Biomedical subjects

C Stephens

Publications and source records attributed to C Stephens.

At least 19 recordsLinked to original sources

PubMed2025

Chromosome scale genomes of two invasive Adelges species enable virtual screening for selective adelgicides.

Two invasive hemipteran adelgids are associated with widespread damage to several North American conifer species. Adelges tsugae, hemlock woolly adelgid, was introduced from Japan and reproduces parthenogenetically in North America, where it has rapidly decimated Tsuga canadensis and Tsuga caroliniana (the eastern and Carolina hemlocks, respectively). Adelges abietis, eastern spruce gall adelgid, introduced from Europe, forms distinctive pineapple-shaped galls on several native spruce species. While not considered a major forest pest, it weakens trees and increases susceptibility to additional stressors. Broad-spectrum insecticides that are often used to control adelgid populations can have off-target impacts on beneficial insects. Whole genome sequencing was performed on both species to aid in development of targeted solutions that may minimize ecological impact. Adelges abietis was sequenced using Illumina Linked-Read technology from 30 pooled individuals, with Hi-C scaffolding performed using data from a single individual collected from the same host plant. Adelges tsugae used Oxford Nanopore long-read sequencing from pooled nymphs. The assembled A. tsugae and A. abietis genomes, pooled from several parthenogenetic females, are 220.75 Mbp and 253.16 Mbp, respectively. Each consists of eight autosomal chromosomes, as well as two sex chromosomes (X1/X2), supporting the XX-XO sex determination system. The genomes are over 96% complete based on BUSCO assessment. Genome annotation identified 11,424 and 12,060 protein-coding genes in A. tsugae and A. abietis, respectively. Comparative analysis of proteins across 29 hemipteran species and 14 arthropod outgroups identified 31,666 putative gene families. Gene family evolution analysis with CAFE revealed lineage-specific expansions in immune-related aminopeptidases (ERAP1) and juvenile hormone binding proteins (JHBP), contractions in juvenile hormone acid methyltransferases (JHAMT), and conservation of nicotinic acetylcholine receptors (nAChR). These genes were explored as candidate families towards a long-term objective of developing adelgid-selective insecticides. Structural comparisons of proteins across seven focal species (Adelges tsugae, Adelges abietis, Adelges cooleyi, Rhopalosiphum maidis, Apis mellifera, Danaus plexippus, and Drosophila melanogaster) revealed high conservation of nAChR and ERAP1, while JHAMT exhibited species-specific structural divergence. The potential of JHAMT as a lineage-specific target for pest control was explored through virtual drug and pesticide screening.

adelgids↗

PubMed1999

Bacterial cells: The migrating kinase and the master regulator.

It is becoming clear that, as in eukaryotes, proteins in bacterial cells are targeted to specific cellular locations. The most recently discovered example is a remarkable histidine kinase that oscillates between polar and global distributions while temporally regulating transcription and DNA replication in Caulobacter.

Bacterial Proteins↗

PubMed1999

The characteristics of traumatic events experienced by nurses on the accident and emergency ward.

Nurses who work in high-risk areas, such as emergency wards, are susceptible to traumatic stress. The present study is an exploratory one, which attempts to describe and interpret some event characteristics of traumatic incidents identified by nurses. Nine nurses from the Accident and Emergency wards of two New Zealand hospitals were interviewed using the repertory grid technique. Qualitative analysis was used to compare event characteristics across participants and four underlying themes were identified: personal issues, contextual issues, control issues, or organisational issues. Comparison of these results with previous work with high stress occupations suggests that although event characteristics from all groups can be broadly grouped under four themes, there are some distinct differences in the traumatic impact of some event characteristics for nurses. The results have implications in the development of measures of traumatic stress for nurses and have immediate implications for organisational practice.

Burnout, Professional↗

PubMed1999

Safety, pharmacokinetics, and tissue distribution of liposomal P-ethoxy antisense oligonucleotides targeted to Bcl-2.

