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J R Stringer

Publications and source records attributed to J R Stringer.

At least 37 records · Page 2Linked to original sources
PubMed1998

Genetics, metabolism and host specificity of Pneumocystis carinii.

Pneumocystis carinii is a major cause of severe pneumonia in immunosuppressed individuals, especially in those with human immunodeficiency virus (HIV) infection during their period of progression to acquired immunodeficiency syndrome (AIDS), and constitutes a worldwide problem to public health. Recently, significant advances in the development of experimental animal models of P. carinii infection, as well as in our knowledge of the genetic diversity and taxonomy of P. carinii, have been made. These advances may contribute to our understanding of the transmission of P. carinii pneumonia (PCP) and to the development of new prevention and control strategies. This paper addresses questions relating to the epidemiology of PCP including the detection of the parasite in the environment and in patients, the mechanism of genetic variation of the major surface glycoprotein (MSG) of P. carinii, and host-related genetic variation among isolates of this organism, emphasizing phenotypic expression and its impact on epidemiology and taxonomy.

AIDS-Related Opportunistic Infections↗
PubMed1997

Cell cycle dependence of radiation-induced homologous recombination in cultured monkey cells.

A lacZ transgene recombination system that reports homologous recombination events involving duplicated lacZ segments was used to study recombination in monkey cells exposed to ionizing radiation at different points in the cell cycle. With this system, recombination events can be detected in single cells by histochemical staining soon after exposure of cells to DNA-damaging treatment. Ionizing radiation rapidly induced recombination 5-10-fold in cells that were at the mitosis stage of the cell cycle. Irradiation either of cells at other points in the cell cycle or of nonsynchronized cells had less of an effect on recombination between lacZ segments.

Animals↗
PubMed1997

Residence at the expression site is necessary and sufficient for the transcription of surface antigen genes of Pneumocystis carinii.

The major surface glycoprotein (MSG) of P. carinii f. sp. carinii is a family of proteins encoded by a family of heterogeneous genes. Messenger RNAs encoding different MSG isoforms start with the same sequence, called the upstream conserved sequence (UCS), which is encoded by a single locus. The mechanism by which the UCS becomes part of different MSG mRNAs is not obvious because at least 15 loci, which are distributed throughout the genome, encode MSGs. One possibility is that attachment to the UCS locus is required for the transcription of an MSG gene. The alternative to this expression site model is that mRNAs acquire the UCS by RNA splicing. To distinguish between these two models, UCS/MSG junctions in the genome were compared with UCS/MSG junctions in mRNA. The UCS/MSG junctions in the mRNA matched those in the genome, as would be expected if splicing did not contribute to the attachment of the UCS to the 5' ends of MSG mRNAs. Given that few if any MSG mRNAs lack the UCS, the correspondence between the UCS/MSG junctions in transcripts and those in the genome indicates that attachment to the UCS is both necessary and sufficient for transcription of an MSG gene.

Antigens, Fungal↗
PubMed1997

Sequences of Pneumocystis carinii f. sp. hominis strains associated with recurrent pneumonia vary at multiple loci.

The sequences of the internal transcribed spacer (ITS) of Pneumocystis carinii f. sp. hominis strains from 7 of 15 AIDS patients were found to vary during discrete episodes of P. carinii pneumonia. Changes in the ITS sequence correlated with changes in the mitochondrial large-subunit rRNA sequence. The coincidence of changes in the sequences of the ITS, which is located in the nucleus, with changes in a mitochondrial gene excludes mutation as the cause of the genetic differences between P. carinii f. sp. hominis strains isolated during different episodes of P. carinii pneumonia and supports the hypothesis that recurrent P. carinii pneumonia is caused by reinfection rather than by reactivation of latent organisms. Thus, limiting the exposure of immunocompromised patients to P. carinii f. sp. hominis should help prevent P. carinii pneumonia.

Base Sequence↗
PubMed1997

Identification of porcine Pneumocystis carinii as a genetically distinct organism by DNA amplification.

DNA was amplified from lung samples from three piglets infected with Pneumocystis carinii, using oligonucleotide primers designed to the P. carinii mitochondrial large subunit ribosomal RNA gene. The nucleotide sequence of the amplification product was determined and indicated lack of sequence variation among these pig-derived P. carinii samples at this locus. The data showed that porcine P. carinii was genetically distinct from P. carinii isolated from other mammalian host species.

Animals↗
PubMed1996

Stability of an inverted repeat in a human fibrosarcoma cell.

