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At least 703 records · Page 39Linked to original sources
PubMed1998

Comparison of the genetic diversity of wild and captive groups of Microcebus murinus using the random amplified polymorphic DNA method.

Continued survival of most animal species depends on population management and active protection. It is generally agreed that, in order to avoid extinction of endangered species, ex situ and in situ conservation must be developed in tandem. However, even though many recommendations have been put forward to promote the survival of captive populations, some rapidly become extinct due to loss of genetic diversity (drift effect). Genetic markers, such as random amplified polymorphic DNA (RAPD) markers, can be applied to rapid testing of many individuals. They also permit analysis of very small amounts of DNA, when small species such as mouse lemurs (Microcebus) are to be tested. Using RAPD markers, we compare genetic diversity in four captive groups of Microcebus murinus to that in a sample of 70 wild mouse lemurs. Following the principles of Mendelian inheritance, each amplified fragment of DNA may be considered as a 'locus' (or an amplifying site). The series of bands amplified by a particular primer in any individual is referred to as the individual's 'profile'. We tested 5 primers, or, in the above terms, we studied 98 different 'loci'. Results showed that the captive groups had lost genetic information with respect to the wild sample. Among the four captive groups, the loss of genetic diversity varied according to their number of founders and/or the management of their captive reproduction. Our study of polymorphism permitted us to establish tools for the genetic management of captive breeding, and for the determination of paternity which frequently give better results than behavioural studies; and simulation of introductions or departures of individuals in one very monomorphic group permitted estimation of future increases in its genetic diversity.

Amino Acid Sequence↗
PubMed1977

Significance of histocompatibility genes in rheumatology.

Because of the tremendous impact of recent findings of association between genes in the major histocompatibility system and certain rheumatic diseases, the genetics of this system and the methods of analyzing disease association are discussed in detail. These associations represent an important step forward in the search for basic causes and mechanisms of these diseases. Further analyses may permit better classification of diseases and increased understanding of the relationships between genetic and environmental factors in the susceptibility to specific disease.

Antibody Formation↗
PubMed1994

Calcium and neuronal injury in Alzheimer's disease. Contributions of beta-amyloid precursor protein mismetabolism, free radicals, and metabolic compromise.

Alzheimer's disease (AD) is defined by degeneration of specific populations of neurons and the presence of insoluble aggregates of cytoskeletal proteins and amyloid beta-peptide (A beta) within affected brain regions. Alzheimer's disease does not appear to result from a single alteration, but in some cases of inherited AD a specific genetic defect can precipitate the disease. In this article, metabolic compromise, altered metabolism of the beta-amyloid precursor protein (beta APP), and an excitotoxic form of neuronal injury are considered central to the pathogenesis AD. The hypothesis is forwarded that destabilization of neuronal Ca2+ homeostasis underlies neuronal degeneration and that multiple age-associated and/or genetic alterations contribute to the loss of Ca2+ homeostasis. Recent studies showed that the secreted forms of beta APP (APPss) stabilize intracellular free calcium levels ([Ca2+]i) and protect neurons against excitotoxic insults. In contrast, A beta which arises from alternative processing of beta APP forms free radical peptides and aggregates that destabilize [Ca2+]i and make neurons vulnerable to metabolic insults. Increased expression (eg, Down's syndrome) or altered processing (eg, beta APP mutations) of beta APP may increase the A beta/APPs ratio. The death of neurons in AD most likely has an excitotoxic component because: the vulnerable neurons possess high levels of glutamate receptors; experimentally induced excitotoxicity shows several features similar to those of neurofibrillary tangles; and A beta can destabilize [Ca2+]i homeostasis and render neurons vulnerable to neurofibrillary degeneration. Selective vulnerability may result from cell type-specific differences in expression of proteins involved in regulating [Ca+]i. In addition, many intercellular signals are involved in determining whether a neuron is able to maintain [Ca2+]i within a range of concentrations conducive to cell survival and adaptive plasticity. In this regard, it was recently shown that several growth factors can stabilize [Ca]i and protect neurons against excitotoxic injury and A beta toxicity. Age-related changes in the brain (eg, ischemic conditions, reduced glucose uptake, and increased glucocorticoid levels) may compromise the mechanisms that normally regulate [Ca2+]i adaptively.

Aging↗
PubMed2005

Recombination difference between sexes: a role for haploid selection.

