Biomedical subjects

S Childs

Publications and source records attributed to S Childs.

At least 19 recordsLinked to original sources

PubMed2006

Effects of interventions aimed at changing the length of primary care physicians' consultation.

BACKGROUND: Observational studies have shown differences in process and outcome between the consultations of primary care physicians whose average consultation lengths differ. These differences may be due to self selection. OBJECTIVES: To assess the effectiveness and efficiency of interventions to alter the length of primary care physicians' consultations. SEARCH STRATEGY: The following electronic databases were searched: Cochrane Effective Practice and Organisation of Care Group (EPOC) Specialised Register (October 2002); CENTRAL (The Cochrane Library June 2003); MEDLINE (1966 to October 2002);EMBASE (1981 to October 2002); NHS National Research Register (June 2003). The search strategies combined subject terms for 'general practice', 'consultation' and 'length' with methodological filters. SELECTION CRITERIA: Randomised controlled trials (RCTs) and controlled clinical trials (CCTs) of interventions to alter the length of primary care physicians' consultations. DATA COLLECTION AND ANALYSIS: Data were extracted independently by two authors using agreed criteria. Disagreements were resolved by discussion. Where data were missing attempts were made to contact authors. Given the heterogeneity of studies meta-analysis was not attempted, and results are presented as a narrative summary. MAIN RESULTS: Six articles describing four UK trials met the inclusion criteria. All tested short term changes in the consultation time allocated to each patient and all had methodological weaknesses, particularly due to non-random allocation of patients. Altering appointment length resulted in modest changes in average length of consultation. There were no consistent differences in problem recognition, examination, prescribing, referral or investigation rates. There was some evidence that blood pressure was checked and smoking discussed more often when more time was available. None of the interventions were associated with differences in patient satisfaction. No trials examined efficiency. AUTHORS' CONCLUSIONS: The findings of this review do not provide sufficient evidence to support or resist a policy of altering the lengths of primary care physicians' consultations. Further trials are needed that focus on health outcomes and cost effectiveness.

Appointments and Schedules↗

PubMed2004

Systematic review: the effect of Helicobacter pylori and its eradication on gastro-oesophageal reflux disease in patients with duodenal ulcers or reflux oesophagitis.

BACKGROUND: The effect of Helicobacter pylori in provoking or protecting against gastro-oesophageal reflux disease is unclear and studies have given conflicting results. Recent guidelines recommend H. pylori eradication in patients on long-term proton pump inhibitors. AIM: To ascertain the effect of H. pylori eradication on gastro-oesophageal reflux disease outcomes (reflux oesophagitis and heartburn) in patients with duodenal ulcer disease, and to ascertain the effect of H. pylori infection on reflux oesophagitis concerning heartburn, pH, severity, healing and relapse rates. METHODS: A systematic review of electronic databases was undertaken to September 2003. Experts in the field, pharmaceutical companies and journals were contacted about unpublished trials. Studies were reviewed according to predefined eligibility and quality criteria. Twenty-seven studies/trials were included in the systematic review. RESULTS: Study variation rather than therapy-influenced results in relation to the presence or absence of oesophagitis in patients with duodenal ulcer who underwent H. pylori eradication at 6-48 months follow-up. In patients with reflux oesophagitis no obvious differences were discovered in heartburn scores, 24-h pH values, healing and relapse rates between H. pylori-positive and -negative cases. CONCLUSION: There is no evidence to indicate that H. pylori eradication in duodenal ulcer disease provokes reflux oesophagitis or worsens heartburn; (ii) there are insufficient data to draw firm conclusions about the impact of H. pylori in patients with reflux oesophagitis.

Duodenal Ulcer↗

PubMed2003

Fibroblast reaction to island topography: changes in cytoskeleton and morphology with time.

In order to develop next-generation tissue engineering materials, the understanding of cell responses to novel material surfaces needs to be better understood. Topography presents powerful cues for cells, and it is becoming clear that cells will react to nanometric, as well as micrometric, scale surface features. Polymer-demixing of polystyrene and polybromostyrene has been found to produce nanoscale islands of reproducible height, and is very cheap and fast compared to techniques such as electron beam lithography. This study observed temporal changes in cell morphology and actin and tubulin cytoskeleton using scanning electron and fluorescence microscopy. The results show large differences in cell response to 95 nm high islands from 5 min to 3 weeks of culture. The results also show a change in cell response from initial fast organisation of cytoskeleton in reaction to the islands, through to lack of cell spreading and low recruitment of cell numbers on the islands.

