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At least 91 records · Page 5Linked to original sources
PubMed2003

Genome-wide DNA microarray analysis of Francisella tularensis strains demonstrates extensive genetic conservation within the species but identifies regions that are unique to the highly virulent F. tularensis subsp. tularensis.

Francisella tularensis is a potent pathogen and a possible bioterrorism agent. Little is known, however, to explain the molecular basis for its virulence and the distinct differences in virulence found between the four recognized subspecies, F. tularensis subsp. tularensis, F. tularensis subsp. mediasiatica, F. tularensis subsp. holarctica, and F. tularensis subsp. novicida. We developed a DNA microarray based on 1,832 clones from a shotgun library used for sequencing of the highly virulent strain F. tularensis subsp. tularensis Schu S4. This allowed a genome-wide analysis of 27 strains representing all four subspecies. Overall, the microarray analysis confirmed a limited genetic variation within the species F. tularensis, and when the strains were compared, at most 3.7% of the probes showed differential hybridization. Cluster analysis of the hybridization data revealed that the causative agents of type A and type B tularemia, i.e., F. tularensis subsp. tularensis and F. tularensis subsp. holarctica, respectively, formed distinct clusters. Despite marked differences in their virulence and geographical origin, a high degree of genomic similarity between strains of F. tularensis subsp. tularensis and F. tularensis subsp. mediasiatica was apparent. Strains from Japan clustered separately, as did strains of F. tularensis subsp. novicida. Eight regions of difference (RD) 0.6 to 11.5 kb in size, altogether comprising 21 open reading frames, were identified that distinguished strains of the moderately virulent subspecies F. tularensis subsp. holarctica and the highly virulent subspecies F. tularensis subsp. tularensis. One of these regions, RD1, allowed for the first time the development of an F. tularensis-specific PCR assay that discriminates each of the four subspecies.

Bacterial Proteins↗
PubMed1994

Genetic conservation within subtypes in the hepatitis B virus pre-S2 region.

The antigenic determinants for the main hepatitis B virus (HBV) subtypes adw, adr, ayw and ayr lie in the S (surface) polypeptide. Two amino acid residues in particular, encoded by the S gene at codon positions 122 and 160, have been postulated to determine the different antigenic subtypes. In contrast, the 165 nucleotide pre-S2 gene encodes an immunodominant region common to all subtypes that can give rise to neutralizing antibodies. We have characterized the pre-S2 gene sequences of 29 HBV strains of the three main subtypes, adw, ayw and adr. Seven base positions showed variation that was entirely subtype-specific, with six of these variations leading to subtype-specific amino acid differences. This finding affords the possibility of using pre-S2 sequences for genetic subtyping. Two ayw strains from unrelated patients infected in the Middle East had identical pre-S2 sequences with a block of 12 nucleotides deleted. A geographical correlation with subtype observed from serological results was also apparent from phylogenetic analysis of DNA identities within the pre-S2 region. The results support the concept that the main HBV subtypes truly represent families of phylogenetically different strains.

Base Sequence↗
PubMed1989

Lack of expression of HLA-B27 gene in transgenic mouse trophoblast. Conserved genetic pressures underlying extra-embryonic development.

The mechanisms that regulate developmental control of the expression of MHC class I genes during generation of extra-embryonic tissues are largely unknown. In the present study, we studied the levels of transcripts of the human HLA-B27 gene in extra-embryonic tissues of transgenic mice containing the HLA-B27 (heavy chain) gene by in situ hybridization with biotinylated single-stranded RNA probes. In contrast to extra-embryonic stromal cells and embryonic tissues which contain (varying levels of) messenger RNA coding for HLA-B27, specific transcripts were not detected in labyrintho-, or spongiotrophoblast, nor in trophoblastic giant cells. These cells are devoid of HLA A and B locus class I transcripts in man. Regulation of expression of human MHC class I genes in extra-embryonic trophoblast in transgenic animals is thus under conserved selective pressure that is retained across a species barrier. Thus, in extra-embryonic tissues, regulation of expression of MHC class I genes is distinct from the mechanisms operating in developing embryonic cells.