Deletions and rearrangements of DNA sequences within the genome of human cells result in mutations associated with human disease. We have developed a selection system involving a neo gene containing a DNA sequence inserted into the NcoI site that can be used to quantitatively assay deletion of this sequence from the chromosome. The spontaneous deletion from the neo gene of a 122 bp inverted repeat occurred at a rate of 2.1 x 10(-8) to <3.1 x 10(-9) revertants/cell/generation in three different cell lines. Deletion of the 122 bp inverted repeat occurred between 6 bp flanking direct repeats. Spontaneous deletion of a 122 bp non-palindromic DNA sequence flanked by direct repeats was not observed, indicating a rate of deletion of <3.1 x 10(-9) revertants/cell/generation. This result demonstrates that a 122 bp inverted repeat can exhibit a low level of instability in some locations in the chromosome of a human cell line.

Base Sequence↗
PubMed1996

FLP-mediated site-specific recombination in microinjected murine zygotes.

The FLP recombinase of yeast catalyses site-specific recombination between repeated FLP recombinase target (FRT) elements in yeast and in heterologous systems (Escherichia coli, Drosophila, mosquito and cultured mammalian cells). In this report, it is shown that transient FLP recombinase expression can recombine and activate an extrachromosomal silent reporter gene following coinjection into fertilized one-cell mouse eggs. Furthermore, it is demonstrated that introduction of a FLP-recombinase expression vector into transgenic one-cell fertilized mouse eggs induces a recombination event at a chromosomal FRT target locus. The resulting event occurred at the one-cell stage and deleted a chromosomal tandem array of a FRT containing lacZ expression cassette down to one or two copies. These results demonstrate that the FLP recombinase can be utilized to manipulate the genome of transgenic animals and suggest that FLP recombinase-mediated plasmid-to-chromosome targeting is feasible in microinjected eggs.

Animals↗
PubMed1996

Human placental alkaline phosphatase as a histochemical marker of gene expression in transgenic mice.

The human placental alkaline phosphatase (PLAP) gene was analysed for its utility as a histochemically detectable reporter gene in transgenic mice. A reporter gene was made by linking the PLAP structural gene to an enhancer-promoter element from the human beta-actin gene. This gene was inserted into the mouse genome by transfection of embryonic stem cells, and by microinjection of fertilized eggs. Histochemical staining showed that the transgene was uniformly expressed in four of four stable ES cell lines, and in all ten tissues examined from adult animals from five lines of transgenic mice. Non-transgenic cells did not stain. These results suggest that the human PLAP gene will be of utility in studies requiring phenotypic marking of cells in tissues of mice.

Actins↗
PubMed1996

Pneumocystis carinii telomere repeats are composed of TTAGGG and the subtelomeric sequence contains a gene encoding the major surface glycoprotein.

We have cloned a telomere and adjacent sequences from rat-derived Pneumocystis carinii using the ability of foreign telomeres to complement a yeast artificial chromosome (YAC) deficient by one telomere in Saccharomyces cerevisiae. Characterization of the cloned DNA in the recombinant YAC demonstrated that it was a chimera of two P. carinii sequences, namely a 13.5 kb fragment of mitochondrial DNA and an 8.3 kb distal portion consisting of subtelomeric DNA. The P. carinii telomere repeat was demonstrated to be TTAGGG, the most common telomere repeat found in organisms from the animal and fungal kingdoms. Karyotype analysis confirmed that this sequence was present on all the P. carinii chromosomes. Sequence adjacent to the telomere repeats was shown by Bal31 exonuclease digestion to be located at the chromosome ends. Analysis of the subtelomeric fragment revealed homology to the gene encoding the major surface glycoprotein of P. carinii.

Animals↗
PubMed1996

Translocation of surface antigen genes to a unique telomeric expression site in Pneumocystis carinii.

The surface of Pneumocystis carinii sp. f. carinii contains an antigen known as major surface glycoprotein (MSG), which is encoded by about 100 heterogeneous genes. Expression of MSG genes is not well understood. Previous work identified a sequence termed UCS, which is present at the beginning of nearly all MSG mRNAs, and which is likely to be involved in regulation of MSG gene transcription. Here we show that the UCS was present in one copy per haploid genome, but that different MSG genes were linked to the unique UCS locus in different members of a P. c. carinii population, predicting that individual organisms transcribe a limited number of MSG genes. This prediction was supported by indirect immunofluorescence observations. Comparison of three different populations of P. c. carinii showed that each contained a different set of MSG genes linked to the UCS, suggesting that UCS-MSG junctions are formed by recombination during population growth. Both the UCS and MSG genes were shown to be located at the ends of chromosomes, suggesting that the mechanism for UCS-MSG recombination is reciprocal exchange.

Amino Acid Sequence↗
PubMed1996

Source of Pneumocystis carinii in recurrent episodes of pneumonia in AIDS patients.