Why the autosomal recombination rate differs between female and male meiosis in most species has been a genetic enigma since the early study of meiosis. Some hypotheses have been put forward to explain this widespread phenomenon and, up to now, only one fact has emerged clearly: In species in which meiosis is achiasmate in one sex, it is the heterogametic one. This pattern, known as the Haldane-Huxley rule, is thought to be a side effect, on autosomes, of the suppression of recombination between the sex chromosomes. However, this rule does not hold for heterochiasmate species (i.e., species in which recombination is present in both sexes but varies quantitatively between sexes) and does not apply to species lacking sex chromosomes, such as hermaphroditic plants. In this paper, we show that in plants, heterochiasmy is due to a male-female difference in gametic selection and is not influenced by the presence of heteromorphic sex chromosomes. This finding provides strong empirical support in favour of a population genetic explanation for the evolution of heterochiasmy and, more broadly, for the evolution of sex and recombination.

Animals↗
PubMed2005

Genetic isolation of transport signals directing cell surface expression.

Membrane proteins represent approximately 30% of the proteome in both prokaryotes and eukaryotes. The spatial localization of membrane-bound proteins is often determined by specific sequence motifs that may be regulated in response to physiological changes, such as protein interactions and receptor signalling. Identification of signalling motifs is therefore important for understanding membrane protein expression, function and transport mechanisms. We report a genetic isolation of novel motifs that confer surface expression. Further characterization showed that SWTY, one class of these isolated motifs with homology to previously reported forward transport motifs, has the ability to both override the RKR endoplasmic reticulum localization signal and potentiate steady-state surface expression. The genetically isolated SWTY motif is functionally interchangeable with a known motif in cardiac potassium channels and an identified motif in an HIV coreceptor, and operates by recruiting 14-3-3 proteins. This study expands the repertoire of and enables a screening method for membrane trafficking signals.

14-3-3 Proteins↗
PubMed1991

Susceptibility of captive wildfowl to avian tuberculosis: the importance of genetic and environmental factors.

This study reports the findings of an epidemiological survey of death due to avian tuberculosis in the captive collection of wildfowl at The Wildfowl and Wetlands Trust Centre, Slimbridge, Gloucestershire. Both genetic and environmental factors have been shown to affect the incidence of, and the birds' susceptibility to, the disease. Seasonal body condition was related to the occurrence of death due to the disease in both males and females. Birds from either hot or cold climates appeared to have a higher incidence than those from temperate climates. What the birds ate did not affect incidence but the method they used for obtaining their food did. Higher susceptibility was found in those species evolved for marine or arboreal habitats. Anomalies in susceptibility which suggest a higher level of genetic immunity in some groups have also been found. Reasons are put forward to explain these findings.

Animals↗
PubMed1980

Mutagenicity of antibiotics in microbial assays. Problems of evaluation.

5 antibiotics, 4 of which inhibit protein synthesis in different ways, and 1 of which inhibits bacterial cell-wall synthesis, were tested in a battery of microbial assays for possible genetic effects. All the antibiotics, chloramphenicol, tetracycline, gentamicin, oleandomycin and phosphonomycin induced forward mutation to L-azetidine-2-carboxylic acid resistance in Escherichia coli WP2. This response was closely correlated with the toxic effects and was inferred to be deletion mutation. In addition, chloramphenicol was weakly active in reversion of the frame-shift mutation in Salmonella typhimurium TA98, gentamicin caused petite induction in S. cerevisiae at pH 4.4--4.7 and tetracycline gave a significant reponse with gene conversion and petite induction also in S. cerevisiae but at pH 7.2. The results, particularly those with E. coli, cast doubts on the validity of testing specifically designed antibacterial agents in bacteria, and raise serious problems in the evaluation of such data in terms to human populations.

Animals↗
PubMed1989

Twins, smoking and mortality: a 12-year prospective study of smoking-discordant twin pairs.

Despite the increasing scientific evidence for a causal role of tobacco smoking in lung cancer and coronary heart disease, critics, several decades ago, put forward an alternative hypothesis. The constitutional hypothesis has stated that there are genetic or other common factors, which predispose both to smoking and disease, but that the two are not causally related. A critical test of this hypothesis is the study of disease in monozygotic (MZ) twin pairs in which one smokes and the other never has. Earlier twin studies found only small differences in the mortality of smoking and nonsmoking twins of discordant pairs. In the Finnish Twin Cohort, a population-based panel of adult like-sexed twin pairs, a questionnaire study carried in 1975 permitted identification of twin pairs discordant for cigarette smoking. The nonsmoking cotwins had never been regular smokers. The smoking twins were divided into 1278 current smokers [CS; 143 MZ and 598 dizygotic (DZ) males and 171 MZ and 585 DZ females] and 1210 former smokers (FS; 129 MZ and 408 DZ males and 113 MZ and 341 DZ females). Exposure to tobacco was much higher among males; over 25% of men smoked 20 or more cigarettes daily compared to less than 10% of women. Follow-up of mortality yielded data on time and cause of death. Analyzing on first deaths from concordant pairs, there were 13 deaths in the smokers of male CS MZ pairs and 1 death in the nonsmoking cotwins (relative risk = 13.0, P less than 0.01). Excess mortality was also found for male CS DZ smokers (RR = 2.43, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Comma-free and synchronizable codes.