Animals↗
PubMed1993

Antigenic and genetic conservation of the haemagglutinin in H1N1 swine influenza viruses.

We examined the level of antigenic conservation amongst the haemagglutinins (HAs) of H1 swine influenza viruses, recently isolated from a wide geographical area, in haemagglutination inhibition assays against a panel of four monoclonal antibodies (MAbs). We found a high degree of conservation with a dominant variant (52 of 54 isolates) that reacted with all MAbs. Only two minor variants, each failing to react with one MAb, were found. Using a one-step PCR technique followed by direct sequencing of the products, we examined the HA1 region of the HA RNA of two representative dominant variants. We found no amino acid substitutions relative to a reference strain. The sequences of the HA1 RNA of the two minor variants isolated here and of two other minor variants defined previously were also determined. Each contained inferred amino acid substitutions, all located at different positions on the HA. Finally, we sequenced HA1 RNA obtained from the original pig lung suspensions from which the two dominant and two minor variants had been isolated. Three of the parent viruses were identical to their progeny in eggs whereas the fourth parent virus contained four amino acid differences from its progeny.

Antibodies, Monoclonal↗
PubMed1991

Conservation genetics of the koala (Phascolarctos cinereus). II. Limited variability in minisatellite DNA sequences.

We have examined variability in TaqI and EcoRI restriction fragment sizes of DNA from the koala (Phascolarctos cinereus) using six HVR (hypervariable region) probes which reveal complex, individual-specific restriction patterns in humans and other species. Frequency of band-sharing among unrelated koalas was extremely high. This result is likely to be a consequence of the history of near-extinction and artificial recolonization of the populations we have studied, rather than a general marsupial or koala-wide phenomenon.

Animals↗
PubMed1991

Genetic conservation of cyclo-oxygenase.

Homology between sheep and mouse cyclo-oxygenase cDNA and a range of other species was investigated using "zoo blots". Both the sheep and mouse cDNAs showed a high degree of homology to other species. Human cyclooxygenase appears to have greater homology to sheep and other ruminants than to mouse. Both sheep and mouse cDNAs detected identically sized transcripts in human placental total RNA.

Animals↗
PubMedDate not supplied

Two strains of baboon endogenous virus demonstrate a high degree of genetic conservation.

Molecular clones of the baboon endogenous viruses 455K, from Papio anubis, and M7, from Papio cynocephalus, have been constructed from unintegrated viral DNA. Although two specific restriction sites do distinguish the two, detailed restriction maps are nearly identical and heteroduplex molecules show complete homology. The latter observations indicate that this endogenous retrovirus genome has been strongly conserved among different species of baboon.

Animals↗
PubMed1997

Conservation genetics of the koala (Phascolarctos cinereus): low mitochondrial DNA variation amongst southern Australian populations.

Koala (Phascolarctos cinereus) populations in southern Australia have a history of bottlenecks-earlier this century the species became extinct in South Australia, and almost so in Victoria. Subsequently large numbers of animals from island populations (founded from very few animals) have been translocated back to mainland sites and to other islands in the region. As part of a larger study of the genetic structure of koala populations in southern Australia, we have undertaken a survey of mitochondrial DNA restriction fragment length polymorphism (mtDNA-RFLP) variability. Genomic DNA from 91 koalas from five populations was examined using 23 restriction enzymes, and mtDNA fragments were detected using a domestic cat full-length mtDNA clone. Only one of the enzymes, TaqI, revealed polymorphism-a relatively low amount of variation compared with other mammals, although low mtDNA-RFLP variation has also been reported in Queensland koalas. French Island and populations established predominantly from French Island immigrant koalas, either directly or via other island populations, were indistinguishable by haplotype frequencies. The mtDNA data are thus consistent with the interpretation that the koala translocation programme has homogenized gene frequencies amongst those populations involved. South Gippsland is not recorded as having received translocated koalas directly, and has significantly different mtDNA-RFLP haplotype frequencies from all other populations examined. The fact that this distinction was not previously observed in nuclear gene frequencies may reflect predominantly male-mediated dispersal in koalas.

Animals↗
PubMed2001

When does conservation genetics matter?

