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Results for “compensatory evolution”

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At least 181 records · Page 10Linked to original sources
PubMed1990

Pressor responsiveness to endothelin is not attenuated in gravid rats.

The aim of this study was to evaluate the effect of synthetic human/porcine endothelin (ET-1) on mean arterial blood pressure (MAP) in pregnant and non-pregnant rats and to compare this to the effects of two well characterized agonists, angiotensin II (AII), and vasopressin (VP). On day 14 of gestation (parturition day 22) polyethylene catheters were chronically implanted in the abdominal aorta for monitoring of MAP and in the vena cava for administration of drugs. Pressor responsiveness was measured in conscious freely moving animals on day 20 and again on the 7th day post-partum. All three agonists increased MAP in a dose related manner. However, whereas the sensitivity of pregnant rats (P) to AII and VP was significantly blunted compared to postpartal (PP) measurements, the MAP responses to ET-1 were the same in both groups. Moreover, the combined administration of ET-1 at a subpressor dose (0.05 pmol/100 g bw) and AII or VP at effective doses significantly potentiated (particularly in P) the pressor effects of AII and VP. These results demonstrate that ET-1 and possibly other vasoactive substances of endothelial origin, override the compensatory mechanism of normal pregnancy with respect to the blunted responsiveness to AII and VP. Such a mechanism may be of particular relevance in the evolution of pregnancy-induced hypertension.

Angiotensin II↗
PubMed1975

Alteration of hepatocytes by subcarcinogenic exposure to n-2-fluorenylacetamide.

These experiments examined the effects of a single, subcarcinogenic dose of dimethylnitrosamine or N-hydroxyfluorenylacetamide when administered after a subcarcinogenic dietary regimen of N-2-fluorenylacetamide. Control rats that received either carcinogen diet alone or a single dose of carcinogen demonstrated neither hepatic nodules nor hepatocellular carcinomas. Those animals that received dimethylnitrosamine subsequent to carcinogen diet demonstrated many persistent hepatic nodules and 100% hepato-cellular carcinomas. These data support the concept that the nodules produced by subcarcinogenic ingestion of N-2-fluorenylacetamide are not composed simply of normal hepatocytes undergoing compensatory regeneration but consist of cells that have been altered by the carcinogen. One manifestation of this alteration is an increased susceptibility to further carcinogenic evolution.

Animals↗
PubMed1996

[The patterns of the karyotypic evolution of cells in culture].

Numerous personal and literary data on the karyotypic variation of cell lines during their establishing and long-term culturing have been reviewed. A new notion about karyotypic evolutionary pathways of cells in culture is presented. A detailed original approach to cytogenetic study of permanent cell lines is given, which allows, via karyotype reconstruction, to obtain finally a new karyotypic characteristics-the generalized reconstructed karyotype (GRK). Application of the cytogenetic approach as a criterion for the control of authenticity, purity and stability of cell lines is discussed. The cell line analysis by means of GRK elicited that the cell line evolution in vitro passes through two stages: a stage of establishment, and a stage of stabilization, both differing in karyotypic variability of cell populations and clonal selection in culture. The data indicate that it is important in experiments to utilize cell lines being in the stage of stabilization and to characterize chromosomally the cell line at the same passage when it is used. Above all, a comparison of karyotypic variations of tumor and leukemic cells in vitro and in vivo has revealed their common karyotypic evolution regularities (a nonrandom character of numerical and structural chromosome changes and the loss of one of the sex chromosomes) and the karyotypic evolutionary regularities characteristic solely of cells in culture. The main of these being a balanced chromosome set in the cell population as a whole and obligatory retention of diploidy in all chromosomes of the normal set by the majority of human and animal cell lines. It has been revealed that no less than two homologs of each autosome are present in cells of at least 85% of examined lines. Other cell lines (at least 15%) of a generally neurogenic origin are shown to be notable by keeping partial or complete monosomies on autosomes throughout the long-term culturing. Peculiarities of the karyotypic evolution of the latter are regarded in detail in addition to the data on the expression of oncogenes and other growth-associated genes in their cells. It is suggested that there are three main compensatory mechanisms through which cell lines with autosomal monosomies may maintain the vitality in culture: polyploidization of initial cell clones, oncogene amplification, mainly of the myc-family oncogenes, and fragmentary or complete extracopying of several autosomes. In summary, perspective of cell line cytogenetics as a field of biology of the cell in culture is discussed.

