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Biomedical subjects

E L Davis

Publications and source records attributed to E L Davis.

At least 19 recordsLinked to original sources
PubMed2001

Molecular characterisation and expression of two venom allergen-like protein genes in Heterodera glycines.

Secretory proteins encoded by genes expressed in the oesophageal gland cells of plant-parasitic nematodes have key roles in nematode parasitism of plants. Two venom allergen-like protein cDNAs (designated hg-vap-1 and hg-vap-2)were isolated from Heterodera glycines gland cell cDNA libraries. Both cDNAs hybridised to genomic DNA of H. glycines in Southern blots. The hg-vap-1 cDNA contained an open reading frame encoding 215 amino acids with the first 25 amino acids being a putative secretion signal. The hg-vap-2 cDNA contained an open reading frame encoding 212 amino acids with the first 19 amino acids being a putative secretion signal. Genes of hg-vap-1 and hg-vap-2 contained four introns, which ranged in size from 44 to 574 bp, and five exons ranging in size from 43 to 279 bp. In situ hybridisation analyses showed that mRNAs of both vap genes accumulated specifically in the subventral gland cells of H. glycines during parasitism. The gland cell-specific expression and presence of predicted secretion signal peptides in both VAPs suggest that these proteins are secreted from the nematode and may play a role in the infection of host plants by this parasite.

Allergens↗
PubMed2001

Identification of putative parasitism genes expressed in the esophageal gland cells of the soybean cyst nematode Heterodera glycines.

Cloning parasitism genes encoding secretory proteins expressed in the esophageal gland cells is the key to understanding the molecular basis of nematode parasitism of plants. Suppression subtractive hybridization (SSH) with the microaspirated contents from Heterodera glycines esophageal gland cells and intestinal region was used to isolate genes expressed preferentially in the gland cells of parasitic stages. Twenty-three unique cDNA sequences from a SSH cDNA library were identified and hybridized to the genomic DNA of H. glycines in Southern blots. Full-length cDNAs of 21 clones were obtained by screening a gland-cell long-distance polymerase chain reaction cDNA library. Deduced proteins of 10 clones were preceded by a signal peptide for secretion, and PSORT II computer analysis predicted eight proteins as extracellular, one as nuclear, and one as plasmalemma localized. In situ hybridization showed that four of the predicted extracellular clones were expressed specifically in the dorsal gland cell, one in the subventral gland cells, and three in the intestine in H. glycines. The predicted nuclear clone and the plasmalemma-localized clone were expressed in the subventral gland cells and the dorsal gland cell, respectively. SSH is an efficient method for cloning putative parasitism genes encoding esophageal gland cell secretory proteins that may have a role in H. glycines parasitism of soybean.

Animals↗
PubMed2001

Signal peptide-selection of cDNA cloned directly from the esophageal gland cells of the soybean cyst nematode Heterodera glycines.

Secretions from the esophageal gland cells of plant-parasitic nematodes play critical roles in the nematode-parasitic cycle. A novel method to isolate cDNA encoding putative nematode secretory proteins was developed that utilizes mRNA for reverse transcription-polymerase chain reaction derived from microaspiration of the esophageal gland cell contents of parasitic stages of the soybean cyst nematode Heterodera glycines. The resulting H. glycines gland cell cDNA was cloned into the pRK18 vector, and plasmid DNA was transformed into a mutated yeast host for specific selection of cDNA inserts that encode proteins with functional signal peptides. Of the 223 cDNA clones recovered from selection in yeast, 97% of the clones encoded a predicted signal peptide. Fourteen unique cDNA clones hybridized to genomic DNA of H. glycines on Southern blots and, among them, nine cDNA clones encoded putative extracellular proteins, as predicted by PSORT II computer analysis. Four cDNA clones hybridized to transcripts within the dorsal esophageal gland cell of parasitic stages of H. glycines, and in situ hybridization within H. glycines was not detected for eight cDNA clones. The protocol provides a direct means to isolate potential plant-parasitic nematode esophageal gland secretory protein genes.

Animals↗
PubMed2001

Endo-beta-1,4-glucanase expression in compatible plant-nematode interactions.