Antisense oligonucleotides (oligos) have the ability to selectively block disease-causing genes, thereby inhibiting production of disease-associated proteins. However, their effectiveness has been limited by their low intracellular delivery. We had previously demonstrated that liposomes could increase the intracellular uptake of P-ethoxy oligos, hydrophobic analogs of phosphodiesters, and that liposomal Bcl-2 P-ethoxy antisense oligos (L-Bcl-2) could selectively inhibit Bcl-2 protein production, thereby inducing growth inhibition in Follicular Lymphoma cell lines. To understand the in vivo behavior of L-Bcl-2, we conducted a series of studies to evaluate the safety, pharmacokinetics, and tissue distribution of i.v. injections of L-Bcl-2 in normal rodents. Daily administration of 20 mg of L-Bcl-2/kg of body weight in 5 consecutive days had no adverse effects on renal or hepatic functions, nor on hematological parameters. Histopathology also did not reveal any significant changes in the morphology of the organs studied. In rats, the area under the curve of L-Bcl-2 reflects a two-compartment model of distribution with a biphasic plasma clearance. The T(1/2alpha) and T(1/2beta) were approximately 8 min and 4.2 h, respectively, and the V(d) was 79 ml, indicating a broad body distribution. The highest concentrations of L-Bcl-2 were found in spleen > liver > kidneys. These studies showed that in the schedules studied no significant toxicity associated with L-Bcl-2 was observed over 6 weeks, and that L-Bcl-2 could be widely distributed in the body.

Animals↗

PubMed1998

A cell cycle-regulated adenine DNA methyltransferase from Caulobacter crescentus processively methylates GANTC sites on hemimethylated DNA.

The kinetic properties of an adenine DNA methyltransferase involved in cell cycle regulation of Caulobacter crescentus have been elucidated by using defined unmethylated or hemimethylated DNA (DNAHM) substrates. Catalytic efficiency is significantly enhanced with a DNAHM substrate. Biphasic kinetic behavior during methyl incorporation is observed when unmethylated or DNAHM substrates are used, indicating that a step after chemistry limits enzyme turnover and is most likely the release of enzyme from methylated DNA product. The enzyme is thermally inactivated at 30 degrees C within 20 min; this process is substantially decreased in the presence of saturating concentrations of DNAHM, suggesting that the enzyme preferentially binds DNA before S-adenosylmethionine. The activity of the enzyme shows an unusual sensitivity to salt levels, apparently dissociating more rapidly from methylated DNA product as the salt level is decreased. The enzyme acts processively during methylation of specific DNA sequences, indicating a preferred order of product release in which S-adenosylhomocysteine is released from enzyme before fully methylated DNA. The kinetic behavior and activity of the enzyme are consistent with the temporal constraints during the cell cycle-regulated methylation of newly replicated chromosomal DNA.

Caulobacter crescentus↗

PubMed1998

Bacterial sporulation: a question of commitment?

Starved Bacillus subtilis cells monitor environmental conditions and intracellular events before committing to sporulation. The precise identity of the sporulation-inducing signals is an open question, but recent results suggest strategies by which Bacillus integrates diverse signals in the decision-making process.

Bacillus subtilis↗

PubMed1998

The validation of an orthodontic expert system rule-base for fixed appliance treatment planning.

A peer review clinical trial was undertaken to assess the appropriateness of the advice produced by an expert system designed to plan orthodontic treatment in which the pre-adjusted bracket appliance was to be used. The results showed that the expert system's treatment plans were as reliable as those produced by a group of orthodontists. Two members of the panel actually ranked the expert system's plans more highly than their own.

Adolescent↗

PubMed1998

Development of a computer-assisted learning software package on dental traumatology.

