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Biomedical subjects

D A Jackson

Publications and source records attributed to D A Jackson.

At least 73 records · Page 4Linked to original sources
PubMed1994

Replication and transcription sites are colocalized in human cells.

HeLa cells synchronized at different stages of the cell cycle were permeabilized and incubated with analogues of nucleotide triphosphates; then sites of incorporation were immunolabeled with the appropriate fluorescent probes. Confocal microscopy showed that sites of replication and transcription were not diffusely spread throughout nuclei, reflecting the distribution of euchromatin; rather, they were concentrated in 'foci' where many polymerases act together. Transcription foci aggregated as cells progressed towards the G1/S boundary; later they dispersed and became more diffuse. Replication was initiated only at transcription sites; later, when heterochromatin was replicated in enlarged foci, these remained sites of transcription. This illustrates the dynamic nature of nuclear architecture and suggests that transcription may be required for the initiation of DNA synthesis.

Autoantigens↗
PubMed1994

Sites in human nuclei where DNA damaged by ultraviolet light is repaired: visualization and localization relative to the nucleoskeleton.

The repair of damage induced in DNA by ultraviolet light involves excision of the damage and then repair synthesis to fill the gap. We investigated the sites of repair synthesis using MRC-5 fibroblasts and HeLa cells in G1 phase. Cells were encapsulated in agarose microbeads to protect them during manipulation, irradiated, incubated to allow repair to initiate, and permeabilized with streptolysin O to allow entry of labelled triphosphates; [32P]dTTP was incorporated into acid-insoluble material in a dose-dependent manner. Incubation with biotin-16-dUTP allowed sites of incorporation to be indirectly immunolabeled using a FITC-conjugated antibody; sites were not diffusely spread throughout nuclei but concentrated in discrete foci. This is similar to sites of S phase activity that are attached to an underlying nucleoskeleton. After treatment with an endonuclease, most repaired DNA electroeluted from beads with chromatin fragments; this was unlike nascent DNA made during S phase and suggests that repaired DNA is not as closely associated with the skeleton. However, the procedure destroyed repair activity, so repaired DNA might be attached in vivo through a polymerase that was removed electrophoretically. Therefore this approach cannot be used to determine decisively whether repair sites are associated with a skeleton in vivo.

Cell Cycle↗
PubMed1994

Sites in human nuclei where damage induced by ultraviolet light is repaired: localization relative to transcription sites and concentrations of proliferating cell nuclear antigen and the tumour suppressor protein, p53.

The repair of damage induced in DNA by ultraviolet light involves excision of the damaged sequence and synthesis of new DNA to repair the gap. Sites of such repair synthesis were visualized by incubating permeabilized HeLa or MRC-5 cells with the DNA precursor, biotin-dUTP, in a physiological buffer; then incorporated biotin was immunolabeled with fluorescent antibodies. Repair did not take place at sites that reflected the DNA distribution; rather, sites were focally concentrated in a complex pattern. This pattern changed with time; initially intense repair took place at transcriptionally active sites but when transcription became inhibited it continued at sites with little transcription. Repair synthesis in vitro also occurred in the absence of transcription. Repair sites generally contained a high concentration of proliferating cell nuclear antigen but not the tumour-suppressor protein, p53.

Amanitins↗
PubMed1994

Replication factories and nuclear bodies: the ultrastructural characterization of replication sites during the cell cycle.

Sites of replication in synchronized HeLa cells were visualized by light and electron microscopy; cells were permeabilized and incubated with biotin-16-dUTP, and incorporation sites were immunolabelled. Electron microscopy of thick resinless sections from which approximately 90% chromatin had been removed showed that most DNA synthesis occurs in specific dense structures (replication factories) attached to a diffuse nucleoskeleton. These factories appear at the end of G1-phase and quickly become active; as S-phase progresses, they increase in size and decrease in number like sites of incorporation seen by light microscopy. Electron microscopy of conventional thin sections proved that these factories are a subset of nuclear bodies; they changed in the same characteristic way and contained DNA polymerase alpha and proliferating cell nuclear antigen. As replication factories can be observed and labelled in non-permeabilized cells, they cannot be aggregation artifacts. Some replication occurs outside factories at discrete sites on the diffuse skeleton; it becomes significant by mid S-phase and later becomes concentrated beneath the lamina.