Actins↗

PubMed2001

Gridlock signalling pathway fashions the first embryonic artery.

Arteries and veins are morphologically, functionally and molecularly very different, but how this distinction is established during vasculogenesis is unknown. Here we show, by lineage tracking in zebrafish embryos, that angioblast precursors for the trunk artery and vein are spatially mixed in the lateral posterior mesoderm. Progeny of each angioblast, however, are restricted to one of the vessels. This arterial-venous decision is guided by gridlock (grl), an artery-restricted gene that is expressed in the lateral posterior mesoderm. Graded reduction of grl expression, by mutation or morpholino antisense, progressively ablates regions of the artery, and expands contiguous regions of the vein, preceded by an increase in expression of the venous marker EphB4 receptor (ephb4) and diminution of expression of the arterial marker ephrin-B2 (efnb2). grl is downstream of notch, and interference with notch signalling, by blocking Su(H), similarly reduces the artery and increases the vein. Thus, a notch-grl pathway controls assembly of the first embryonic artery, apparently by adjudicating an arterial versus venous cell fate decision.

Animals↗

PubMed2000

Zebrafish dracula encodes ferrochelatase and its mutation provides a model for erythropoietic protoporphyria.

Exposure to light precipitates the symptoms of several genetic disorders that affect both skin and internal organs. It is presumed that damage to non-cutaneous organs is initiated indirectly by light, but this is difficult to study in mammals. Zebrafish have an essentially transparent periderm for the first days of development. In a previous large-scale genetic screen we isolated a mutation, dracula (drc), which manifested as a light-dependent lysis of red blood cells [1]. We report here that protoporphyrin IX accumulates in the mutant embryos, suggesting a deficiency in the activity of ferrochelatase, the terminal enzyme in the pathway for heme biosynthesis. We find that homozygous drc(m248) mutant embryos have a G-->T transversion at a splice donor site in the ferrochelatase gene, creating a premature stop codon. The mutant phenotype, which shows light-dependent hemolysis and liver disease, is similar to that seen in humans with erythropoietic protoporphyria, a disorder of ferrochelatase.

Animals↗

PubMed2000

M-ABC2, a new human mitochondrial ATP-binding cassette membrane protein.

We have isolated a human cDNA encoding a novel ATP-binding cassette (ABC) protein whose gene was previously localized to chromosome 1q42 [Allikmets et al. (1995) Mamm. Genome 6, 111-117]. The gene transcript is expressed in all human tissues examined, with the highest levels in bone marrow. A non-expressed pseudogene also exists at chromosome 15q13-14. The new protein, which is most similar to the mitochondrial (M)-ABC1 protein, was also localized to mitochondria and therefore designated 'M-ABC2'. The N-terminus of M-ABC2 was shown to contain a mitochondrial-targeting signal sequence.

ATP-Binding Cassette Transporters↗

PubMed2000

Characterization of ABCB9, an ATP binding cassette protein associated with lysosomes.

We have cloned full-length human and mouse cDNAs of ABCB9, which encodes a predicted multiple-spanning transmembrane domain and a nucleotide-binding domain with Walker motifs. It is therefore designated as a "half" ATP binding cassette (ABC) transporter. Northern analysis shows that the ABCB9 mRNA is expressed at a high level in testes and moderate levels in brain and spinal cord. A splice variant mRNA deleted in the last pair of predicted transmembrane segments was shown to be expressed in human tissues. Phylogenetic analysis indicates that ABCB9 is closely related to TAP1 and TAP2, two "half" ABC proteins found in endoplasmic reticulum. ABCB9 protein colocalized with the lysosomal markers, LAMP1 and LAMP2, in transfected cells. ABCB9 protein appears to be most highly expressed in the Sertoli cells of the seminiferous tubules in mouse and rat testes. These cells have high levels of phagocytosis and secretory activities. These findings pave the way for further investigation into the potential novel function of ABCB9 in lysosomes.

ATP-Binding Cassette Transporters↗

PubMed2000

The management of Helicobacter pylori infection in primary care: a systematic review of the literature.