Shepherd (1981. Proc. natn. Acad. Sci. U.S.A. 78, 1596-1600), Clarke (1982. J. theor. Biol. 99, 397-403), Crick et al. (1976. Origins of Life 7, 389) have put forward the possibility that there was a code, ancestral to the existing genetic code, which was non-degenerate and comma-free. The point of a comma-free code, as first proposed in Crick et al. (1957), is that it provides immunity from frameshift reading errors. In this paper it is argued that if frameshift error immunity is to be used as a selection factor in guiding the search for a hypothetical ancestral code, then the appropriate mathematical formulation of this characteristic is not comma-freeness but synchronizability. The calling card of the comma-free notion is that it results in a limit of 20 on the number of sense codons when applied to the genetic coding system. But so does synchronizability, which includes comma-freeness as a special case. Further, using synchronizability as a constraint instead of comma-freeness yields roughly 3000 times as many potential models for an ancestral code. In particular, the RNY model becomes more compatible with immunity from frameshift error as an evolutionary constraint.

Base Sequence↗
PubMed1990

Cigarette smoking as a cause of lung cancer and coronary heart disease. A study of smoking-discordant twin pairs.

Despite increasing scientific evidence for a causal role of tobacco smoking in lung cancer and coronary heart disease, an alternative hypothesis was put forward several decades ago. The constitutional hypothesis has stated that there are genetic or other common factors, which predispose both to smoking and disease. A critical test of this hypothesis was considered the pattern of occurrence of disease in monozygotic (MZ) twin pairs in which one is a smoker and the other never has been a smoker. Initial twin studies found only small differences in the mortality of smoking and nonsmoking twins of discordant pairs. In the Finnish Twin Cohort, a population-based panel of adult like-sexed twin pairs, a questionnaire study carried out in 1975 permitted identification of 2488 twin pairs discordant for cigarette smoking. Analyses of total mortality and mortality due to coronary heart disease and lung cancer indicate that the smoking members of discordant MZ pairs are at higher risk than their nonsmoking cotwins; increased mortality of smoking cotwins was also found on 21-year follow-up of smoking-discordant pairs in Sweden. Incidence data and noninvasive studies of atherosclerosis in the Finnish sample provide confirmatory evidence for the causal role of smoking in the etiology of coronary heart disease and lung cancer.

Cohort Studies↗
PubMed1996

Inferring frequency dependent selection from the molecular evolution of a rapidly evolving virus: a theoretical investigation.

Hypotheses have been put forward suggesting that immune selection generates much of the intra-patient genetic diversity of rapidly evolving viruses. A Monte Carlo simulation is presented which models sequence evolution in an HIV-like virus under selection from the immune system. Measurements of evolutionary change are then made from the resulting sequences, generating predicted outcomes for each scenario. Frequency dependent immune selection is shown by two statistical measurements to have a significant effect on viral sequence evolution. The use of drawing inferences about underlying evolutionary processes from samples of viral diversity in infected individuals is discussed.

Evolution, Molecular↗
PubMed2004

Protist taxonomy: an ecological perspective.

This is an exploration of contemporary protist taxonomy within an ecological perspective. As it currently stands, the 'morphospecies' does not accommodate the information that might support a truly ecological species concept for the protists. But the 'morphospecies' is merely a first step in erecting a taxonomy of the protists, and it is expected to become more meaningful in the light of genetic, physiological and ecological research in the near future. One possible way forward lies in the recognition that sexual and asexual protists may all be subject to forces of cohesion that result in (DNA) sequence-similarity clusters. A starting point would then be the detection of 'ecotypes'--where genotypic and phenotypic clusters correspond; but for that we need better information regarding the extent of clonality in protists, and better characterization of ecological niches and their boundaries. There is some progress with respect to the latter. Using the example of a community of ciliated protozoa living in the stratified water column of a freshwater pond, it is shown to be possible to gauge the potential of protists to partition their local environment into ecological niches. Around 40 morphospecies can coexist in the superimposed water layers, which presumably represent different ecological niches, but we have yet to discover if these are discrete or continuously variable. It is a myth that taxonomic problems are more severe for protists than for animals and plants. Most of the fundamental problems associated with species concepts (e.g. asexuals, sibling species, phenotypic variation) are distributed across biota in general. The recent history of the status of Pfiesteria provides a model example of an integrated approach to solving what are essentially taxonomic problems.