Animals↗
PubMed2001

Evolution of AZT resistance in HIV-1: the 41-70 intermediate that is not observed in vivo has a replication defect.

The human immunodeficiency virus type 1 (HIV-1) is notorious for its ability to evolve drug-resistance in patients treated with potent antivirals. Resistance to inhibitors of the viral reverse transcriptase (RT) enzyme is frequently mediated by a single amino acid substitution within RT. Resistance against the nucleoside analogue AZT is remarkable in that multiple amino acid changes accumulate over time to yield virus variants with high-level drug resistance. We now report that in addition to drug-resistance properties, the relative replication capacity of the virus variants affects the evolution of AZT resistance. Some of the typical AZT-resistance mutations have a negative impact on virus replication, and the 41-70 double mutant was found to represent a particularly poor virus. Furthermore, introduction of additional AZT-resistance mutations (41-70-215) leads to nearly complete restoration of virus replication. These results may explain the absence of the 41-70 double mutant in clinical samples and indicate that the evolution of AZT resistance is also influenced by virus replication parameters. Prolonged passage of the replication-impaired 41-70 virus in the absence of AZT yielded several fast-replicating variants. These revertants have compensatory changes in the RT polymerase, some of which have been observed previously in AZT-treated patients. Because we could select for these changes without drug pressure, these changes are likely to improve the RT enzyme function and the HIV-1 replication capacity.

Anti-HIV Agents↗
PubMed1991

Secondary structure as a constraint on the evolution of a plant viral satellite RNA.

The genetic variability and evolution of the satellite RNA (satRNA) of cucumber mosaic virus (CMV) was analyzed. Twenty-five CMV-satRNAs compared clustered into three main groups, and no correlation was found between genetic proximity and other characteristics (pathogenicity, geographical origin) of the satRNAs. Values for the number of nucleotide substitutions per site between any two satRNAs suggest that divergence is checked by functional constraints. The analysis of mutations relative to an ancestral sequence, and the number of substitutions per site at first, second and third positions of codons in putative open reading frames, show that the variation of CMV-satRNAs does not follow a pattern typical of coding sequences, and indicates that preservation of the sequence of encoded products is not a constraint to evolution. On the other hand, when the observed variation was analyzed relative to a secondary structure model proposed for CMV-satRNAs, several lines of evidence indicated that the maintenance of the secondary structure is a constraint to evolution: the number of substitutions per site, the number of point insertions and deletions and the number of base substitutions that would disrupt base-pairing were significantly higher for unpaired than for base-paired positions. Also, compensatory mutations at base-paired positions occurred more frequently than expected from random. The results suggest that CMV-satRNAs are non-coding, functional RNAs whose biology would be determined by their direct interaction with components of the host and/or the helper virus.

Base Composition↗
PubMed2000

Effects of environment on compensatory mutations to ameliorate costs of antibiotic resistance.

Most types of antibiotic resistance impose a biological cost on bacterial fitness. These costs can be compensated, usually without loss of resistance, by second-site mutations during the evolution of the resistant bacteria in an experimental host or in a laboratory medium. Different fitness-compensating mutations were selected depending on whether the bacteria evolved through serial passage in mice or in a laboratory medium. This difference in mutation spectra was caused by either a growth condition-specific formation or selection of the compensated mutants. These results suggest that bacterial evolution to reduce the costs of antibiotic resistance can take different trajectories within and outside a host.

Adaptation, Physiological↗
PubMed1996

A simplified T2-T3 thoracoscopic sympathicolysis technique for the treatment of essential hyperhidrosis: short-term results in 100 patients.

