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C A Strathdee

Publications and source records attributed to C A Strathdee.

At least 19 recordsLinked to original sources
PubMed2001

Synergy between tetA and rpsL provides high-stringency positive and negative selection in bacterial artificial chromosome vectors.

Bacterial artificial chromosome (bacmid) vectors are used to stably propagate large, complex fragments of cloned DNA and are a core technology for functional genomics. The simplest method of analyzing bacmid clones would involve a direct mutagenesis or allele exchange protocol utilizing positive and negative selectable markers. The utility of three different negative selectable markers to function in the context of a bacmid vector was therefore investigated: sacB from Bacillus subtilis, which confers sensitivity to sucrose; tetA from TN10, which confers resistance to tetracycline, osmotic sensitivity, and sensitivity to kanamycin and streptomycin; and rpsL from Escherichia coli, which confers sensitivity to streptomycin. When expressed individually in the context of a bacmid vector, each of these markers confers a similar stringency of negative selection, with plating efficiencies on selective media of 2.3 x 10(-5), 9.4 x 10(-4), and 5.7 x 10(-5), respectively. However coexpression of rpsL and tetA results in a synergistic enhancement of the osmotic, kanamycin, and streptomycin sensitivities, with a stringency of selection of approximately 50- to approximately 1000-fold over that obtained with rpsL or tetA alone and approximately 20-fold more than that obtained using sacB. The combination of rpsL and tetA thus serves as the most efficient positive and negative selectable marker system described to date.

Antiporters↗
PubMed2000

Disease-associated mutations in SOD1 are impervious to dominant positive or negative effects.

The familial form of amyotrophic lateral sclerosis is caused by mutations in the SOD1 gene encoding the cytosolic antioxidant enzyme Cu,Zn superoxide dismutase. Although there is no clear correlation between disease and dismutating catalytic activity among the various disease-associated SOD1 alleles, all of the known missense mutations significantly alter the half-life of the encoded polypeptides. Using transient transfection studies in mammalian cells, it was demonstrated that a frameshift mutation in SOD1 which results in a truncated polypeptide is similarly destabilized. Using an epitope-tagging strategy to discriminate between mutant and wild-type SOD1 polypeptides, no evidence for dominant effects on polypeptide stability was detected, including that of a positive effect of the wild-type on mutant SOD1 polypeptides or that of a negative effect of mutant on wild-type SOD1 polypeptides. These experiments thus favor a non-catalytic role of mutant forms of SOD1 in disease progression.

5' Untranslated Regions↗
PubMed2000

Expression of the tetA(C) tetracycline efflux pump in Escherichia coli confers osmotic sensitivity.

Expression of tetA(C) in Escherichia coli confers resistance to tetracycline as well as sensitivity to nickel and cadmium salts, lipophilic chelating agents, and aminoglycoside antibiotics. In this report we determine that high-level expression of tetA(C) also confers an osmotic sensitivity. The osmotic-sensitive phenotype is distinct from the tetracycline-resistant phenotype and can be localized to a domain contained within the first 98 amino acid residues of the TetA(C) polypeptide.

Antiporters↗
PubMed2000

Biolistic-mediated interleukin 4 gene transfer prevents the onset of type 1 diabetes.

We tested the efficacy of biolistic-mediated gene transfer as a noninvasive therapy for type 1 diabetes (T1D) in nonobese diabetic (NOD) mice by expression of murine interleukin 4 (mIL-4) cDNA. Epidermal delivery of 2 microg of DNA yielded transient detection of serum mIL-4, using a conventional cDNA expression vector. A vector stabilized by incorporation of the Epstein-Barr virus (EBV) EBNA1/oriP episomal maintenance replicon produced higher levels of serum mIL-4 that persisted for 12 days after inoculation. Although biolistic inoculation of either vector reduced insulitis and prevented diabetes, the protracted mIL-4 expression afforded by the EBV vector resulted in Th2-type responses in the periphery and pancreas and more significant protection from the onset of diabetes. Our studies demonstrate the efficacy of biolistic gene delivery of stabilized cytokine expression as a viable therapeutic approach to prevent the onset of T1D.