OBJECTIVE: The aim of the present study was to provide evidence from the literature to inform the production of guidelines by the European Society for Primary Care Gastroenterology (ESPCG) for the management of Helicobacter pylori infection in primary care. METHODS: A systematic review was conducted, searching MEDLINE, EMBASE and the Cochrane Library. The systematic review was designed to answer a number of question: the role of H.pylori in the aetiology of peptic ulcer disease (PUD), gastric cancer (GC), non-ulcer dyspepsia (NUD) and oesophagitis; non-invasive testing for H.pylori and post-treatment testing; eradication therapy; and cost issues. Selection of records concentrated on the highest quality studies, i.e. systematic reviews, meta-analyses and cost analyses. RESULTS: Helicobacter pylori infection is a causal factor in PUD and GC but not in NUD or oesophagitis. Serological tests and urea breath tests (UBTs) can be used for the detection of H.pylori, but UBT is the preferred choice for post-treatment testing. Proton pump inhibitor (PPI)-based triple regimens are the preferred eradication therapy. Eradication therapy is more cost-effective than long-term maintenance therapy. CONCLUSIONS: Strong evidence is available for answering questions on the aetiology of stomach ulcers and GU, eradication therapies and cost issues. Weaker evidence is available for answering the questions on the aetiology of NUD and non-invasive testing. No evidence is available for answering the question on the role of H.pylori in the aetiology of oesophagitis.

Anti-Bacterial Agents↗

PubMed1998

Taxol resistance mediated by transfection of the liver-specific sister gene of P-glycoprotein.

The sister gene of P-glycoprotein (Spgp) is a liver-specific ATP-binding cassette protein highly related to the P-glycoprotein (Pgp) family (S. Childs et al, Cancer Res., 55: 2029-2034, 1995). Spgp appears to be related to the Pgp family by an ancient duplication occurring before the division of fish and mammals. P-Glycoproteins have diverse functions including broad specificity multidrug resistance in cell lines and tumors, detoxification of tissues such as the intestine and blood-brain barrier, and phosphatidylcholine transport in liver. Spgp is a Mr approximately 170,000 glycosylated plasma membrane protein localized to the canalicular surface of hepatocytes in the rat liver. The full-length cDNA of Spgp was isolated from rat, and its expression was characterized in situ and in transfected cells. The expression of Spgp correlates with the differentiation of hepatocytes and is seen only in late liver development. It is not observed in hepatoma cell lines. The physiological function of Spgp in liver is unknown, but it maps to 2q31 in humans, in the vicinity of liver transport disorders for bile acids and cholesterol. Spgp may therefore be involved in some aspect of bile acid or cholesterol metabolism. Spgp transfectants have a low level resistance to Taxol but not to other drugs that form part of the multidrug resistance phenotype. This resistance is reversible by the Pgp-reversing agents cyclosporin A, PSC833, and verapamil, suggesting a conservation in some functions of Pgps across large evolutionary distance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1998

Up-regulation of the multidrug resistance genes, Mrp1 and Mdr1b, and down-regulation of the organic anion transporter, Mrp2, and the bile salt transporter, Spgp, in endotoxemic rat liver.

Endotoxin-induced cholestasis is mainly caused by an impaired canalicular secretion. Mrp2, the canalicular multispecific organic anion transporter, is strongly down-regulated in this situation, and canalicular bile salt secretion is also reduced. We hypothesized that other adenosine triphosphate-binding cassette (ABC) transporters may compensate for the decreased transport activity to protect the cell from cytokine-induced oxidative damage. Therefore, we examined the expression of ABC-transport proteins in membrane fractions of whole liver and of isolated hepatocytes of endotoxin-treated rats and performed reverse-transcriptase polymerase chain reaction (RT-PCR) on mRNA isolated from these livers. In addition, the localization of these transporters was examined using confocal scanning laser microscopy. By 6 hours after endotoxin administration, we found a clear increase of mrp1 mRNA and protein, whereas mrp2 mRNA and protein were decreased. This was confirmed in isolated hepatocytes. In addition, mdr1b mRNA was strongly increased, whereas mdr1a and mdr2 mRNA did not change significantly. Both the mRNA and protein levels of the sister of P-glycoprotein (spgp), the recently cloned bile salt transporter, decreased. After endotoxin treatment, the normally sharply delineated canalicular staining of mrp2 and spgp had changed to a fuzzy pattern, suggesting localization in a subapical compartment. We conclude that endotoxin-induced cholestasis is caused by decreased mrp2 and spgp levels, as well as an abnormal localization of these proteins. The simultaneous up-regulation of mrp1 and mdr1b may confer resistance to hepatocytes against cytokine-induced metabolic stress.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1998

Results of a multicenter trial of the CapSure (Re/Stor) Continence shield on women with stress urinary incontinence.