Biotin↗
PubMed1993

Further follow up of mortality and incidence of cancer in men from the United Kingdom who participated in the United Kingdom's atmospheric nuclear weapon tests and experimental programmes.

OBJECTIVES: To study the long term effects of participation in the United Kingdom's atmospheric nuclear weapon tests and experimental programmes and to test hypotheses generated by an earlier report, including the possibility that participation in tests caused small hazards of leukaemia and multiple myeloma. DESIGN: Follow up study of mortality and cancer incidence. SUBJECTS: 21,358 servicemen and civilians from the United Kingdom who participated in the tests and a control group of 22,333 non-participants. MAIN OUTCOME MEASURES: Numbers of deaths; standardised mortality ratios; relative risks of mortality from all causes and 27 types of cancer. RESULTS: During seven further years of follow up the numbers of deaths observed in participants were fewer than expected from national rates for all causes, all neoplasms, leukaemia, and multiple myeloma (standardised mortality ratios 0.86, 0.85, 0.57, and 0.46); death rates were lower than in controls (relative risks 0.99, 0.96, 0.57, and 0.57; 90% confidence intervals all included 1.00). In the period more than 10 years after the initial participation in tests the relative risk of death in participants compared with controls was near unity for all causes (relative risk 0.99 (0.95 to 1.04) and all neoplasms (0.95 (0.87 to 1.04)); it was raised for bladder cancer (2.69 (1.42 to 5.20)) and reduced for cancers of the mouth, tongue, and pharynx (0.45 (0.22 to 0.93)) and for lung cancer (0.85 (0.73 to 0.99)). For leukaemia mortality was equal to that expected from national rates but greater than in controls for both the whole follow up period (1.75 (1.01 to 3.06)) and the period 2-25 years after the tests (3.38 (1.45 to 8.25)). CONCLUSION: Participation in nuclear weapon tests had no detectable effect on expectation of life or on subsequent risk of developing cancer or other fatal diseases. The excess of leukaemia in participants compared with controls seems to be principally due to a chance deficit in the controls, but the possibility that participation in the tests may have caused a small risk of leukaemia in the early years afterwards cannot be ruled out.

Environmental Exposure↗
PubMed1993

Visualization of replication factories attached to nucleoskeleton.

HeLa cells in early S phase were encapsulated in agarose microbeads, permeabilized, and incubated with biotin-11-dUTP in a "physiological" buffer. Sites of DNA synthesis were then immunolabeled. As others have found, approximately 150 focal sites of synthesis were visible in each nucleus by light microscopy; they also contained DNA polymerase alpha and proliferating cell nuclear antigen. Electron microscopy of thick resinless sections from which approximately 90% of the chromatin had been removed revealed a similar number of dense, morphologically discrete ovoid bodies strung along a nucleoskeleton. The ovoids remained morphologically and functionally intact despite the removal of most of the chromatin. After 2.5 min of incubation with biotin-11-dUTP, the incorporated analog was associated only with ovoids; after 5 min it began to spread into the adjacent chromatin, which became extensively labeled after 1 hr. This provides visual evidence for polymerization "factories" fixed to a skeleton, with replication occurring as the template moves through them.

Biotin↗
PubMed1993

Visualization of focal sites of transcription within human nuclei.

HeLa cells were encapsulated in agarose microbeads, permeabilized and incubated with Br-UTP in a 'physiological' buffer; then sites of RNA synthesis were immunolabelled using an antibody that reacts with Br-RNA. After extending nascent RNA chains by < 400 nucleotides in vitro, approximately 300-500 focal synthetic sites can be seen in each nucleus by fluorescence microscopy. Most foci also contain a component of the splicing apparatus detected by an anti-Sm antibody. alpha-amanitin, an inhibitor of RNA polymerase II, prevents incorporation into these foci; then, using a slightly higher salt concentration, approximately 25 nucleolar foci became clearly visible. Both nucleolar and extra-nucleolar foci remain after nucleolytic removal of approximately 90% chromatin. An underlying structure probably organizes groups of transcription units into 'factories' where transcripts are both synthesized and processed.