Is this short review we explore the genetic threats facing declining populations, focusing in particular on empirical studies and the emerging questions they raise. At face value, the two primary threats are slow erosion of genetic variability by drift and short-term lowering of fitness owing to inbreeding depression, of which the latter appears the more potent force. However, the picture is not this simple. Populations that have passed through a severe bottleneck can show a markedly reduced ability to respond to change, particularly in the face of novel challenges. At the same time, several recent studies reveal subtle ways in which species are able to retain more useful genetic variability than they 'should', for example by enhanced reproductive success among the most outbred individuals in a population. Such findings call into question the validity of simple models based on random mating, and emphasize the need for more empirical data aimed at elucidating precisely what happens in natural populations.

Adaptation, Biological↗
PubMed2001

Conservation genetics of peripheral populations of the mygalomorph spider Atypus affinis (Atypidae) in northern Europe.

Genetic diversity and differentiation were studied in peripheral populations of the recently rediscovered purse-web spider Atypus affinis in Denmark and Sweden using allozyme electrophoresis. Because of the very narrow environmental niche exploited by this species, only a limited number of potential habitats are available. Furthermore, fragmentation has reduced the number and size of potential habitats within the last century. The level of genetic diversity in A. affinis was intermediate compared with other nonsocial spiders, but low compared with invertebrates in general. Significant genetic differentiation was found within distances of only 1-10 km with FST estimates ranging from 0.020 to 0.075. Within distances of 30-60 km FST ranged from 0.081 to 0.312. Hierarchical FST revealed that genetic variability was partitioned at 89.8% within populations, 9.5% among populations within regions and only 0.7% among the four main regions in Denmark and Sweden. Comparing the result of the genetic analysis with the life history of A. affinis, it is concluded that the level of successful dispersal is low, and that the species has not recently reinvaded northern Europe but prevailed undiscovered for several decades. Finally, it is suggested that the genetic scenario found for A. affinis might represent that for a wide range of other arthropods with similar life history characteristics.

Animals↗
PubMed2005

Viruses activate a genetically conserved cell death pathway in a unicellular organism.

Given the importance of apoptosis in the pathogenesis of virus infections in mammals, we investigated the possibility that unicellular organisms also respond to viral pathogens by activating programmed cell death. The M1 and M2 killer viruses of Saccharomyces cerevisiae encode pore-forming toxins that were assumed to kill uninfected yeast cells by a nonprogrammed assault. However, we found that yeast persistently infected with these killer viruses induce a programmed suicide pathway in uninfected (nonself) yeast. The M1 virus-encoded K1 toxin is primarily but not solely responsible for triggering the death pathway. Cell death is mediated by the mitochondrial fission factor Dnm1/Drp1, the K+ channel Tok1, and the yeast metacaspase Yca1/Mca1 encoded by the target cell and conserved in mammals. In contrast, cell death is inhibited by yeast Fis1, a pore-forming outer mitochondrial membrane protein. This virus-host relationship in yeast resembles that of pathogenic human viruses that persist in their infected host cells but trigger programmed death of uninfected cells.

Caspases↗
PubMed1994

Modelling problems in conservation genetics using Drosophila: consequences of fluctuating population sizes.

Many natural populations fluctuate widely in population size. This is predicted to reduce effective population size, genetic variation, and reproductive fitness, and to increase inbreeding. The effects of fluctuating population size were examined in small populations of Drosophila melanogaster of the same average size, but maintained using either fluctuating (FPS) or equal (EPS) population sizes. FPS lines were maintained using seven pairs and one pair in alternate generations, and EPS lines with four pairs per generation. Ten replicates of each treatment were maintained. After eight generations, FPS had a higher inbreeding coefficient than EPS (0.60 vs. 0.38), a lower average allozyme heterozygosity (0.068 vs. 0.131), and a much lower relative fitness (0.03 vs. 0.25). Estimates of effective population sizes for FPS and EPS were 3.8 and 7.9 from pedigree inbreeding, and 4.9 vs. 7.1 from changes in average heterozygosities, as compared to theoretical expectations of 3.3 vs. 8.0. Results were generally in accordance with theoretical predictions. Management strategies for populations of rare and endangered species should aim to minimize population fluctuations over generations.

Animals↗