OBJECTIVES: To prospectively study the impact of the CapSure (Re/Stor) Continence shield for the treatment of stress urinary incontinence. METHODS: One hundred women with pure stress urinary incontinence were enrolled in a 6-month study. Objective measures of urine loss included pad weight test (PdWt) and provocative stress test (PST). Subjective measures included incontinence diaries documenting the number of incontinence episodes per day (IEPD), quality of life questionnaires, and satisfaction surveys. Objective and subjective measures were performed prior to enrollment, during use of the CapSure shield, and after discontinuation of the device. RESULTS: During the 12-week device utilization period, PdWt measurements demonstrated a 96% reduction in urine loss by week 1 and 97% by week 12. Eighty-two percent of subjects were completely dry by week 12. PST demonstrated 100% reduction in urine loss at each visit, with 91% of subjects completely dry by week 12. IEPD also demonstrated a 91% reduction in incontinence episodes by week 12. Quality of life scores and patient satisfaction surveys demonstrated significant improvement. During the 6-week post device utilization period (PUP), subjects continued to demonstrate a reduction in urine loss compared to pre-enrollment data, despite discontinuation of use. PdWt measurements demonstrated a 73% and 79% reduction in urine loss at weeks 14 and 18, respectively. Measurements of PST and IEPD demonstrated significant reductions in urine loss at weeks 14 and 18. A 1.5% prevalence of positive urine cultures was noted during device use. Bothersome vaginal or urethral irritation occurred in 12% of patients. Adverse events were few and required no therapeutic intervention. CONCLUSIONS: The CapSure shield is a safe and efficacious method of managing stress urinary incontinence in women.

Adult↗

PubMed1998

A gene encoding a liver-specific ABC transporter is mutated in progressive familial intrahepatic cholestasis.

The progressive familial intrahepatic cholestases (PFIC) are a group of inherited disorders with severe cholestatic liver disease from early infancy. A subgroup characterized by normal serum cholesterol and gamma-glutamyltranspeptidase (gammaGT) levels is genetically heterogeneous with loci on chromosomes 2q (PFIC2) and 18q. The phenotype of the PFIC2-linked group is consistent with defective bile acid transport at the hepatocyte canalicular membrane. The PFIC2 gene has now been identified by mutations in a positional candidate, BSEP, which encodes a liver-specific ATP-binding cassette (ABC) transporter, sister of p-glycoprotein (SPGP). The product of the orthologous rat gene has been shown to be an effective bile acid transporter in vitro. These data provide evidence that SPGP is the human bile salt export pump (BSEP).

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1996

Characterization and epitope mapping of several new anti-P-glycoprotein monoclonal antibodies.

Monoclonal antibodies (MAbs) were raised against partially purified Class I P-glycoprotein from multidrug-resistant Chinese hamster ovary CHRB30 cells. Fifteen stable monoclonal hybridoma cell lines were established, and the secreted antibodies were classified into 8 groups on the basis of banding pattern on immunoblots of P-glycoprotein digested with cyanogen bromide or partially digested with proteases. One representative of each group was tested further for several activities. Six of the 8 recognized human P-glycoprotein in the multidrug-resistant SKVLBI cell line. None of the antibodies recognized P-glycoprotein in unfixed cells, suggesting that all recognize cytoplasmic epitopes or extracellular epitopes not accessible in native P-glycoprotein. All 8 antibodies were able to immunoprecipitate P-glycoprotein from non-denaturing detergent solution. The linear epitopes of the antibodies were mapped to 11-27 amino acids. Two of the antibodies had epitopes in the linker region, 3 in the N-terminal nucleotide binding domain, 2 in the C-terminal nucleotide binding domain and 1 in the predicted cytoplasmic loop between predicted transmembrane helices 8 and 9. These antibodies, with known epitopes, could have uses for P-glycoprotein detection, structure/function studies, purification and quantitation.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1996

Treatment of urinary tract infections: selecting an appropriate broad-spectrum antibiotic for nosocomial infections.