A simplified one-time bilateral thoracoscopic T2-T3 sympathicolysis technique using single-lumen endotracheal intubation with high frequency jet ventilation and electrocautery destruction ("sympathicolysis") of the sympathetic ganglia was applied in 100 consecutive patients with severe essential hyperhidrosis (EH). Providing a pleural space can be created, this technique was proven simple and safe, and short-term clinical results were excellent: palmar hyperhidrosis was cured in 98% of patients, and axillar and plantar improvement was achieved in 62 and 65% of patients, respectively. Side-effects and complications were minor (compensatory hyperhidrosis) or self-limiting (pain). These data confirm the safety and efficacy of thoracoscopic sympathetic interventions for the treatment of EH, and support the evolution toward simplified methodologies.

Adolescent↗
PubMed1996

Radiological parameters associated with the evolution of degenerative scoliosis.

The risk factors related to the evolution of the degenerative adult scoliosis are investigated. A review was conducted of the the radiographs of 162 women (mean age 65 years) with degenerative scoliosis who were examined at the Research Center for Diseases of the Musculoskeletal System "Th. Garofalidis" Orthopaedic Department, at the Medical School of Athens University, during the period of 1985 through 1994. Only patients with degenerative lumbar curves greater than 10 degrees and only patients with no previous history of scoliosis were included in the study. The mean follow-up was 8 years (range 5-30 years) and for 30 patients the follow-up period was more than 10 years. The research demonstrated that the degenerative changes of the spine may relate to appearance and evolution of scoliotic curves in adults. Additionally, it was found that the risk factors that are associated with the evolution of the degenerative adult scoliosis are: curves over 30 degrees; curves having Grade II and III rotation; curves that are imbalanced and have a secondary compensatory curve that is sharp and angular at the L4-S1 level; curves in which the apex is at the L2-L3 and L3-L4 area; an intercrest line through the L5 vertebra; and vertebral translation equivalent to or more than 6 mm.

Aged↗
PubMed2006

Epistatic interactions: how strong in disease and evolution?

When the chimpanzee genome sequence was released, human deleterious alleles associated with simple mendelian diseases were observed as wild-type alleles in six genes (AIRE, MKKS, MLH1, MYOC, OTC and PRSS1). The absence of recognizable phenotypic effects in chimpanzee, contrary to the clinical effect observed in humans, is attributed to epistatic interactions (compensation) between potentially deleterious and compensatory alleles. In this report we investigate the possible evolutionary histories by which substitution of alternative variants in these six genes either ameliorates or avoids pathological consequences.

Adaptation, Biological↗
PubMedDate not supplied

[The analysis of monomer sequences in protein and tRNA and the manifestation of the compensation of pathogenic deviations in their evolution].

The sequence analysis of proteins and mitochondrial tRNA indicated that substitutions inducing the pathogenesis in humans often occur in normal individuals of other species having no signs of pathology. The analysis of the structural stability of the protein and tRNA molecules showed that the harmful effect of pathogenic substitutions is often neutralized by other compensatory substitutions, which restore the required normal stability of the structure. A further study of this phenomenon will probably lead to new methods of treatment of genetic pathology, which would be based not on the correction of one substitution but on the correction of the stability of the molecule as an entire functional unit.

Animals↗
PubMed1999

A molecular description of the evolution of resistance.

BACKGROUND: In vitro evolution has been used to obtain nucleic acid molecules with interesting functional properties. The evolution process usually is carried out in a stepwise manner, involving successive rounds of selection, amplification and mutation. Recently, a continuous in vitro evolution system was devised for RNAs that catalyze the ligation of oligonucleotide substrates, allowing the evolution of catalytic function to be studied in real time. RESULTS: Continuous in vitro evolution of an RNA ligase ribozyme was carried out in the presence of a DNA enzyme that was capable of cleaving, and thereby inactivating, the ribozyme. The DNA concentration was increased steadily over 33.5 hours of evolution, reaching a final concentration that would have been sufficient to inactivate the starting population in one second. The evolved population of ribozymes developed resistance to the DNA enzyme, reducing their vulnerability to cleavage by 2000-fold but retaining their own catalytic function. Based on sequencing and kinetic analysis of the ribozymes, two mechanisms are proposed for this resistance. One involves three nucleotide substitutions, together with two compensatory mutations, that alter the site at which the DNA enzyme binds the ribozyme. The other involves enhancement of the ribozyme's ability to bind its own substrate in a way that protects it from cleavage by the DNA enzyme. CONCLUSIONS: The ability to direct the evolution of an enzyme's biochemical properties in response to the behavior of another macromolecule provides insight into the evolution of resistance and may be useful in developing enzymes with novel or enhanced function.

