Biomedical subjects
S D Brown
Publications and source records attributed to S D Brown.
Structure of the Drosophila DNA topoisomerase I gene and expression of messages with different lengths in the 3' untranslated region.
The nucleotide sequence of the Drosophila DNA topoisomerase I gene (top1) has been determined. Structurally, top1 consists of eight exons and seven introns. The top1 coding region contains a new class of opa repeats, encoding clusters of serine residues instead of glutamine repeats usually seen in Drosophila genes of the neurogenic loci. A unique feature of top1 is the developmental switch of its transcripts: a heterogeneous population of transcripts ranging from 3.8 to 4.2kb seen maximally at 0-2h of embryogenesis and a 5.2-kb transcript maximal at 6-12h of embryonic development. The transcripts expressed in the 0-2-h embryo have been shown as maternal storage products specific to ovarian tissues. RACE analysis shows that whereas the 6-12-h transcripts have a single site for polyadenylation, there are at least 12 different sites for poly(A) addition to the 0-2-h transcripts. An additional intron specific for the maternal storage transcripts appears in some of the 0-2-h transcripts. No significant heterogeneity at the 5' end of the top1 transcripts is seen. Sequence searches have revealed a number of regulatory sequences for potential translational control in the 3' untranslated region.
Mapping of the human and murine X11-like genes (APBA2 and apba2), the murine Fe65 gene (Apbb1), and the human Fe65-like gene (APBB2): genes encoding phosphotyrosine-binding domain proteins that interact with the Alzheimer's disease amyloid precursor protein.
Explore the source record for details and available documents.
Multicenter survey of the in vitro activity of four expanded-spectrum beta-lactams against consecutive contemporary clinical isolates.
A survey of the in vitro susceptibility of consecutive clinical bacterial isolates to cefotaxime, ceftazidime, cefpodoxime, and aztreonam was conducted at 10 North American medical centers during the first quarter of 1997. All four drugs had good activity against Enterobacteriaceae and fastidious Gram-negative bacteria and poor activity against enterococci and methicillin-resistant staphylococci. No significant trends in susceptibility to cefotaxime or ceftazidime were observed when compared with a previous similar survey. The use of cefpodoxime MIC > 2.0 micrograms/mL as a marker for extended-spectrum beta-lactamase production by Escherichia coli and Klebsiella spp. had good sensitivity, but the specificity was very poor for E. coli. Thus, at least for E. coli, this screening test seems to be of questionable value unless used to indicate the need for additional tests such as clavulanic acid inhibition. Disk diffusion zone diameters correlated well with the MICs for all four drugs and support the current interpretive criteria.
Mouse models of genetic disease: new approaches, new paradigms.
The mouse mutant resource is a valuable tool for gene function studies in the post-genomics era. However, despite a seemingly large catalogue of mouse mutants, it is recognized that we have access to mutations at only a small fraction of the total number of mouse genes. There is a phenotype gap that needs to be narrowed by the implementation of large-scale, systematic mutagenesis programmes in the mouse. Both genotype-driven and phenotype-driven approaches can be employed to recover new mouse mutations. Genotype-driven approaches include large-scale genome-wide mutagenesis by gene trapping in embryonic stem cells. For genotype-driven approaches, the initial focus is on the characterization of the mutational change to the genome. Identification of the mutated gene is relatively trivial, but the genotype-driven route provides little indication of the likely phenotypic outcome of the mutation. In contrast, phenotype-driven approaches employ mutagenesis procedures that emphasize the recovery of novel phenotypes without prior assumptions about the underlying gene or pathway that has been disrupted--although identifying the underlying gene may not be trivial. One phenotype-driven approach includes chemical mutagenesis using N-ethyl-N-nitrosourea (ENU). ENU mutagenesis programmes are increasingly being brought to bear on increasing the breadth and depth of the mouse mutant resource, and in so doing narrowing the phenotype gap.
Mutations in the myosin VIIA gene cause a wide phenotypic spectrum, including atypical Usher syndrome.
Explore the source record for details and available documents.
Mouse mutagenesis-systematic studies of mammalian gene function.
The mouse will play a pivotal role in mammalian gene function studies as we enter the post-genomics era. The challenge is to develop systematic, genome-wide mutagenesis approaches to the study of gene function. The current mouse mutant resource has been an important source of human genetic disease models. However, despite an apparently large catalogue of mouse mutations, we have access to mutations at only a small fraction of the likely total number of mammalian genes-there is a phenotype gap that needs to be filled by the establishment of new mutagenesis programmes. Two routes, genotype- and phenotype-driven, can be used for the recovery of novel mouse mutations. For the former, gene trap embryonic stem cell libraries appear set to deliver a large number of mutations around the mouse genome. The advantage of genotype-driven approaches is the ease of identification of the mutated locus; the disadvantage that a priori assumptions have to be made concerning the function and likely phenotype of the mutated gene. In contrast, phenotype-driven mutagenesis emphasizes the recovery of novel phenotypes. One phenotype-driven approach that will play an important role in expanding the mouse mutant resource employs the mutagen N-ethyl-N-nitrosourea (ENU). The phenotype-driven route makes no assumptions about the underlying genes involved, and ENU mutagenesis programmes can be expected to play a significant role in uncovering novel pathways and genes; the disadvantage is that the identification of the mutant gene is still not trivial. Together, the complementary routes of genotype- and phenotype-driven mutagenesis will provide a much enlarged catalogue of mouse mutations and phenotypes for future gene function studies.