The development of computer-assisted learning software packages is a relatively new field of computer application. The progress made in personal computer technology toward more user-friendly operating systems has stimulated the academic community to develop computer-assisted learning for pre- and postgraduate students. The ability of computers to combine audio and visual data in an interactive form provides a powerful educational tool. The purpose of this study was to develop and evaluate a computer-assisted learning package on dental traumatology. This program contains background information on the diagnosis, classification, and management of dental injuries in both the permanent and the deciduous dentitions. It is structured into chapters according to the nature of the injury and whether injury has occurred in the primary or permanent dentition. At the end of each chapter there is a self-assessment questionnaire as well as references to relevant literature. Extensive use of pictures and video provides a comprehensive overview of the subject.

Computer-Assisted Instruction↗

PubMed1997

Bacterial protein secretion--a target for new antibiotics?

The heavy use of antibiotics over recent decades has resulted in widespread resistance of bacteria to many drugs. Overcoming resistance requires new approaches to antibiotic development, including the exploitation of new targets in the bacterial cell. Protein secretion is essential for bacterial cell growth and virulence, so it could be a suitable target for new therapeutic agents.

Anti-Bacterial Agents↗

PubMed1997

Identification of the fliI and fliJ components of the Caulobacter flagellar type III protein secretion system.

Caulobacter crescentus is motile by virtue of a polar flagellum assembled during the predivisional stage of the cell cycle. Three mutant strains in which flagellar assembly was blocked at an early stage were isolated. The mutations in these strains mapped to an operon of two genes, fliI and fliJ, both of which are necessary for motility. fliI encodes a 50-kDa polypeptide whose sequence is closely related to that of the Salmonella typhimurium FliI protein, an ATPase thought to energize the export of flagellar subunits across the cytoplasmic membrane through a type III protein secretion system. fliJ encodes a 16-kDa hydrophilic protein of unknown function. Epistasis experiments demonstrated that the fliIJ operon is located in class II of the C. crescentus flagellar regulatory hierarchy, suggesting that the gene products act at an early stage in flagellar assembly. The expression of fliIJ is induced midway through the cell cycle, coincident with other class II operons, but the FliI protein remains present throughout the cell cycle. Subcellular fractionation showed that FliI is present both in the cytoplasm and in association with the membrane. Mutational analysis of FliI showed that two highly conserved amino acid residues in a bipartite ATP binding motif are necessary for flagellar assembly.

Amino Acid Sequence↗

PubMed1997

The CcrM DNA methyltransferase is widespread in the alpha subdivision of proteobacteria, and its essential functions are conserved in Rhizobium meliloti and Caulobacter crescentus.

The Caulobacter crescentus DNA methyltransferase CcrM (M.CcrMI) methylates the adenine residue in the sequence GANTC. The CcrM DNA methyltransferase is essential for viability, but it does not appear to be part of a DNA restriction-modification system. CcrM homologs are widespread in the alpha subdivision of gram-negative bacteria. We have amplified and sequenced a 258-bp region of the cerM gene from several of these bacteria, including Rhizobium meliloti, Brucella abortus, Agrobacterium tumefaciens, and Rhodobacter capsulatus. Alignment of the deduced amino acid sequences revealed that these proteins constitute a highly conserved DNA methyltransferase family. Isolation of the full-length ccrM genes from the aquatic bacterium C. crescentus, the soil bacterium R. meliloti, and the intracellular pathogen B. abortus showed that this sequence conservation extends over the entire protein. In at least two alpha subdivision bacteria, R. meliloti and C. crescentus, CcrM-mediated methylation has important cellular functions. In both organisms, CcrM is essential for viability. Overexpression of CcrM in either bacterium results in defects in cell division and cell morphology and in the initiation of DNA replication. Finally, the C. crescentus and R. meliloti ccrM genes are functionally interchangeable, as the complemented strains are viable and the chromosomes are methylated. Thus, in both R. meliloti and C. crescentus, CcrM methylation is an integral component of the cell cycle. We speculate that CcrM-mediated DNA methylation is likely to have similar roles among alpha subdivision bacteria.

Amino Acid Sequence↗

PubMed1996

Delivering the payload. Bacterial pathogenesis.

