayed net hydrogen ion influx at the rhizoid and the apical half of the stalk, variable flux in the lower part of the stalk, and net hydrogen ion efflux at the base of the stalk next to the rhizoid. The lack of complete correlation between external pH patterns and calcification suggests that other factors contribute to the control of calcification in this alga. To examine whether net hydrogen ion flux patterns correlated with photosynthetic or respiration patterns, oxygen flux was measured along the stalk using self-referencing O2 electrodes. Photosynthetic oxygen evolution occurred at comparable levels throughout the stalk, with less evolution in the rhizoid. Respiration mainly occurred near and in the rhizoid, with less O2 consumption occurring more apically along the stalk. Our studies of calcification patterns, net hydrogen ion flux and O2 flux revealed several overlapping patterns of subcellular differentiation in A. acetabulum.

Calcification, Physiologic↗
PubMed1999

Phylogenetic analysis among the families of the Cyclophyllidea (Eucestoda) based on comparative morphology, with new hypotheses for co-evolution in vertebrates.

Phylogenetic analysis of the families of the Cyclophyllidea based on comparative morphology revealed support for monophyly of the order. Four equal length trees (CI = 0.71) resulted from analysis of 42 binary and multistate characters. Major conclusions are the following: (1) a basal position for the arostellate groups, with Mesocestoididae + Nematotaeniidae representing the basal subclade; (2) polyphyly for the Anoplocephalidae with sister-group associations postulated respectively for Anoplocephalinae + Thysanosomatinae and Linstowiinae + Inermicapsiferinae; (3) recognition within the rostellate cyclophyllideans of taeniid, dilepidid and davaineid subclades and the Dipylidiidae: (4) designation of Metadilepididae + Paruterinidae as sister taxa; (5) monophyly for the Davaineidae with all inclusive subfamilies; and (6) a close relationship for the Hymenolepididae and acoleate cyclophyllideans. Monophyly for such classically defined groups as the Mesocestoididae, Taeniidae and Davaineidae is corroborated. Polyphyly of the Dilepididae sensu lato, with independence of the Dipylidiidae, Dilepididae sensu Bona (1994), the Metadilepididae + Paruterinidae, and the Gryporhynchidae is confirmed. As presented these constitute testable hypotheses for monophyly and relationships among the families of the Cyclophyllidea. Initial diversification of the cyclophyllideans occurred in mammalian hosts and three independent events of colonisation of avian taxa are postulated. Origins of the cyclophyllideans extend into the Mesozoic or earlier, with extant taxa representing lineages that were persistent across the extinction event that defines the Cretaceous-Tertiary boundary.

Anatomy, Comparative↗
PubMed1990

Extreme differences in charge changes during protein evolution.

The maintenance of a proper distribution of charged amino acid residues might be expected to be an important factor in protein evolution. We therefore compared the inferred changes in charge during the evolution of 43 protein families with the changes expected on the basis of random base substitutions. It was found that certain proteins, like the eye lens crystallins and most histones, display an extreme avoidance of changes in charge. Other proteins, like phospholipase A2 and ferredoxin, apparently have sustained more charged replacements than expected, suggesting a positive selection for changes in charge. Depending on function and structure of a protein, charged residues apparently can be important targets for selective forces in protein evolution. It appears that actual biased codon usage tends to decrease the proportion of charged amino acid replacements. The influence of nonrandomness of mutations is more equivocal. Genes that use the mitochondrial instead of the universal code lower the probability that charge changes will occur in the encoded proteins.

Biological Evolution↗
PubMed1996

Enlarged similarity of nucleic acid sequences.

The concept of nucleic acid sequence base alternations is presented. The number of base alterations for the sequences of different length is established. The definition of "enlarged similarity" of nucleic acids sequences on the basis of sequence base alterations is introduced. Mutual information between sequences is used as a quantitative measure of enlarged similarity for two compared sequences. The method of mutual information calculation is developed considering the correlation of bases in compared sequences. The definitions of correlated similarity and evolution similarity between compared sequences are given. Results of the use of enlarged similarity approach for DNA sequences analysis are discussed.

Base Sequence↗
PubMed1981

Experimental evolution of propanediol oxidoreductase in Escherichia coli. Comparative analysis of the wild-type and mutant enzymes.

A model for the study of experimental evolution is provided by the novel metabolic system responsible for the progressive utilization of L-1,2-propane-diol by mutants of Escherichia coli (strains 3 and 430). In these mutant strains, propanediol oxidoreductase, which serves as L-lactaldehyde reductase in fucose fermentation by wild-type cells, became a key enzyme for aerobic catabolism of propanediol. In the wild-type strain (strain 1), the enzyme is inducible only anaerobically; in strains 3 and 430, the enzyme is synthesized constitutively even in the presence of air. The propanediol oxidoreductase from all three strains was purified to homogeneity by the same procedure. The enzyme of strain 3 clearly differed from that of strain 1 in several respects: Km and V in both directions of the reaction, energy of activation, thermal stability, pH optimum and substrate specificity. However, no difference in any of the above characteristics was found between the enzymes of strains 3 and 430. All three enzymes presented the same electrophoretic mobility. According to immunological data, all three strains differed in their intracellular enzyme level.

