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Biomedical subjects

W Meyers

Publications and source records attributed to W Meyers.

At least 19 recordsLinked to original sources
PubMed1994

Single-strand conformation polymorphism analysis coupled with stratified DNA sequencing reveals reduced sequence variation in the su(s) and su(wa) regions of the Drosophila melanogaster X chromosome.

Single-strand conformation polymorphism (SSCP) analysis followed by DNA sequencing of stratified sub-samples was used to survey DNA polymorphism in the su(s) and su(wa) regions in a natural population of Drosophila melanogaster. su(s) and su(wa) are located near the telomere of the X chromosome, where the rate of crossing over per kilobase of DNA monotonically decreases toward the tip. SSCP was assessed in 12 noncoding segments amplified from the su(s) region (3213 bp) and in 8 noncoding segments amplified from the su(wa) region (1955 bp). Sets of segments were multiplexed in a single electrophoretic lane to increase the number of base pairs assayed per lane. Eight segments were monomorphic, and the other 12 segments exhibited two to four SSCP classes. Only four within-SSCP-class DNA sequence differences (a single nucleotide substitution) were observed among 24,360 bp compared within classes. The between-SSCP-class DNA sequence comparisons revealed 27 substitutions and 9 insertion/deletion polymorphisms. The average numbers of substitutional differences per site were 0.0010 and 0.0021 for su(s) and su(wa), respectively. These values are intermediate between those reported for the more distal y-ASC region (0.0004) and the more proximal Pgd locus (0.0024). This observation is consistent with the prediction of the hitchhiking-effect model-i.e., a monotonic increase in polymorphism as a function of crossing over per kilobase.

Animals↗
PubMed1994

Nature screen: an efficient method for screening natural populations of Drosophila for targeted P-element insertions.

The efficiency of molecular techniques is making it increasingly necessary to rely on reverse genetics to understand the function of genes. Tissue-specific libraries allow one to identify numerous genes that can be cloned, sequenced, and mapped and whose temporal and tissue-specific pattern of expression are well characterized but whose function remains unknown. In such cases, it is desirable to generate targeted mutations to examine the phenotype of loss-of-function lesions. Here we describe a method for identifying naturally occurring variants of Drosophila melanogaster with specific genes tagged by a nearby P element. Imprecise P-element excision can then be used to generate a series of small deletions in or near the gene. In the method described here, large numbers of wild-caught males were crossed to balancer females, and inserts were identified in pooled samples by the polymerase chain reaction with one primer from each target gene and one primer from the P-element terminal repeat. We present the calculations for the probability of successfully tagging a gene and show that it is greatly improved by simultaneously screening inserts into several genes. If a large natural population is available, a nature screen is faster and easier than inducing P-element transposition in the laboratory, but the resulting lines, being genetically heterogeneous, may require more subsequent work to isolate. Using this method to screen the genomes of approximately 10,400 males, we found P-element inserts in close proximity to 3 of 10 genes that were screened.

Animals↗
PubMed1994

Particle concentration fluorescence immunoassay chemosensitivity assay for human epithelial ovarian cancer.

We adapted particle concentration fluorescence immunoassay technology to develop a new chemosensitivity assay. Six human epithelial ovarian cancer cell lines were incubated with cisplatin for 24 hours. Cells were then labeled with a fluorophore for 30 minutes. Removal of supernatant, washing of tumor cells, and reading of epifluorescence was performed automatically. Percent cell lysis was calculated simultaneously by chromium release assay. The particle concentration fluorescence chemosensitivity assay detected cell lysis in all six cell lines. The chemosensitivity assay detected a larger percent lysis than the chromium release assay in each of the cell lines. The advantages of our chemosensitivity assay are plating efficacy, speed, efficiency, safety, and accuracy.

Cell Death↗
PubMed1990

Hepatic hemangiomas vs metastases: MR differentiation at 1.5 T.