Base Sequence↗
PubMed2002

Experimental and theoretical studies on the excess capacity of Photosystem II.

It has been recently suggested that compensatory changes in Photosystem II (PS II) electron turnover rates can protect photosynthesis from photoinhibition [Behrenfeld et al. (1998) Photosynth Res 58: 259-268]. We have further explored this feature of PS II using a rate electrode for simultaneous measurements of the steady-state rate of oxygen evolution and the oxygen flash yield depending on the background irradiance in both control and photoinhibited algal cells of Chlorella Böhm. Theoretical simulations based on the two-electron gate model agree qualitatively with experimental data if we assume an increase of the electron turnover rate in the remaining functional PS II centers of the photoinhibited sample. Our results confirm the hypothesis that the compensatory effect enables cells to maintain the maximal rates of photosynthesis even in the presence of moderate photoinhibition (decrease of up to 50% in the number of functional centers) and that the effect originates from the inner capacity of electron transport through PS II. The origin of the compensatory effect is briefly discussed.

Journal Article↗
PubMed1997

Site-directed mutations reveal long-range compensatory interactions in the Adh gene of Drosophila melanogaster.

Long-range interactions between the 5' and 3' ends of mRNA molecules have been suggested to play a role in the initiation of translation and the regulation of gene expression. To identify such interactions and to study their molecular evolution, we used phylogenetic analysis to generate a model of mRNA higher-order structure in the Adh transcript of Drosophila melanogaster. This model predicts long-range, tertiary contacts between a region of the protein-encoding sequence just downstream of the start codon and a conserved sequence in the 3' untranslated region (UTR). To further examine the proposed structure, site-directed mutations were generated in vitro in a cloned D. melanogaster Adh gene, and the mutant constructs were introduced into the Drosophila germ line through P-element mediated transformation. Transformants were spectrophotometrically assayed for alcohol dehydrogenase activity. Our results indicate that transformants containing a silent mutation near the start of the protein-encoding sequence show an approximately 15% reduction in alcohol dehydrogenase activity relative to wild-type transformants. This activity can be restored to wild-type levels by a second, compensatory mutation in the 3' UTR. These observations are consistent with a higher-order structure model that includes long-range interactions between the 5' and 3' ends of the Adh mRNA. However, our results do not fit the classical compensatory substitution model because the second mutation by itself (in the 3' UTR) did not show a measurable reduction in gene expression.

Alcohol Dehydrogenase↗
PubMed1976

Functional aspects of hemoglobin evolution in the mammals.

Comparative studies of red cells 2, 3 Diphosphoglycerate (DPG) and its effect on hemoglobin oxygen affinity from a taxonomically diverse set of mammals indicate two anomalous groups: members of the superfamilies Bovoidea (Actiodactyla) and Feloidea (Carnivora). In both taxa all of the individuals assayed had very low or unmeasurable quantities of DPG and red cell lysates with little, if any, DPG effect as measured by the change in oxygen affinity in the absence and presence of the phosphate. However, in both groups compensatory changes have occurred in hemoglobin structure and function so as to reduce the native oxygen affinity and thus cause them to resemble the hemoglobins of DPG-utilizing mammals as they occur in the setting of the red cell. We conclude that this parallelism of function is the result of convergent evolution.

Amino Acid Sequence↗
PubMed2006

Has an aquatic diet been necessary for hominin brain evolution and functional development?

A number of authors have argued that only an aquatic-based diet can provide the necessary quantity of DHA to support the human brain, and that a switch to such a diet early in hominin evolution was critical to human brain evolution. This paper identifies the premises behind this hypothesis and critiques them on the basis of clinical literature. Both tissue levels and certain functions of the developing infant brain are sensitive to extreme variations in the supply of DHA in artificial feeding, and it can be shown that levels in human milk reflect maternal diet. However, both the maternal and infant bodies have mechanisms to store and buffer the supply of DHA, so that functional deficits are generally resolved without compensatory diets. There is no evidence that human diets based on terrestrial food chains with traditional nursing practices fail to provide adequate levels of DHA or other n-3 fatty acids. Consequently, the hypothesis that DHA has been a limiting resource in human brain evolution must be considered to be unsupported.