A specialized protein secretion pathway is used by some Gram-negative bacterial pathogens for delivery of virulence factors directly into mammalian host cells. This pathway is parallel to, and probably evolved from, a system used for construction of the bacterial flagellum.

Bacterial Proteins↗

PubMed1996

Caulobacter Lon protease has a critical role in cell-cycle control of DNA methylation.

CcrM, an adenine DNA methyltransferase, is essential for viability in Caulobacter crescentus. The CcrM protein is present only in the predivisional stage of the cell cycle, resulting in cell-cycle-dependent variation of the DNA methylation state of the chromosome. The availability of CcrM is controlled in two ways: (1) the ccrM gene is transcribed only in the predivisional. cell, and (2) the CcrM protein is rapidly degraded prior to cell division. We demonstrate here that CcrM is an important target of the Lon protease pathway in C. crescentus. In a lon null mutant, ccrM transcription is still temporally regulated, but the CcrM protein is present throughout the cell cycle because of a dramatic increase in its stability that results in a fully methylated chromosome throughout the cell cycle. Because the Lon protease is present throughout the cell cycle, it is likely that the level of CcrM in the cell is controlled by a dynamic balance between temporally varied transcription and constitutive degradation. We have shown previously that restriction of CcrM to the C. crescentus predivisional cell is essential for normal morphogenesis and progression through the cell cycle. Comparison of the lon null mutant strain with a strain whose DNA remains fully methylated as a result of constitutive expression of ccrM suggests that the effect of Lon on DNA methylation contributes to several developmental defects observed in the lon mutant. These defects include a frequent failure to complete cell division and loss of precise cell-cycle control of initiation of DNA replication. Other developmental abnormalities exhibited by the lon null mutant, such as the formation of abnormally long stalks, appear to be unrelated to altered chromosome methylation state. The Lon protease thus exhibits pleiotropic effects in C. crescentus growth and development.

ATP-Dependent Proteases↗

PubMed1996

Promoting use of a preferred histamine H2-receptor antagonist in managed care organizations.

A program to promote generic cimetidine as the preferred histamine H2-receptor antagonist (HRA) in the managed care organizations (MCOs) served by a pharmacy benefit management company is described. A pharmacy benefit management company conducted a literature review to substantiate the therapeutic equivalence of the HRAs and to set conservative criteria for identifying candidates for conversion to oral cimetidine therapy. During the third quarter of 1994, the prescriber for each patient identified was sent a document listing the patient's current HRA therapy, the date of his or her last prescription refill, and the name and telephone number of the dispensing pharmacy. A letter summarized the literature; outlined the criteria used to identify candidate patients; gave the current indications, dosages, and average wholesale prices of the HRAs; and asked the prescriber to switch the patient to generic cimetidine. HRA use in an MCO that participated in the program was compared with HRA use in a nonparticipating MCO for the second quarter of 1994 (the baseline period), the fourth quarter of 1994, and the first quarter of 1995. The nonparticipating MCO showed no change between baseline and 1995 in the proportion of HRA prescriptions accounted for by brand-name and generic cimetidine combined (14% for each period). The average acquisition cost per HRA prescription remained about $75 for each study quarter. In the participating MCO, the proportion of HRA prescriptions accounted for by brand-name plus generic cimetidine increased from 18% at baseline to 39% in the first quarter of 1995. The average acquisition cost per HRA prescription fell from $71 at baseline to $65 in the first quarter of 1995. A program to shift the use of brand-name HRAs to generic cimetidine in MCOs successfully altered prescribing patterns and reduced expenditures for these agents.

Cimetidine↗

PubMed1996

A cell cycle-regulated bacterial DNA methyltransferase is essential for viability.

The CcrM adenine DNA methyltransferase, which specifically modifies GANTC sequences, is necessary for viability in Caulobacter crescentus. To our knowledge, this is the first example of an essential prokaryotic DNA methyltransferase that is not part of a DNA restriction/modification system. Homologs of CcrM are widespread in the alpha subdivision of the Proteobacteria, suggesting that methylation at GANTC sites may have important functions in other members of this diverse group as well. Temporal control of DNA methylation state has an important role in Caulobacter development, and we show that this organism utilizes an unusual mechanism for control of remethylation of newly replicated DNA. CcrM is synthesized de novo late in the cell cycle, coincident with full methylation of the chromosome, and is then subjected to proteolysis prior to cell division.