We retrospectively studied the value of MR imaging at 1.5 T in distinguishing hepatic hemangiomas (n = 15) from metastases (n = 15) by using (1) lesion/liver signal-intensity ratios, (2) contrast/noise ratios, and (3) T2 relaxation time on long TR/TE spin-echo (SE) sequences. Lesion/liver margin sharpness, lesion shape, and overall lesion morphologic pattern were evaluated also. Univariate logistic regression analysis of the quantitative data showed that T2 was the only statistically significant (p less than .02) variable for distinguishing a hemangioma from a metastasis. A receiver-operator-characteristic plot of T2 produced an area of 0.80 (+/- 0.08). T2 values for these lesions still overlapped with those for metastases. Morphologically, hemangiomas were sharply marginated (80%), rounded or oval (93%), homogeneous, hyperintense lesions (73%), whereas metastases were poorly marginated (66%) and inhomogenous (67%) lesions. The marked, hyperintense appearance was present in 27% of metastases. Retrospective, multivariate logistic regression analysis of T2 and the presence of hyperintense morphology did not improve results based on T2 alone. Morphologic criteria are helpful in differentiation, as some metastases have a prolonged T2 and are not homogenous, hyperintense lesions. In cases where T2 or morphology are equivocal, other diagnostic tests may help confirm the MR findings. We currently use a T2 of greater than 88 msec and the presence of hyperintense morphology to diagnose hemangiomas. Despite both quantitative and qualitative analysis, data for these hemangiomas and metastases still overlap.

Adult↗
PubMed1989

An evaluation of volumes and concentrations of lidocaine in human inferior alveolar nerve block.

The purpose of this study was to evaluate, with the electric pulp tester, the anesthetic efficacy of 1.8 ml of 2% lidocaine with 1:100,000 epinephrine, 3.6 ml of 2% lidocaine with 1:200,000 epinephrine, and 1.8 ml of 4% lidocaine with 1:100,000 epinephrine in human inferior alveolar nerve block. Thirty subjects randomly received each of the solutions at three successive appointments. The first molar, canine, lateral incisor, and contralateral canine were tested with the pulp tester at various time intervals up to 55 min. Complete anesthesia was defined as an 80/80 reading with the pulp tester. No significant differences in anesthetic success or failure were found among the three solutions. Potential anesthetic problems (failure, noncontinuous anesthesia, slow onset, and short duration) occurred in 43 to 57% of the molars, in 43 to 60% of the canines, and in 57 to 80% of the lateral incisors. Complete anesthesia in the mandible is a meaningful clinical problem.

Adult↗
PubMed1989

An in vivo comparison of the step-back technique versus a step-back/ultrasonic technique in human mandibular molars.

This study compared the in vivo debridement efficacy of the step-back preparation versus a step-back/ultrasound preparation in the mesial root canals of vital human mandibular molars. Group 1 consisted of 15 teeth prepared with a step-back technique using intermittent irrigation with 5.25% sodium hypochlorite. Group 2 consisted of 23 teeth prepared with a step-back technique as in group 1 followed by 3 min of ultrasonic instrumentation (Cavi-Endo) using 5.25% sodium hypochlorite (30 ml per min). Group 3 consisted of 21 teeth which were uninstrumented and served as controls. Following extraction and histological preparation, the 1- and 3-mm levels of the canal and isthmus were evaluated for percentage of tissue removal using a compensating polar planimeter. At the 3-mm level, there were no statistical differences in canal or isthmus cleanliness between the step-back group and the step-back/ultrasound group. At the 1-mm apical level, statistical analysis indicated that the step-back/ultrasonic technique was superior to the step-back technique in canal (99.6% versus 88%) and isthmus (86% versus 10%) cleanliness.

Adult↗
PubMed1989

Limited improvement of tumour diagnosis by the simultaneous determination of carcinoembryonic antigen (CEA) and of a tumour-associated CEA-related antigen of Mr 128,000 in serum.