Adaptation, Physiological↗
PubMed2026

Long-term saline-alkaline selection rewires the growth-survival trade-off in Priestia megaterium.

Saline-alkaline soils impose persistent osmotic, ionic, pH, and nutrient stress on soil microorganisms, but the evolutionary routes by which beneficial bacteria adapt to such conditions remain poorly resolved. We performed adaptive laboratory evolution to examine the adaption of the plant growth-promoting rhizobacterium Priestia megaterium HA22 to long-term oligotrophic saline-alkaline selection. After 175 serial transfers, the evolved lineage proliferated stably at 40 g L-1 Na2SO4 at pH 10.0, whereas the wild-type strain failed to proliferate. Genome resequencing and allelic replacement revealed a 5-bp insertion in spo0A, the master sporulation regulator, as a major adaptive mutation. This mutation abolished sporulation; shortened the lag phase; and enhanced vegetative growth, nutrient uptake, and expression of tricarboxylic acid cycle and nitrogen metabolism gene under saline-alkaline stress. According to untargeted metabolomics, adaptation was accompanied by increased amino acid metabolism and aminoacyl-tRNA biosynthesis, with proline, isoleucine and pantothenic acid functionally promoting growth. A point mutation in ugpB enhanced glycerol-3-phosphate uptake, increased peptidoglycan and wall teichoic acid levels, and partially rescued the survival cost of the spo0A mutation. In greenhouse assays under combined saline-alkaline stress, the evolved strain increased soybean shoot dry weight and root dry weight by 56.08% and 27.02%, respectively. These results indicate that prolonged, predictable saline-alkaline selection can favor active growth rather than dormancy when compensatory cell envelope reinforcement buffers survival costs.

Adaptive laboratory evolution↗
PubMed1990

Comparison of primary and secondary 26S rRNA structures in two Tetrahymena species: evidence for a strong evolutionary and structural constraint in expansion segments.

We have determined the nucleotide sequence of the 26S large subunit (LSU) rRNA genes for two Tetrahymena species, T. thermophila and T. pyriformis. The inferred rRNA sequences are presented in their most probable secondary structures based on compensatory mutations, energy, and conservation criteria. The majority of the nucleotide changes between the two Tetrahymena LSU rRNAs and the positions of a relatively large deletion and of the processing cleavage sites resulting in the generation of the hidden break are all located within the so-called divergent domains or expansion segments. These are regions within the common core of secondary structure where expansions have taken place during the evolution of the rRNA of higher eukaryotes. The dispensable nature of some of the expansion segments has been taken as evidence of their non-functionality. However, our data show that a considerable selective constraint has operated to preserve the secondary structure of these segments. Especially in the case of the D2 and D8 segments, the presence of a considerable number of compensatory base changes suggests that the secondary structure of these regions is of functional importance. Alternatively, these expansion segments may have maintained characteristic folding patterns because only such structures are being tolerated within otherwise functionally important regions.

Animals↗
PubMed2000

Concurrent neutral evolution of mRNA secondary structures and encoded proteins.

Messenger RNA sequences often have to preserve functional secondary structure elements in addition to coding for proteins. We present a statistical analysis of retroviral mRNA which supports the hypothesis that the natural genetic code is adapted to such complementary coding. These sequences are still able to explore efficiently the space of possible proteins by point mutations. This is borne out by the observation that, in stem regions of retroviral mRNA foldings, silent mutations on one strand are preferentially accompanied by conservative mutations on the other. Distances between amino acids based on physicochemical properties are used to quantify the conservation of protein function under the constraint of maintained RNA secondary structure. We find that preservation of RNA secondary structure by compensatory mutations is evolutionary compatible with the efficient search for new variants on the protein level.

Base Sequence↗