Cyst nematodes and root-knot nematodes elaborately transform cells within the vascular cylinders of plant roots into enlarged, multinucleate, and metabolically active feeding cells. The giant cells of root-knot nematodes are formed by repeated karyokinesis uncoupled from cytokinesis, whereas the syncytia formed by cyst nematodes arise from coordinated cell wall dissolution and the coalescing of cell cytoplasm of adjacent cells. Both giant cells and syncytia undergo extensive cell wall architectural modifications, including thickening and the formation of numerous ingrowths that increase the plasmalemma surface area for solute uptake. The origin of enzymes involved in these cell wall modifications has been the subject of debate for several decades. Immunolocalization of endo-beta-1,4-glucanases (EGases) secreted from cyst nematodes was observed in root cortical tissue during the intracellular migration of the nematodes, but secretion of cyst nematode EGases into developing syncytia was not detected. We have identified five EGase genes from tobacco that are upregulated within plant roots upon infection by both root-knot and cyst nematodes. In situ localization of tobacco EGase transcripts demonstrated that their expression was specifically and developmentally upregulated within giant cells, syncytia, root tips, and lateral root primordia. These data confirm that cell wall modifications within plant-parasitic-nematode feeding cells arise from cell wall-modifying enzymes of plant, rather than nematode, origin.

Amino Acid Sequence↗
PubMed1999

Comparison of accuracy between compression- and injection-molded complete dentures.

STATEMENT OF PROBLEM: A clinically significant incisal pin opening may occur after processing complete dentures if a compression molding technique is used. To recover the proper vertical dimension of occlusion, a time-consuming occlusal adjustment is necessary that often destroys the anatomy of the artificial teeth. A new injection molding process claims to produce dentures that require few, if any, occlusal adjustments in the laboratory after processing. PURPOSE: This laboratory study compared incisal pin opening, dimensional accuracy, and laboratory working time for dentures fabricated by this new injection system with dentures constructed by the conventional compression molding technique. MATERIAL AND METHODS: Two groups of 6 maxillary and 6 mandibular dentures were evaluated as follows: group 1 (control), Lucitone 199, compression molded with a long cure cycle; and group 2, Lucitone 199, injection molded with a long cure. Incisal pin opening was measured with a micrometer immediately after deflasking. A computerized coordinate measuring machine was used to measure dimensional accuracy of 3-dimensional variations in selected positions of artificial teeth in 4 stages of denture fabrication. Analysis of variance (ANOVA) and t tests were performed to compare the groups. RESULTS: A significant difference was found in pin opening between groups (t test). Horizontal dimensional changes evaluated with repeated measures ANOVA revealed no significant differences between groups. However, analysis of vertical dimensional changes disclosed significant differences between the groups. There was no appreciable difference in laboratory working time for flasking and molding denture bases between the injection and compression molding techniques when polymethyl methacrylate resin was used. CONCLUSION: The injection molding method produced a significantly smaller incisal pin opening over the standard compression molding technique. The injection molding technique, using polymethyl methacrylate, was a more accurate method for processing dentures. There were no appreciable differences in laboratory working time between the injection and compression molding techniques.

Analysis of Variance↗
PubMed1999

Developmental expression of secretory beta-1,4-endoglucanases in the subventral esophageal glands of Heterodera glycines.

Two beta-1,4-endoglucanases (EGases), Hg-eng-1 and Hg-eng-2, were recently cloned from the soybean cyst nematode, Heterodera glycines, and their expression was shown in the subventral esophageal glands of hatched second-stage juveniles (J2). We examined the expression of these EGases in the subventral glands of all post-embryonic life stages of H. glycines by in situ hybridization and immunolocalization. The first detectable accumulation of EGase mRNAs occurred in the subventral glands of unhatched J2. EGase transcripts remained detectable in J2 after hatching and during subsequent root invasion. However, in late parasitic J2 and third-stage juveniles (J3), the percentage of individuals that showed EGase transcripts decreased. In female fourth-stage juveniles and adult females, EGase transcripts were no longer detected in the subventral glands. EGase hybridization signal reappeared in unhatched males coiled within the J3 cuticle, and transcripts were also present in the subventral glands of migratory adult males. Immunofluorescence labeling showed that EGase translation products are most abundantly present in the subventral glands of preparasitic J2, migratory parasitic J2, and adult males. The presence of EGases predominantly in the migratory stages suggests that the enzymes are used by the nematodes to soften the walls of root cells during penetration and intracellular migration.