Susceptibility to RPR 106,972, quinupristin/dalfopristin and erythromycin among recent clinical isolates of enterococci, staphylococci and streptococci from North American medical centres.
An orally administered streptogramin (RPR 106,972) and a parenteral streptogramin (quinupristin/dalfopristin) were evaluated against a collection of 2481 recent clinical isolates of gram-positive cocci. The isolates were gathered from ten North American medical centres during the winter months of 1996-1997. In spite of minor differences, both streptogramins had essentially identical spectra of activity which included many erythromycin-resistant isolates. Previously proposed interpretative criteria for quinupristin/dalfopristin disc diffusion susceptibility tests were confirmed.
Comparison of brain temperature with bladder and rectal temperatures in adults with severe head injury.
OBJECTIVE: The purpose of this study was to compare brain temperature (Tbr) with conventional indicators of core body temperature (i.e., rectal temperature [Tre] and bladder temperature [Tbl]), in adults with severe head injury. METHODS: The relationships between Tbr and Tbl and between Tbr and Tre are described in terms of differences in temperature in eight patients with severe head injury. INSTRUMENTATION: Brain tissue temperature was measured every minute, with a thermocouple embedded 2 cm from the tip of a ventriculostomy catheter used to measure intracranial pressure. Tbl was measured with a thermistor embedded in a bladder catheter, and Tre was measured with a thermistor in a rectal probe. RESULTS: Tbr was usually greater than Tbl and Tre. The average difference between Tbr and Tbl for each patient ranged from 0.32 to 1.9 degrees C, with standard deviations of the difference ranging from 0.30 to 0.80 degrees C. The average difference between Tbr and Tre for each patient ranged from 0.1 to 2.0 degrees C, with standard deviations of the difference ranging from 0.32 to 1.08 degrees C. In the majority of patients, the differences (Tbr - Tbl and Tbr - Tre) were greater at temperatures outside of the normal temperature range (Tbr < or =36 degrees C and >38 degrees C). CONCLUSION: Tbl and Tre often underrepresent Tbr after traumatic brain injury, particularly when the patient is hypo- or hyperthermic.
A high-resolution microsatellite map of the mouse genome.
The European Collaborative Interspecific Backcross (EUCIB) resource was constructed for the purposes of high-resolution genetic mapping of the mouse genome (). The large Mus spretus/C57BL/6 backcross of 982 progeny has a genetic resolution of 0.3 cM at the 95% confidence level ( approximately 500 kb in the mouse genome). We have used the EUCIB mapping resource to develop a genome-wide high-resolution genetic map incorporating 3368 microsatellites. The microsatellites are distributed among 2302 genetically separated bins with 1.46 markers per bin on average. Average bin separation is 0.61 cM. This high-resolution genetic map will aid the construction of a robust physical map of the mouse genome.
PMX-622 (polymyxin B-dextran 70) does not alter in vitro activities of 11 antimicrobial agents.
Because of its capacity to neutralize the lethality of gram-negative bacterial endotoxic lipopolysaccharides, PMX-622 (polymyxin B bound to dextran 70) is being developed for possible adjunctive therapy of gram-negative sepsis. In this study, it was determined that the in vitro antimicrobial activity of PMX-622 was minimal and that it does not interfere with the in vitro antimicrobial activity of 11 antibiotics commonly used to treat gram-negative infections.
Antipneumococcal activities of a ketolide (HMR 3647), a streptogramin (quinupristin-dalfopristin), a macrolide (erythromycin), and a lincosamide (clindamycin).
Four different compounds belonging to the macrolide-lincosamide-streptogramin B (MLSb) class of antimicrobial agents were tested against 611 Streptococcus pneumoniae strains. The ketolide (HMR 3647, previously RU66647) and the streptogramin (quinupristin-dalfopristin) were both active against pneumococci with high-level MLSb resistance (clindamycin-resistant strains) as well as those with low-level macrolide resistance (clindamycin-susceptible strains).
In vitro antimicrobial activity of MSI-78, a magainin analog.