Cell Nucleolus↗
PubMed1993

Modulation of liver-specific transcription by interactions between hepatocyte nuclear factor 3 and nuclear factor 1 binding DNA in close apposition.

The liver-specific enhancer of the serum albumin gene contains an essential segment, designated eH, which binds the hepatocyte nuclear factor 3 alpha (HNF3 alpha) and ubiquitous nuclear factor 1/CCAAT transcription factor (NF1/CTF) proteins in tight apposition. We previously showed that activation of transcription by the eH site was correlated with an increase in intracellular HNF3 alpha levels during the in vitro differentiation of the hepatic cell line H2.35. We now show that transfection of an HNF3 alpha cDNA expression vector into dedifferentiated H2.35 cells is sufficient to induce transcription from the eH site. Mutational analysis of the enhancer demonstrates that NF1/CTF cooperates with HNF3 alpha to induce enhancer activity. However, when the eH site is removed from the context of the enhancer, NF1/CTF can inhibit transcriptional activation by HNF3 alpha. We conclude that the ternary complex of HNF3 alpha, NF1/CTF, and the eH site forms a novel, composite regulatory element that is sensitive to the local DNA sequence environment and suggest that the transcriptional stimulatory activity of NF1/CTF depends on its higher-order interactions with other proteins during hepatocyte differentiation.

Base Sequence↗
PubMed1993

Transcriptionally active minichromosomes are attached transiently in nuclei through transcription units.

Viral minichromosomes provide simple models for chromatin domains. The sequences attaching them to larger nuclear structures were mapped; attachments were defined operationally by their ability to prevent chromatin fragments electroeluting from nuclei. Cells encapsulated in agarose microbeads were lysed and analysed subsequently in a 'physiological' buffer. Non-transcribed minichromosomes eluted from nuclei but transcriptionally active ones did not. Cutting attached minichromosomes with HaeIII enabled most of the resulting approximately 400 bp fragments to elute. Analysis of residual fragments showed that no single sequence was responsible for attachment; rather, minichromosomes were attached at only one or two points through a promoter or part of a transcription unit. This suggests that RNA polymerases mediate attachments that change dynamically as the template slides past the attached enzyme. As, under optimal conditions, polymerases continue to elongate roughly at the rate found in vivo, these attachments are unlikely to be generated artifactually.

Animals↗
PubMed1993

Reflex sympathetic dystrophy syndrome: two case studies.

Reflex sympathetic dystrophy syndrome (RSDS) is a multisymptom, disabling disease that can involve peripheral nerve, muscle, bone, blood vessel and skin changes. Pain is the only common denominator among all patients. Two cases presented in this article describe patients with RSDS and demonstrate differences in symptoms and patient response. One treatment modality for RSDS is the stellate ganglion block, performed in the PACU by the anesthesiologist. Important postanesthesia nursing assessment parameters after this procedure are discussed.

Adult↗
PubMed1992

Mortality and occupational exposure to radiation: first analysis of the National Registry for Radiation Workers.