Animals↗
PubMed1998

Endogenous cellulases in animals: isolation of beta-1, 4-endoglucanase genes from two species of plant-parasitic cyst nematodes.

beta-1,4-Endoglucanases (EGases, EC 3.2.1.4) degrade polysaccharides possessing beta-1,4-glucan backbones such as cellulose and xyloglucan and have been found among extremely variegated taxonomic groups. Although many animal species depend on cellulose as their main energy source, most omnivores and herbivores are unable to produce EGases endogenously. So far, all previously identified EGase genes involved in the digestive system of animals originate from symbiotic microorganisms. Here we report on the synthesis of EGases in the esophageal glands of the cyst nematodes Globodera rostochiensis and Heterodera glycines. From each of the nematode species, two cDNAs were characterized and hydrophobic cluster analysis revealed that the four catalytic domains belong to family 5 of the glycosyl hydrolases (EC 3.2.1, 3.2.2, and 3.2.3). These domains show 37-44% overall amino acid identity with EGases from the bacteria Erwinia chrysanthemi, Clostridium acetobutylicum, and Bacillus subtilis. One EGase with a bacterial type of cellulose-binding domain was identified for each nematode species. The leucine-rich hydrophobic core of the signal peptide and the presence of a polyadenylated 3' end precluded the EGases from being of bacterial origin. Cyst nematodes are obligatory plant parasites and the identified EGases presumably facilitate the intracellular migration through plant roots by partial cell wall degradation.

Amino Acid Sequence↗
PubMed1998

Clinical wear study of three commercially available artificial tooth materials: thirty-six month results.

STATEMENT OF PROBLEM: Excessive wear of artificial resin teeth has been a concern to both the patient and the dentist because of unfavorable associated sequelae. The search for a more wear resistant resin tooth material resulted in the development of modified resin teeth that displayed acceptable wear resistance. PURPOSE: This study compared clinical wear of a new modified resin tooth material with two other commercially available modified resin materials over a period of 36 months. Differences in wear by gender, cuspal anatomy, arch, individual tooth type, and chewing side preference were also evaluated. MATERIAL AND METHODS: A total of 67 patients were randomized into one of three treatment groups in this double-blind study; group 1, Ivoclar-Vivodent and Orthotyp; group 2, Dentsply-Trublend SLM; and group 3, Dentsply-Bioblend IPN. Tooth wear was determined by measuring vertical heights of contacting points at baseline and 36 months with a computerized coordinate measuring machine and computer-controlled positioning stages. Measurements were completed at 36 months for 55 patients who remained in the study. RESULTS: Repeated measures analysis of variance revealed no significant difference in total wear by gender or tooth material at 36 months. There was also no significant difference by chewing side preference or cuspal anatomy. However, there was a significant difference in individual tooth wear (canine, premolar, molar) and by arch. CONCLUSION: New modified resin teeth have displayed clinically acceptable wear resistance for most patients.

Acrylic Resins↗
PubMed1997

Amplification of Guthrie card DNA: effect of guanidine thiocyanate on binding of natural whole blood PCR inhibitors.

Amplification of DNA from whole blood collected on Guthrie card filter paper presents considerable technical obstacles due to the presence of natural PCR inhibitors (protein, heavy metals, heme, and heme degradation products) and low copy number of genomic material. For this purpose we evaluated guanidine thiocyanate-impregnated filter paper (GT-903), a DNA collection device designed specifically to bind PCR inhibitors and preserve DNA in an aqueous extractable form. Compared to standard 903, which retains DNA and elutes inhibitors during aqueous extraction, we found GT-903 retained 90% of protein, hemoglobin, and iron. SDS-PAGE analysis indicated that the majority of the protein released from standard 903 corresponded to albumin (70-) and globin (15-kDa); negligible levels of these proteins were eluted from GT-903. To evaluate PCR efficiency, we amplified the 491 bp region encoding the cystic fibrosis delta F508 mutation. Using comparable template, we found GT-903 amplification more efficient than standard 903 following qualitative (TBE-PAGE) and quantitative (anti-dsDNA EIA) determination. We conclude that GT-903 provides a good DNA collection device and addresses the complications associated with natural PCR inhibitors.