Animals↗
PubMed2000

The inhibitory function of CTLA-4 does not require its tyrosine phosphorylation.

CTLA-4 is a negative regulator of T cell responses. Sequence analysis of this molecule reveals the presence of two cytoplasmic tyrosine residues at positions 165 and 182 that are potential Src homology (SH)-2 domain binding sites. The role of phosphorylation of these residues in CTLA-4-mediated signaling is unknown. Here, we show that sole TCR ligation induces zeta-associated protein (ZAP)-70-dependent tyrosine phosphorylation of CTLA-4 that is important for cell surface retention of this molecule. However, CTLA-4 tyrosine phosphorylation is not required for down-regulation of T cell activation following CD3-CTLA-4 coengagement. Specifically, inhibition of extracellular signal-regulated kinase (ERK) activation and of IL-2 production by CTLA-4-mediated signaling occurs in T cells expressing mutant CTLA-4 molecules lacking the cytoplasmic tyrosine residues, and in lck-deficient or ZAP-70-deficient T cells. Therefore, CTLA-4 function involves interplay between two different levels of regulation: phosphotyrosine-dependent cell surface retention and phosphotyrosine-independent association with signaling molecules.

Abatacept↗
PubMed2000

A modular set of helper-dependent herpes simplex virus expression vectors.

Herpes simplex virus (HSV) has many favorable properties in terms of its potential to serve as a delivery and expression platform for gene-based therapies, including the ability to establish persistent infections, a broad tissue tropism, episomal maintenance of transduced genes, and a large genome that can incorporate many additional cDNAs. Helper-dependent HSV vectors (commonly known as HSV amplicons) are well positioned to exploit the biology of the virus, since they contain only the two cis elements required for HSV replication and packaging and thus do not require the silencing of any viral genes to prevent toxicity to transduced cells over the course of cDNA expression. In this report we describe the development of a set of modular HSV amplicon vectors that can easily be modified to incorporate different genetic elements or alternatively can be used to retrofit existing expression constructs such that they can be packaged into infectious HSV particles.

Animals↗
PubMed2000

Herpes simplex viral and amplicon vector-mediated gene transfer into glia and neurons in organotypic spinal cord and dorsal root ganglion cultures.

The progression of neurodegenerative diseases and secondary consequences of spinal cord injury may be diminished by introducing transgenes to glia, spinal neurons, and/or sensory neurons. Organotypic cultures of spinal cord slices and dorsal root ganglia proved to be an excellent system in which to compare the relative neurotropism of a replication-defective recombinant herpes simplex virus and herpes virus-derived amplicon vectors. Hundreds of beta-galactosidase-expressing cells, transduced by the viral vectors, were observed in spinal cord slices 3 and 8 days postinfection. Immunostaining to identify the infected cell type indicated that oligodendrocytes were permissive for viral vector transduction of beta-galactosidase in the spinal cord slice, whereas neurons were not. Heparan sulfate proteoglycan, the initial receptor for herpes contact with cells, was highly expressed in the white matter of the spinal cord slice, but was negligible in the gray matter. In contrast to the spinal cord, many fewer cells were infected in the dorsal root ganglia (DRG) by these vectors, but a majority of infected cells were identified as sensory neurons. Heparan sulfate proteoglycan expression was abundant in the sensory fibers emanating from the DRG and also surrounded each neuron within the ganglion. Our results demonstrate HSV-induced transgene expression that is amenable to ex vivo assessment of its physiological impact.

Animals↗
PubMed1999

Efficient control of tetracycline-responsive gene expression from an autoregulated bi-directional expression vector.