Animals↗
PubMed2004

Outcomes after renal transplantation for FSGS in children.

Focal segmental glomerulosclerosis (FSGS) is the primary diagnosis resulting in end-stage renal disease in approximately 12% of children receiving renal transplantation. Recurrent FSGS after transplantation is unpredictable and clear risk factors have not been identified. Post-transplantation, the incidence of acute tubular necrosis requiring dialysis is higher in children with FSGS compared with other diagnoses and may represent immediate severe recurrence. Graft survival is decreased in children with FSGS compared with other primary diagnoses, and the impact is greatest in recipients of living donor transplants. Graft loss caused by recurrent FSGS is significantly higher in living donor transplants compared with cadaveric donor transplants in children. Compared with adults, the impact of FSGS on graft survival appears to be greatest in children. White recipient race is associated with a higher risk of graft loss from recurrent FSGS. Efforts to elucidate the mechanisms of recurrent FSGS and to understand risk factors based on genetics, potential circulating cytokines and permeability factors, age and race must move forward before we can significantly impact outcomes in renal transplantation for FSGS.

Age Factors↗
PubMed1983

Mutagenicity and carcinogenicity correlations between bacteria and rodents.

Detection of mutation in bacteria has acquired the status of an accepted procedure in genetic toxicology programs. The methods presently employed in such programs include both forward and reverse mutation-induction techniques in strains of Salmonella typhimurium and Escherichia coli. The specific strains used in these techniques have been selected over the years on the basis of their sensitivity to a broad range of chemical mutagens. In addition, it has been reported that chemical carcinogens can be presumptively identified on the basis of these assays, and bacterial testing has been generally considered the front-line test procedure for the identification of presumptive mutagenic carcinogens. An analysis of correlative studies both retrospective and cross-sectional shows a range of predictive capabilities depending on features such as chemical class, carcinogenic mechanism, and requirements for specific metabolic toxification processes. The greatest limitations associated with the use of bacteria mutation testing is the real and/or perceived issue of the test or a misinterpretation of the correlation coefficients under conditions of routine application. Concerns related to the performance (reliability, reproducibility, and predictability) and relevance of bacteria assays perpetuate controversy surrounding their application to hazard assessment. A review of several studies comparing mutation induction and tumor induction indicates that the Ames test can be useful in screening large numbers of chemicals, but the true correlation coefficient is only about 80% when compared to tumor responses in mice and rats.

Animals↗
PubMed2005

Acquisition of resistance to extended-spectrum cephalosporins by Salmonella enterica subsp. enterica serovar Newport and Escherichia coli in the turkey poult intestinal tract.

Salmonella enterica subsp. enterica serovar Newport resistant to the extended-spectrum cephalosporins (ESCs) and other antimicrobials causes septicemic salmonellosis in humans and animals and is increasingly isolated from humans, animals, foods, and environmental sources. Mechanisms whereby serovar Newport bacteria become resistant to ESCs and other classes of antimicrobials while inhabiting the intestinal tract are not well understood. The present study shows that 25.3% of serovar Newport strains isolated from the turkey poult intestinal tract after the animals were dosed with Escherichia coli harboring a large conjugative plasmid encoding the CMY-2 beta-lactamase and other drug resistance determinants acquired the plasmid and its associated drug resistance genes. The conjugative plasmid containing the cmy-2 gene was transferred not only from the donor E. coli to Salmonella serovar Newport but also to another E. coli serotype present in the intestinal tract. Laboratory studies showed that the plasmid could be readily transferred between serovar Newport and E. coli intestinal isolates. Administration of a single dose of ceftiofur, used to prevent septicemic colibacillosis, to 1-day-old turkeys did not result in the isolation of ceftiofur-resistant E. coli or Salmonella serovar Newport. There was a remarkable association between serotype, drug resistance, and plasmid profile among the E. coli strains isolated from the poults. This study shows that Salmonella serovar Newport can become resistant to ESCs and other antibiotics by acquiring a conjugative drug resistance plasmid from E. coli in the intestines.

Animals↗