Binding Sites↗
PubMed1997

An assessment of the intellectual development of dental students.

William Perry proposed that students' underlying reasoning structures can be assessed by eliciting their perceptions of their educational experiences. His research demonstrated that cognitive development occurs in stages and that not all students at the same educational level display the same level of intellectual development. He suggested that curricular interventions are necessary to enable students at lower stages to develop the cognitive structures that facilitate such higher level tasks as making critical judgments and evaluating alternatives. The present study determined the level of intellectual development of first-year, fourth-year, and postdoctoral dental students using the Perry model. Scores on the Measure of Epistemological Reflection (MER), used to indicate Perry level, suggest that these students, on average, are in the early multiplicity stage of development. Comparison of mean scores indicated significantly different Perry levels only between first- and fourth-year dental students.

Adult↗
PubMed1996

Secretory granule proteins from the subventral esophageal glands of the potato cyst nematode identified by monoclonal antibodies to a protein fraction from second-stage juveniles.

Sodium dodecyl sulfate-extracted proteins from second-stage juveniles (J2) of the potato cyst nematode Globodera rostochiensis were fractionated by preparative continuous flow electrophoresis, and monoclonal antibodies (MAbs) were raised against the 38- to 40.5-kDa protein fraction. Screening of the hybridoma culture fluids by immunofluorescence microscopy of J2 resulted in the identification of 12 MAbs that bound specifically to the subventral esophageal glands. On Western blots of J2 these MAbs identified four protein bands with apparent molecular masses of 30, 31, 39, and 49 kDa. Immunoelectron microscopy with one of these MAbs showed an intense labeling of the electron dense core of the secretory granules in the subventral gland cells of J2. It is concluded that one or more of these proteins are localized within these secretory granules. Immunofluorescence microscopy of J2 from other plant parasitic nematode species showed that most of these MAbs also bind to the subventral glands of G. pallida and G. tabacum but not of Heterodera schachtii, H. glycines, Meloidogyne incognita, or M. hapla.

Animals↗
PubMed1996

Survey of ethical issues in dental research.

The American Association for Dental Research (AADR) surveyed its leaders to determine their perceptions of the prevalence of problematic research practices and the possible roles AADR should play in promoting scientific integrity. Seventy-six of the 98 program chairs and Association officers (1990-1995) surveyed responded. In general, these respondents did not think that serious misconduct or sloppy science occurred more often in AADR than in other scientific disciplines. Overall, respondents rated practices that undermine the trustworthiness of science (falsifying or fabrication of research data, retaliation, failure to present negative results, failure to disclose involvement with commercial enterprises, failure to maintain research records, etc.) as more serious, but less prevalent, than practices considered disrespectful of the work of others (gift authorship, citing sources without reading them, dividing a project into many small units, etc.). All respondents said that they had observed each of the less serious problematic practices one or more times, whereas 10% reported having observed retaliation, 30% reported having observed falsification, and 54% reported having observed plagiarism one or more times. AADR leaders had observed many more instances of misconduct and other problematic research practices than had faculty surveyed by Swazey et al. (1993), supporting conclusions by Greenberg and Goldberg (1994) that status and years of experience are associated with more frequent observations of misconduct. With respect to the possible roles the AADR might play in promoting research integrity, 88% thought that AADR should develop ethics cases and materials for educational use, 78% thought that AADR should create a process for addressing allegations of misconduct, 72% thought that the Association should develop an ethics committee or consultation service, 55% thought it should create a yearly ethics symposium, and 45% thought that the AADR should develop a more specific code of ethics to complement the general code recently developed by the IADR.

Administrative Personnel↗
PubMed1995

Twelve-month results of a clinical wear study of three artificial tooth materials.