Alcohol Oxidoreductases↗
PubMed1997

Evolution and significance of circulating procalcitonin levels compared with IL-6, TNF alpha and endotoxin levels early after thermal injury.

To determine the evolution and significance of circulating procalcitonin (ProCT), IL-6 TNF alpha and endotoxin levels early after thermal injury, we performed a prospective, single unit, longitudinal study. Forty burn patients with total body surface area (TBSA) > 30 per cent were studied, of whom 33 suffered an inhalation injury. Blood samples were taken on the day of admission, every 4 h during the first day and daily during the first week. All patients had increased ProCT and IL-6 levels without any proven infection. Endotoxin and TNF alpha levels remained very low or undetectable. ProCT and IL-levels correlated well with the severity of skin burn injury (respectively, p < 0.006 and p < 0.028, using the non-parametric Kruskal-Wallis test). ProCT levels are not associated with smoke inhalation. ProCT and IL6 are prognostic factors of mortality at the time of admission but less reliable than the clinical UBS (unit burn standard) score. Endotoxin and TNF alpha were undetectable, suggesting that the problem of the early gut bacterial translocation remains to be proven.

Adult↗
PubMed1980

The evolution of human longevity.

In the comparatively short history of human evolution man's lifespan has doubled, posing the question, by what means was this prolongation of life achieved. One line of thought correlates lifespan with oxygen consumption and energy generation, pointing out that small homeothersms which expend energy at a very high rate, are invariable short lived, while animals living more economically in terms of energy expenditure, like some heterotherms and large homeotherms, can attain greatly increased lifespan potentials. The correlation between lifespan and energy expenditure is generally valid, but some animals with low energy needs, notably tropical animals and some lethargic, inactive animals, do not live as long as expected on the basis of the theory. The present paper suggest that the aging process could be accelerated by hyperthermia and the longevity of some homeotherms, beside its connection with energy needs, could also be correlated with the evolution of temperature regulating mechanisms, resulting in more accurate thermal homeostasis. Man's uniquely capacious sweating mechanism, for example, may play a part in the attainment of his long life.

Aging↗
PubMed2000

Zebrafish comparative genomics and the origins of vertebrate chromosomes.

To help understand mechanisms of vertebrate genome evolution, we have compared zebrafish and tetrapod gene maps. It has been suggested that translocations are fixed more frequently than inversions in mammals. Gene maps showed that blocks of conserved syntenies between zebrafish and humans were large, but gene orders were frequently inverted and transposed. This shows that intrachromosomal rearrangements have been fixed more frequently than translocations. Duplicated chromosome segments suggest that a genome duplication occurred in ray-fin phylogeny, and comparative studies suggest that this event happened deep in the ancestry of teleost fish. Consideration of duplicate chromosome segments shows that at least 20% of duplicated gene pairs may be retained from this event. Despite genome duplication, zebrafish and humans have about the same number of chromosomes, and zebrafish chromosomes are mosaically orthologous to several human chromosomes. Is this because of an excess of chromosome fissions in the human lineage or an excess of chromosome fusions in the zebrafish lineage? Comparative analysis suggests that an excess of chromosome fissions in the tetrapod lineage may account for chromosome numbers and provides histories for several human chromosomes.

Animals↗
PubMedDate not supplied

[The late evolution of bronchial asthma appearing in children].

A retrospective study was performed in order to compare the clinical evolution of chronic bronchial asthma with onset in childhood with that of bronchial asthma registered at adult age. The group included 150 cases (87 females and 63 males) out of which 108 (72%) asthma with late onset and 42 (28%) asthma symptoms registered in childhood and adolescence. The symptoms were: allergic rhinitis and spastic tracheobronchitis in 18 (42.8%), dyspneic recurrent bronchitis in 16 (38%), nasal polyposis in 4 (9.5%) and atopic dermatitis in 4 (9.5%) cases. A possible allergic etiology was not taken into consideration in these cases. According to the data obtained, it results that the evolution and the prognosis of bronchial asthma are more severe in patients with its onset in childhood, where there were noted: more severe clinical forms of the disease, higher ventilation dysfunction, more numerous social (family) consequences of the disease, and a higher necessity of long term, systemic corticotherapy than in cases of bronchial asthma with late onset. The delay in the preventive treatment or an incorrect application of it in childhood will condition to a great extent the unfavourable evolution of the disease.

Adrenal Cortex Hormones↗