Two biotin-avidin based enzyme immunoassays were developed using three monoclonal anti-CEA antibodies with distinct epitope- and antigen-specificities. A broadly cross-reactive monoclonal anti-CEA antibody (T84.1) was immobilized on a solid support. Either monoclonal antibody T84.66 or CEA.11 was used as the second, biotin-labeled monoclonal antibody. Both antibodies do not cross-react with normal granulocytes or bile canaliculi. Monoclonal antibody CEA.11 binds to CEA and to an antigen with a relative molecular mass of 128,000 present in extracts from solid carcinomas. Monoclonal antibody T84.66 does not cross-react with the antigen of Mr 128,000. After adsorption of tumour extracts to a CEA-specific immunosorbent, residual activity was measurable by the CEA.11 assay, but not by the T84.66 assay. Serum samples (n = 726) from patients with malignant and non-malignant disease, as well as from healthy volunteers, were analysed by both immunoassays and by two commercial CEA immunoassays. In comparison with the T84.66 assay and the commercial assays, the CEA.11 assay did not significantly increase the sensitivity or specificity of tumour diagnosis.

Antibodies, Monoclonal↗
PubMed1988

[Significance of basal TSH and free T3 as compared with an extended in vitro diagnosis in the understanding of functional disorders of the thyroid].

Data of 411 untreated patients undergoing thyroid investigations were stored in a data base system. Three combinations of thyroidal hormone parameters were compared with respect to their clinical value. In patients with concordant basal TSH (bTSH) and free T3 (fT3)-values (e.g. bTSH normal and fT3 normal, bTSH decreased and fT3 increased) it could be demonstrated that the predictive value of the combined evaluation of basal TSH (supersensitive) and free T3 alone (97% in normal thyroid function, 98% in thyrotoxicosis, and 97% in hypothyroidism) was sufficient. Additional determinations of T4 parameters did not increase predictive value (e.g. TT4: 95% in thyrotoxicosis). Thus, thyroid disorders may currently be diagnosed by the combined evaluation of basal TSH and free T3, saving costs without loss of diagnostic efficacy.

Clinical Laboratory Techniques↗
PubMed1981

Effect of apolipoproteins on the induction of hepatic steatosis in rats.

The incorporation of apolipoprotein E isolated from human very low density lipoproteins on a triglyceride emulsion produced a substantial increment in hepatic triglyceride after 1 h of in vitro perfusion through the isolated liver of a fasted rat. Both gross and microscopic morphology confirmed a substantial steatosis. Perfusions with triglyceride emulsions which contained no apoipoproteins resulted in a modest increment in hepatic triglyceride although considerably less than emulsions with the E protein, and no morphologic features of steatosis. The steatosis induced in the in vitro perfused fasted livers by the emulsions with E protein could be prevented when CIII-1 apoprotein was also incorporated on the emulsion. A fed rat liver perfused with the E-enriched emulsion accumulated significantly less triglyceride than the fasted preparation. These data suggest that the apoprotein patterns of the plasma triglyceride-rich lipoproteins are of considerable importance for the partition of triglyceride between liver and plasma.

Animals↗
PubMed1980

Effect of apoproteins on hepatic uptake of triglyceride emulsions in the rat.

The addition of apoprotein E isolated from human very low density lipoproteins to both rat lymph chylomicrons and a triglyceride emulsion significantly increased the hepatic uptake of these particles in a nonrecycling isolated rat liver perfusion system. The cleared triglyceride was removed without apparent hydrolysis by the hepatocyte. When lymph chylomicrons were loaded with both Apo E and Apo C proteins by exposure to rat plasma, no increment in hepatic clearance was observed. Sequential evalutions of the influence of the C apoproteins on the hepatic clearance of both emulsions and chylomicrons revealed that the CIII (CIII-1) protein had a pronounced inhibitory effect on hepatic removal. The inhibition was observed for both Apo E-enriched chylomicrons and those containing little of this apoprotein.

Animals↗