The tetracycline-responsive expression system is based on the ability of the chimeric tTA and rtTA transactivators to stimulate specifically transcription from a companion synthetic CMV* or TK* promoter element, and can provide tightly regulated gene expression that can be induced up to five orders of magnitude in cultured cells and transgenic mice. A major problem with the system is that high level expression of the tTA or rtTA transactivators causes cellular toxicity. Under conditions of prolonged expression this results in selective pressure against the stable incorporation of vectors expressing the tTA or rtTA transactivators, and makes the generation of stable cell lines and transgenic mice problematic. In this report we describe the development of a set of autoregulated bi-directional expression vectors in which the weaker TK* promoter is used to direct expression of the rtTA or tTA transactivator and the stronger CMV* element is used to direct cDNA expression. In this format the transactivator and response elements are encoded on the same vector, which simplifies the system and ensures that gene expression is effectively skewed in favor of the cDNA while maintaining a continuously low level of transactivator expression. We find that such an autoregulated system works equally well for both the tTA and rtTA transactivators, provided that they contain a nuclear localization signal. Similar to other versions of the tetracycline-responsive expression system, gene expression is tightly regulated and can be efficiently switched between the off and on expression states by doxycycline. In contrast with other tetracycline-responsive systems, however, expression of the rtTA and tTA transactivators from the autoregulated TK* promoter is low enough such that there is no cellular toxicity associated with either expression state. By incorporating a selectable marker into these vectors, all of the components required for using the system are now contained on a single plasmid construct, and we find that this format provides a more reliable and greatly simplified method for the generation of stable cell lines.

Cell Line↗
PubMed1998

An enhanced packaging system for helper-dependent herpes simplex virus vectors.

Helper-dependent herpes simplex virus (HSV) vectors (amplicons) show considerable promise to provide for long-term transduced-gene expression in most cell types. The current packaging system of choice for these vectors involves cotransfection with a set of five overlapping cosmids that encode the full HSV type 1 (HSV-1) helper virus genome from which the packaging (pac) elements have been deleted. Although both the helper virus and the HSV amplicon can replicate, only the latter is packaged into infectious viral particles. Since the titers obtained are too low for practical application, an enhanced second-generation packaging system was developed by modifying both the helper virus and the HSV amplicon vector. The helper virus was reverse engineered by using the original five cosmids to generate a single HSV-bacterial artificial chromosome (BAC) clone in Escherichia coli from which the pac elements were deleted to generate a replication-proficient but packaging-defective HSV-1 genome. The HSV amplicon was modified to contain the simian virus 40 origin of replication, which acts as an HSV-independent replicon to provide for the replicative expansion of the vector. The HSV amplicon is packaged into infectious particles by cotransfection with the HSV-BAC helper virus into the 293T cell line, and the resulting cell lysate is free of detectable helper virus contamination. The combination of both modifications to the original packaging system affords an eightfold increase in the packaged-vector yield.

Animals↗
PubMed1995

Identification of epidemiologic markers for Neisseria meningitidis using difference analysis.

The feasibility of identifying epidemiologic markers based solely on the identification of DNA fragments present in outbreak-associated isolates was investigated using Neisseria meningitidis (Nm) as a model system. The clonal structure of Nm has been well characterized using multilocus electrophoresis. In Canada, electrophoretic types ET1, ET5, ET9 and ET21 are being displaced from the natural population by type ET15, and the latter type is associated with an increased prevalence of serogroup C meningococcal disease. Difference analysis, which uses subtractive hybridization and polymerase chain reaction (PCR) amplification, was employed to identify amplifiable DNA fragments (amplicons) that differ between the ET15 and the ET1, ET5, ET9 and ET21 genomes. 14 amplicons were cloned which were further characterized by Southern blot analysis to identify six amplicons that represent fragments either unique to or highly polymorphic in the ET15 genome. Oligodeoxyribonucleotide primer pairs were designed for each of the six amplicons, and PCR amplification was used to determine their prevalence across a panel of 167 Nm isolates representative of other serogroups and ETs. Among group C isolates only two of the six amplicons, designated as A and G, were effective in discriminating ET15 from non-ET15 isolates. Amplicon A detects a deletion in the dhps gene which effectively differentiates sulfonamide-sensitive and -resistant serogroup C isolates. The frequency of amplicon A and G detection in the other serogroups and ETs was too great to facilitate their direct use as diagnostic markers for the differentiation of virulent Nm isolates.