OBJECTIVE: To investigate the hypothesis that P.carinii special form hominis (P.c. hominis) reinfections occur in AIDS patients. DESIGN: Polymerase chain reaction (PCR) was used to identify patients who had different P.c. hominis mitochondrial DNA (mtrRNA) genotypes in the two disease episodes (genotype switching). P.c. hominis from these patients were analysed with an allele-specific PCR (ASP) assay to determine whether the genotype found in a second disease episode were present in the first disease episode. To assess the possible contributions of other factors to genotype switching, data on the sampling method and drugs used to treat each patient were compiled. METHODS: Bronchoalveolar lavage fluid (BALF) was subjected to PCR using primers that amplified a 346 base-pair region of the mtrRNA locus known to be polymorphic at site 85 of the amplicon. Samples from patients in whom the P.c. hominis mtrRNA sequence had changed at site 85 in the two disease episodes were studied by ASP in which primers designed to prime synthesis from the allele of the mtrRNA sequence found in second episodes of disease were used in PCR of P.c. hominis DNA from first episodes of P. carinii pneumonia. RESULTS: In four of five patients who produced P.c. hominis with different mtrRNA genotypes during first and second episodes, ASP did not detect the second-episode genotype in first-episode BALF. There was no evidence that either sampling methods or drug-resistance contributed to genotype switching. CONCLUSIONS: P.c. hominis reinfections occur in AIDS patients.

AIDS-Related Opportunistic Infections↗
PubMed1996

Pneumocystis carinii: what is it, exactly?

The identity of Pneumocystis carinii has been uncertain for many years. Until recently, it was widely regarded to be a protozoan because it does not grow in culture and is not susceptible to antifungal drugs. Although these and a number of other phenotypic characteristics of P. carinii differ from those of typical fungi, analysis of DNA sequences has shown that P. carinii is a member of the fungal lineage of eukaryotes. However, a close phylogenetic relative of P. carinii has not yet been found. Analysis of gene sequences has also revealed that P. carinii is not a single entity but that the genus Pneumocystis contains a complex group of organisms. P. carinii organisms from one host species do not grow when introduced into another host species, and P. carinii isolates from different host species are more genetically divergent from one another than might be expected for members of the same species. Genetic variation of a lesser degree also occurs among P. carinii organisms from the same host species, suggesting that it may be possible to identify strains and to conduct transmission and epidemiological studies. Results of early studies exploiting genetic variation among P. carinii isolates from patients have suggested that recurrent P. carinii pneumonia may not always be caused by reactivation of latent organisms, as is commonly believed. However, other features of P. carinii suggest that this microbe has established a long-term relationship with its host. A striking new development in this regard is the discovery of a genetic system that is designed to allow variation in the structure of a major antigen on the surface of P. carinii.

Antigenic Variation↗
PubMed1995

Antigenic variation by positional control of major surface glycoprotein gene expression in Pneumocystis carinii.

Major cell surface glycoproteins (MSGs) of Pneumocystis carinii play a crucial role in host-parasite interactions during P. carinii pneumocystosis in AIDS patients. Genes encoding MSGs are repeated and dispersed throughout the genome and are highly polymorphic. MSG gene expression was found to be mediated by a DNA element that was termed the upstream conserved sequence (UCS). The UCS element maps to a single chromosome, is attached to expressed MSG genes, and encodes the sequence found at the 5' ends of most MSG mRNAs. The UCS is not highly repeated, but P. carinii populations contain many different MSG genes attached to the UCS, suggesting that different organisms in the population have different MSG genes attached to the UCS. Such genetic heterogeneity may be generated by recombination between MSG genes at the UCS locus and one or more of the dozens of MSG genes located elsewhere in the genome.

Animals↗
PubMed1995

Genetic variation among Pneumocystis carinii hominis isolates in recurrent pneumocystosis.

Pneumocystis carinii hominis is a ubiquitous organism that causes pneumonia in immunocompromised persons. Paired P. carinii hominis isolates from human immunodeficiency virus-infected persons who had two episodes of pneumocystosis were examined for genetic heterogeneity. Genetic variation was detected by sequence comparison of a portion of the mitochondrial ribosomal RNA gene. In 5 of 10 patients experiencing two episodes of pneumocystosis, genetically distinct isolates were associated with each episode. These included 4 of 6 patients whose second episode of pneumocytosis occurred > 6 months after their initial bout. The genetic data support the hypothesis that some recurrent episodes of P. carinii hominis pneumonia are caused by reinfection rather than by reactivation of latent infection.

AIDS-Related Opportunistic Infections↗