This study compared in vivo wear of a new artificial tooth material with that of existing artificial tooth materials. Artificial tooth wear was determined by measuring height changes of selected points on contacting tooth surfaces in patients with complete dentures during a 12-month period. These results are part of an ongoing 3-year clinical study. A total of 67 patients were randomized to one of three treatment groups in this double-blind study. Group 1 received dentures with existing artificial tooth materials. Group 2 received dentures that contained teeth with the new experimental material. Group 3 received dentures with Bioform IPN resin teeth (Dentsply International Inc., York, Pa). A computerized coordinate measuring machine and computer-controlled X-Y positioning stages were used for this study. Tooth wear was determined by measuring vertical heights of contacting points from baseline points at each of two time intervals. The calculation of wear was made by comparing the differences in height at the beginning of the experiment with those measured at each time interval. A repeated measures analysis of variance (ANOVA) was used to test the difference in mean wear among the three groups from baseline to 6 months and from 6 to 12 months. Group differences in total wear at 12 months were also tested. The ANOVA results revealed no statistically significant differences in the wear among the three types of denture teeth at the 6- or 12-month time intervals or at 12 months (p > 0.05). The average total wear value at 12 months was 90 microns. Group 1 averaged 102 microns of wear, group 2 averaged 88 microns of wear, and group 3 averaged 76 microns of wear.

Acrylic Resins↗
PubMed1995

Effect of restorative materials on cuspal flexure.

The purposes of this study were (1) to establish a methodology for determining surface strains in two locations of the same tooth under intact, prepared, and restored conditions and (2) to compare the effects on stiffness of different restorative materials in a tooth subjected to cuspal loading. Two linear strain gauges were mounted on each of 30 extracted maxillary premolar teeth. Teeth were mounted in poly(methyl methacrylate) resin and randomly assigned to one of three study groups according to the restorative material and application technique to be used. Statistical analysis indicated a statistically significant interaction between restorative material and tooth condition at both proximal and buccal sites and a statistically significant difference in stiffness between teeth restored with Tenure/Marathon V and those restored with either amalgam or Scotchbond 2/P-50 at the proximal site. Results suggest that the methods employed provide a useful, nondestructive means of testing the same tooth under various conditions.

Analysis of Variance↗
PubMed1993

Adhesion to dentin.

Significant advances have been made in the development of systems that adhere to dentin, and restorative dentistry is fast approaching the development of a group of materials that will provide a strong and durable bond to dentin. Newer dentin-bonding systems, requiring alteration or complete removal of the smear layer, in general produce stronger bonds, and appear to provide a more effective marginal seal, than smear layer-dependent bonding systems. Some of these newer bonding agents have developed bond strengths to dentin comparable to those achieved with acid-etched enamel surfaces. However, for situations in which the retentive form of the cavity preparation is particularly critical to the success of the restoration, traditional retentive features should be used in the cavity design.

Dental Bonding↗
PubMed1993

Dentin bonding system shelf life and bond strength.

The purpose of this study was to assess the shelf life of dentin bonding systems by means of bond strength testing. The systems evaluated were Mirage-Bond, All-Bond and Tenure. Specimens were tested immediately, and 1, 2, 3, 4, 5 and 12 months after opening the kits. Flat dentin surfaces were created on 210 extracted human molars that had been stored in saline. Ten specimens were prepared for each dentin bonding system at each shelf time. Each material was prepared and placed following the manufacturer's instructions. Prisma MicroFine resin composite was then placed. Shear bond strength testing was conducted using a universal testing machine. A two-way ANOVA indicated a significant interaction between bonding system and storage time (F = 2.28, P = 0.01). Multiple comparison tests indicated statistically significant bond strength differences by storage time for All-Bond and Mirage-Bond. In addition, a comparison of bonding systems at each storage time revealed significant differences at three of the seven times. These results suggest that shelf life for two of the three dentin bonding systems may be significantly shorter than currently presumed.

Analysis of Variance↗
PubMed1993

Shear strength and microleakage of light-cured glass ionomers.

Bond to dentin and marginal integrity of three light activated glass ionomer cements were evaluated, and compared to a traditional chemical-cured glass ionomer cement. Results indicated no significant difference in shear bond strength among the glass ionomer cements tested. However, there was a significant difference among glass ionomer cements in bond strength variability, with coefficients of variation ranging from 55 to 102%. A discrepancy between manufacturers' instructions and optimum curing times is one possible explanation for these results. There were also no significant differences in microleakage among glass ionomer cements. Most samples exhibited minimal or no microleakage.

Analysis of Variance↗