Clinical and in vitro data indicate that cefepime, a fourth-generation cephalosporin, may be a valuable addition in the treatment of serious infections. In this study, hospitalized patients with complicated and uncomplicated urinary tract infection (UTI), for which parenteral therapy was appropriate, were enrolled in a 2:1 ratio open, randomized trial comparing the efficacy and safety of cefepime and ceftazidime. A total of 180 patients, including 6 with concurrent bacteremia, were evaluated for their response to cefepime (n = 118) or ceftazidime (n = 62), both of which were administered by intravenous infusion or intramuscular injection in doses of 500 mg every 12 hours. In cases of complicated UTI, cefepime produced a satisfactory clinical response in 83 of 93 (89%) patients and eradicated 83 of 98 (85%) pathogens. A satisfactory clinical response to ceftazidime was experienced by 43 of 50 (86%) patients; and in 39 of 50 (78%) cases pathogens were eradicated. In uncomplicated cases, the clinical response and bacterial eradication rates for cefepime were 23 of 25 (92%) and 22 of 26 (85%), respectively, and for ceftazidime 12 of 12 (100%) and 11 of 12 (92%). Of the 6 patients with concomitant bacteremia, 5 received cefepime and 1, ceftazidime. The infecting organisms, Escherichia coli and Proteus mirabilis, were eradicated in all cases, although one cefepime-treated patient had an unsatisfactory clinical response. The most common adverse events in both groups were headache, diarrhea, and vomiting; most events were unrelated to therapy. Adverse events forced only a 2% withdrawal of patients in either group. There was local tolerance to both agents, and abnormalities in laboratory values were judged to be clinically insignificant. The results of this study indicate that cefepime can be used safely and successfully to treat both complicated and uncomplicated nosocomial infection of the urinary tract, including cases associated with concurrent bacteremia. Moreover, its safety profile appears comparable to those of other cephalosporins, and local tolerance is similar to that of ceftazidime. No patient in either group required discontinuation of therapy because of local intolerance at the infusion or injection site.

Bacteremia↗

PubMed1996

Duplication and evolution of the P-glycoprotein genes in pig.

The P-glycoproteins (Pgp's) are a small family of proteins frequently associated with the multidrug resistance phenotype in drug-selected cell lines. The number of Pgp isoforms in different mammalian species is variable although the reason for having a larger or smaller number of isoforms is not known. Two isoform classes from human, and three from rodents have been extensively characterised and have been shown to have independent expression patterns and substrate preferences. We have cloned 3' terminal genomic fragments for five members of the Pgp multigene family from the pig, which is the largest number of Pgp genes found in any mammalian species to date. Sequential duplications of one class of Pgp gene have given rise to this large gene family since four genes show similarity to the drug resistance-causing Class I isoform of Pgp. The fifth pig Pgp gene shows similarity to the phosphatidylcholine-translocating Class III isoform. The history of the duplications creating this large gene family can be traced by atypical features which have been inherited in common. These include a mutation in the stop codon at the 3' end of four Class I Pgp genes, increasing the coding region by six amino acids, and a SINE element of the PRE1 family inserted into the 3' untranslated region of three Class I Pgp's. We demonstrate expression of Class I pgp in pig brain cultured capillary endothelial cells, and Class III pgp in the liver, two important sites of expression of Pgp in rodents and humans. Thus there appears to be strong phylogenetic conservation in mammals of both sequence and expression of these two Pgp isoforms.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1995

Identification of a sister gene to P-glycoprotein.

The P-glycoproteins (Pgps) are a small family of transport proteins associated with the multidrug resistance phenotype of cell lines selected for growth in cytotoxic drugs. Utilizing low stringency screening, we have identified a novel gene closely related to the Pgps expressed in the pig and other mammalian liver which we have called Sister of P-glycoprotein (spgp). Sequence of this gene shows it to be a member of the ATP-binding cassette family of transporters and the gene most closely related to Pgp identified to date. The function of spgp is not known, but it can be recognized by at least one Pgp mAb, C219. This cross-reactivity has implications for expression studies in tissues and tumors utilizing this and other Pgp antibodies.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1995

A prospective randomized comparison of transurethral resection to visual laser ablation of the prostate for the treatment of benign prostatic hyperplasia.