Bacterial Outer Membrane Proteins↗
PubMed1995

Oligonucleotide primers designed to differentiate pathogenic pseudomonads on the basis of the sequencing of genes coding for 16S-23S rRNA internal transcribed spacers.

Universal primers targeting conserved sequences flanking the 3' end of the 16S and the 5' end of the 23S rRNA genes (rDNAs) were used to amplify the 16S-23S rDNA internal transcribed spacers (ITS) from eight species of pseudomonads which have been associated with human infections. Amplicons from reference strains of Pseudomonas aeruginosa, Pseudomonas cepacia, Pseudomonas gladioli, Pseudomonas mallei, Pseudomonas mendocina, Pseudomonas pickettii, Pseudomonas pseudomallei, and Xanthomonas maltophilia were cloned from each species, and sequence analysis revealed a total of 19 distinct ITS regions, each defining a unique sequevar with ITS sizes ranging from 394 (P. cepacia) to 641 (P. pseudomallei) bp. Five distinct ITS sequevars in P. cepacia, four in P. mendocina, three in P. aeruginosa, two each in P. gladioli and P. pseudomallei, and one each in P. mallei, P. pickettii, and X. maltophilia were identified. With the exception of one P. cepacia ITS, all ITS regions contained potential tRNA sequences for isoleucine and/or alanine. On the basis of these ITS sequence data, species-specific oligonucleotide primers were designed to differentiate P. aeruginosa, P. cepacia, and P. pickettii. The specificities of these primers were investigated by testing 220 clinical isolates, including 101 strains of P. aeruginosa, 103 strains of P. cepacia, and 16 strains of P. pickettii, in addition to 24 American Type Culture Collection (ATCC) Pseudomonas strains. The results showed that single primer pairs directed at particular ITSs were capable of specifically identifying the ATCC reference strains and all of the clinical isolates of P. aeruginosa and P. pickettii, but this was not the case with several ITS-based primer pairs tested for P. cepacia. This pathogen, on the other hand, could be specifically identified by primer pairs directed against the 23S rDNA.

Base Sequence↗
PubMed1993

Genomic fingerprinting of Neisseria meningitidis associated with group C meningococcal disease in Canada.

A single electrophoretic type (ET15) of Neisseria meningitidis has been associated with an increased incidence of group C meningococcal disease in Canada. Genomic fingerprinting through pulsed-field gel electrophoresis of chromosomal DNA was used to characterize the clonal relationship among meningococcal isolates of different electrophoretic types and among isolates within ET15. The genomic fingerprints of the ET15 isolates, while similar as a group, were sufficiently distinct to confirm linkage for four pairs of strains from focal outbreaks and differed markedly from those of the other common electrophoretic types, ET5, ET9, and ET21.

Canada↗
PubMed1992

Cloning of cDNAs for Fanconi's anaemia by functional complementation.

Fanconi's anaemia is a rare autosomal recessive disorder characterized by progressive pancytopaenia and a cellular hypersensitivity to DNA crosslinking agents. Four genetic complementation groups have been identified so far, and here we use a functional complementation method to clone complementary DNAs that correct the defect of group C cells. The cDNAs encode alternatively processed transcripts of a new gene, designated FACC, which is mutated in group C patients. The predicted FACC polypeptide does not contain any motifs common to other proteins and so represents a new gene involved in the cellular response to DNA damage.

Amino Acid Sequence↗
PubMed1992

Evidence for at least four Fanconi anaemia genes including FACC on chromosome 9.

Fanconi anaemia (FA) is a DNA repair disorder characterized by cellular hypersensitivity to DNA cross-linking agents and extensive phenotypic heterogeneity. To determine the extent of genetic heterogeneity present in FA, a panel of somatic cell hybrids was constructed using polyethylene glycol-mediated cell fusion. Three new complementation groups were identified, designated FA(B), FA(C) and FA(D), and the gene defective in FA(C) which we have recently cloned was localized to chromosome 9q22.3 through in situ hybridization. These results suggest that mutations in at least four different genes lead to FA, a degree of genetic heterogeneity comparable to that of other DNA repair disorders.

Chromosome Mapping↗