Alleles↗

PubMed1996

Bacterial differentiation: sizing up sporulation.

New results on Bacillus subtilis sporulation suggest that size differences between the post-septation compartments trigger differential gene expression, which is then coordinated by communication between the nascent mother cell and forespore compartments.

Bacillus subtilis↗

PubMed1996

DNA allelic alterations within VNTR loci of scleroderma families.

We have characterized genetic alterations at the molecular level in 49 scleroderma and 45 control families using variable number tandem repeats (VNTRs). Additionally, paired fibroblast cell lines from the 'affected' and 'unaffected' skin and peripheral blood leucocytes of 30 patients were also examined. All families in this study were typed for Class I Cw alleles and Class II-DRB, -DQA and -DQB to confirm family membership. There were significant rises in the level of VNTR mutations in scleroderma patients (36.7%, n = 18), their siblings (16.3%, n = 13) and offspring (21.7%, n = 15). The level of VNTR mutations in the control group was 0.6% (n = 5). These mutations did not correlate with the presence of autoantibodies and no patient was taking a known clastogenic drug. The most common VNTR site for mutation was pYNZ22 (17p13.4). Differences were also seen in the VNTR alleles between fibroblast and lymphocyte DNA from the same patient, as measured by size alteration of one of the alleles. We have found that VNTRs are unstable in scleroderma patients, relatives and offspring. The reason for the genomic changes remains unknown, but previous studies have implicated the presence of a clastogen.

Alleles↗

PubMed1996

A randomized phase I study of oral etoposide with or without granulocyte-macrophage colony-stimulating factor for the treatment of patients with advanced cancer.

The purpose of this study was to evaluate the feasibility of chronic oral administration of etoposide with granulocyte-macrophage colony-stimulating factor (GM-CSF) [sargramostim (Immunex)] coadministration or premedication; to estimate and compare the frequency of toxicities accompanying etoposide administration alone, etoposide/GM-CSF coadministration and etoposide with GM-CSF premedication. Thirty-nine patients with advanced treatment-refractory malignancies were enrolled to this study. Eligible patients were randomized to one of three treatment arms: daily oral etoposide alone for 21 days (arm A); daily oral etoposide for 21 days with GM-CSF, 250 micrograms/m2, s.c. twice daily for the first 10 days of etoposide administration (arm B); or daily oral etoposide for 21 days with GM-CSF twice daily for the sixth through second days preceding etoposide administration (arm C). Courses of treatment were repeated every 28 days. Etoposide dosages for each arm were 25, 50, 75 and 100 mg/m2/day. At least three patients were treated at each dosage level until dose-limiting toxicity was observed. Patients had twice weekly blood counts and weekly clinical examinations to assess toxicity. Patients with measurable or evaluable evidence of cancer were assessed for antitumor response after every other course of therapy. Nadir neutrophil counts at each dosage level were compared between treatment arms by non-parametric Wilcoxen rank sum tests. GM-CSF coadministration (arm B) or premedication (arm C) with daily chronic oral etoposide was feasible and did not lead to excessive hematological toxicity. Pairwise comparisons of neutrophil nadirs for the first course of therapy for each treatment arm did not demonstrate any significant differences and, at most, a slight trend favoring improved neutrophil nadirs was shown for arm C compared to arm A (p = 0.07). Dose intensity as measured by mean days of etoposide administered per patient for each arm suggested only slight improvement in etoposide tolerance for treatment arms B and C. The conclusion, GM-CSF can be safely administered to patients receiving chronic daily oral etoposide. It appears that GM-CSF provides no clinically useful improvement in granulocyte tolerance of therapy.

Administration, Oral↗