OBJECTIVES: Transurethral resection of the prostate (TURP) represents the accepted standard of surgical therapy for the management of symptomatic bladder outlet obstruction due to benign prostatic hyperplasia (BPH). However, this is a major operative procedure associated with significant perioperative morbidity. Visual laser ablation of the prostate (VLAP) utilizing a neodymium:yttrium-aluminum-garnet laser represents a new technologic approach to the surgical management of BPH. We compared the relative safety and efficacy of these two surgical approaches in a prospective, randomized trial. METHODS: At 6 investigational sites in the United States, 115 men with symptomatic BPH more than 50 years of age and not in retention, were randomly assigned to undergo either TURP (59 patients) of VLAP (56 patients). VLAP patients received a mean of 10,200 J of energy delivered in a mean of 5.5 intraprostate laser applications. At preoperative baseline, 3 months, 6 months, and 1 year postoperatively, all patients underwent clinical evaluations, including ultrasonic prostatic volume determination, standardized American Urological Association (AUA)-6 symptom score, peak urine flow, postvoid residual urine volume, and quality-of-life assessment. RESULTS: Compared to TURP, the VLAP procedure required less time (23.4 versus 45.2 minutes; P < 0.01) and shorter hospitalization (1.8 versus 3.1 days, P < 0.01). VLAP was associated with a significantly lower rate of serious treatment-related complications compared to TURP (10.7% versus 35.6%; P < 0.01). Only One (2.2%) patient undergoing VLAP experienced a greater than 2.2 g/dL decrease in hemoglobin compared to 40% of TURP patients (P = 0.01). No patient in the VLAP group required blood transfusion compared with 3.4% of those undergoing TURP. Of the 115 patients, clinical outcomes measured at 1 year showed a mean improvement in AUA-6 symptom scores of -9.0 for VLAP compared with -13.3 for TURP (P < 0.04), mean increase in peak urinary flow rate of 5.3 cc/s for VLAP compared with 7.0 cc/s for TURP (P = 0.27), and mean decrease in postvoid residual urine volume of -55.4 cc for VLAP compared with -138.8 cc for TURP (P < 0.01). At 1 year, 78.2% of patients undergoing VLAP indicated that their quality of life was improved compared with 93.0% of patients undergoing TURP (P = 0.03). When compared with TURP, treatment of BPH with VLAP is associated with less hemoglobin decrease, a lower likelihood of serious complication, and requires less procedure time and a shorter hospital stay. Through a 1-year follow-up, VLAP produced significant improvement over baseline in objective and subjective outcome measures. However, for 1-year improvement in AUA-6 symptom score, postvoid residual urine volume, and quality of life, VLAP was less effective than TURP. CONCLUSIONS: In this initial study in the United States, with relatively low-energy laser applications, VLAP did not result in as complete a removal of prostatic tissue as did TURP. Considering the lower morbidity, shorter procedure and hospitalization times, and the degree of effectiveness that was achieved even at the low-energy doses used in this study, VLAP appears to be a viable and safe alternative to standard TURP.

Aged↗

PubMed1994

The Drosophila dorsal morphogen represses the tolloid gene by interacting with a silencer element.

The dorsal protein (DL) regulates the transcriptional activity of several genes that determine cell fate along the dorsoventral axis of the Drosophila melanogaster embryo. DL is present at high levels in ventral nuclei, where it activates some genes (twi and sna) and represses others (zen, dpp, and tld). DL shows homology to the Rel family of proteins and interacts with specific DNA sequences in the regulatory regions of its target genes. The distal portion of the zen gene acts as a silencer that can mediate the repression of a heterologous promoter in ventral regions of the embryo. It contains four DL binding sites which alone are sufficient for activation but not repression. Here we analyze the interaction of DL with another one of its repressed targets, the tolloid (tld) gene. Approximately 800 bp of 5'-flanking sequences upstream of the tld coding region were shown to drive an expression pattern indistinguishable from the wild-type pattern. A 423-bp fragment located within these sequences contains two DL binding sites and was shown to act as a silencer to mediate ventral repression. Point mutations in the sites abolish not only DNA binding but also ventral repression. We discuss a comparison of the DNA sequences from the zen and tld promoters and the possible mechanisms of transcriptional silencing.

Animals↗