MSI-78 is a cationic peptide with broad-spectrum antimicrobial activity and is being developed as a topical agent. We compared the in vitro activity of MSI-78 with those of ofloxacin and other antibiotics against fresh clinical isolates. Based on MIC distribution statistics, strains for which the MSI-78 MIC was < or = 64 micro/ml were assumed to be susceptible for purposes of this report. Of 411 aerobic isolates tested, 91% were susceptible to MSI-78, compared to 91% for ofloxacin and 92% for ciprofloxacin. Only enterococci consistently required > or = 64 microg of MSI-78/ml for inhibition. MSI-78 demonstrated bactericidal activity equivalent to that of ofloxacin. Of 61 anaerobes, 97% were susceptible to MSI-78. Of 10 isolates of Candida albicans, 3 were inhibited by MSI-78 at 24 h. Further studies of this compound appear to be warranted.
In vitro activities of clinafloxacin against contemporary clinical bacterial isolates from 10 North American centers.
Clinafloxacin was more active than ciprofloxacin against 4,213 aerobic and facultative anaerobic bacterial isolates from 10 medical centers, as tested by broth microdilution and disk diffusion methods. The percentage of 201 anaerobes susceptible to clinafloxacin by broth microdilution was comparable to cefoxitin. Our data support the proposed disk diffusion interpretive criteria for aerobic bacteria with 5-microg clinafloxacin disks.
In vitro activities of the ketolide HMR 3647 against recent gram-positive clinical isolates and Haemophilus influenzae.
The ketolide HMR 3647 (previously RU 66647) was evaluated against 2, 563 recent clinical isolates of gram-positive pathogens and 200 Haemophilus influenzae isolates. HMR 3647 was active against macrolide-resistant streptococci, including pneumococci, but was not active against macrolide- or lincosamide-resistant staphylococci. Against H. influenzae, the potency of HMR 3647 was similar to that of azithromycin.
Quality control limits for dilution and disk diffusion susceptibility tests of trovafloxacin against eight quality control strains.
A 10-laboratory collaborative effort was designed to generate data to propose quality control limits for susceptibility tests of trovafloxacin. Broth microdilution, agar dilution, and disk diffusion tests were evaluated with eight different control strains. All tests were reproducible, and control limits are proposed.
Shaker-1 mutations reveal roles for myosin VIIA in both development and function of cochlear hair cells.
The mouse shaker-1 locus, Myo7a, encodes myosin VIIA and mutations in the orthologous gene in humans cause Usher syndrome type 1B or non-syndromic deafness. Myo7a is expressed very early in sensory hair cell development in the inner ear. We describe the effects of three mutations on cochlear hair cell development and function. In the Myo7a816SB and Myo7a6J mutants, stereocilia grow and form rows of graded heights as normal, but the bundles become progressively more disorganised. Most of these mutants show no gross electrophysiological responses, but some did show evidence of hair cell depolarisation despite the disorganisation of their bundles. In contrast, the original shaker-1 mutants, Myo7ash1, had normal early development of stereocilia bundles, but still showed abnormal cochlear responses. These findings suggest that myosin VIIA is required for normal stereocilia bundle organisation and has a role in the function of cochlear hair cells.
Urban particle-induced apoptosis and phenotype shifts in human alveolar macrophages.
Epidemiological studies report a small but positive association between short-term increases in airborne particulate matter and small increases in morbidity and mortality from respiratory and cardiovascular disease in urban areas. However, the lack of a mechanistic explanation to link particle exposure and human health effects makes it difficult to validate the human health effects. The present study tested the hypothesis that urban particles could cause apoptosis of human alveolar macrophages(AM) and a shift of their phenotypes to a higher immune active state, which would provide a mechanism to explain an inflammatory response. Freshly isolated human AM were incubated for 24 hr with urban particles (#1648 and #1649), Mount Saint Helen's ash (MSH), and residual oil fly ash (ROFA). Cell viability was assessed by trypan blue exclusion and apoptosis was demonstrated by morphology, cell death ELISA, and DNA ladder formation. Additionally, AM were characterized according to RFD1(+) (immune stimulatory macrophages) and RFD1(+)7(+) (suppressor macrophages) phenotypes by flow cytometry. ROFA particles caused AM necrosis at concentrations as low as 10 microg/ml, urban particles had no effect except at 200 microg/ml, and MSH had no effect at 200 microg/ml. ROFA (25 microg/ml) and particles #1648 or #1649 (100 microg/ml) caused apoptosis of AM by all three criteria, but 200 microg/ml MSH had no effect. Finally, 25 microg/ml ROFA and 100 microg/ml particles #1648 or #1649 up regulated the expression of the RFD1(+) AM phenotype, while only ROFA decreased the RFD1(+)7(+) phenotype. Consequently, ROFA and urban particles can induce apoptosis of human AM and increase the ratio of AM phenotypes toward a higher immune active state (i.e., increased RFD1(+):RFD1(+)7(+) ratio). Ifurban particles cause similar changes in vivo, this could result in lung inflammation and possible increased pulmonary and cardiovascular disease.