OBJECTIVE: To study cause specific mortality of radiation workers with particular reference to associations between fatal neoplasms and level of exposure to radiation. DESIGN: Cohort study. SETTING: United Kingdom. SUBJECTS: 95,217 radiation workers at major sites of the nuclear industry. MAIN OUTCOME MEASURE: Cause of death. RESULTS: Most standardised mortality ratios were below 100: 83 unlagged, 85 with a 10 year lag for all causes; 84 unlagged, 86 lagged for all cancers; and 80 for all known other causes, indicating a "healthy worker effect." The deficit of lung cancer (75 unlagged, 76 lagged) was significant at the 0.1% level. Standardised mortality ratios were significantly raised (214 unlagged, 303 lagged) for thyroid cancer, but there was no evidence for any trend with external recorded radiation dose. Dose of external radiation and mortality from all cancers were weakly correlated (p = 0.10), and multiple myeloma was more strongly correlated (p = 0.06); for leukaemia, excluding chronic lymphatic, the trend was significant (p = 0.03; all tests one tailed). The central estimates of lifetime risk derived from these data were 10.0% per Sv (90% confidence interval less than 0 to 24%) for all cancers and 0.76% per Sv (0.07 to 2.4%) for leukaemia (excluding chronic lymphatic leukaemia). These are, respectively, 2.5 times and 1.9 times the risk estimates recommended by the International Commission on Radiological Protection, but 90% confidence intervals are large and the commission's risk factors fall well within the range. The positive trend with dose for all cancers, from which the risk estimate was derived, was not significant. The positive association between leukaemia (except chronic lymphatic leukaemia) was significant and robust in subsidiary analyses. This study showed no association between radiation exposure and prostatic cancer. CONCLUSION: There is evidence for an association between radiation exposure and mortality from cancer, in particular leukaemia (excluding chronic lymphatic leukaemia) and multiple myeloma, although mortality from these diseases in the study population overall was below that in the general population. The central estimates of risk from this study lie above the most recent estimates of the International Commission on Radiological Protection for leukaemia (excluding chronic lymphatic leukaemia) and for all malignancies. However, the commission's risk estimates are well within the 90% confidence intervals from this study. Analysis of combined cohorts of radiation workers in the United States indicated lower risk estimates than the commission recommends, and when the American data are combined with our analysis the overall risks are close to those estimated by the commission. This first analysis of the National Registry for Radiation Workers does not provide sufficient evidence to justify a revision in risk estimates for radiological protection purposes.

Adult↗
PubMed1992

The attachments of chromatin loops to the nucleoskeleton.

It is widely assumed by cell biologists that chromatin is looped by attachment to some nuclear skeleton. 'Structural' attachments might be mediated through specific sequences; these would be attached in most cells in an organism, underlying the basic structure of the mitotic chromosome and persisting throughout interphase. 'Functional' attachments might also exist, perhaps if active polymerases are attached to the skeleton and replication and transcription occur as DNA is reeled through them. Cells of different tissues--and even cells of the same tissue--would have different attachments of this type. Problems associated with demonstrating these two kinds of attachment are discussed. We find little good evidence for 'structural' attachments and explore the idea that 'functional' attachments are the only kind that exist: 'functional' attachments involving active transcription units might be stable enough to organize chromatin during both interphase and mitosis, but 'dynamic' enough to allow duplication of attached sequences without disrupting loops.

Animals↗
PubMed1992

Weaning practices and breast-feeding duration in Northern Thailand.

Current infant feeding guidelines recommend exclusive breast-feeding until the infant is about 4 months old to reduce the risks of early termination of breast-feeding, undernutrition and infection. In many societies, however, supplementary foods are given well before 4 months of age. The present paper describes weaning practices, factors associated with early supplementation and the effects of supplementation on duration of breast-feeding in a random sample of sixty northern Thai breast-fed infants studied prospectively from birth to 2 years of age. Composition of supplementary foods, energy and protein intake from supplements and changes in the supplementary diet with increasing infant age are also described. Rice-based foods were given from soon after birth; 81% of the sample had received supplements by 6 weeks of age. Early supplementary feeding was significantly associated with rural residence, large household size, maternal employment in agriculture and maternal age. Girls and infants with lower birth weights tended to be supplemented earlier. Despite early feeding of supplements, breast-feeding was prolonged, with median duration of 12 months. Early introduction of supplements and quantity of supplements consumed in the first 3 months were not associated with duration of breast-feeding. However, mothers who gave infant formula as the first supplementary food stopped breast-feeding slightly earlier, as did younger mothers living in households with more children.

Breast Feeding↗
PubMed1992

Acetylcholine synthesis and release is enhanced by dibutyryl cyclic AMP in a neuronal cell line derived from mouse septum.

Cholinergic properties of the SN56.B5.G4 cell line derived from the fusion of neurons of the mouse postnatal day 21 septum and the murine neuroblastoma cell line N18TG2 were investigated and correlated with morphological differentiation. In basal serum-containing growth medium, few cells developed neurites. Neurite extension occurred in cells grown for 2 d with forskolin or dibutyryl cAMP (dbcAMP) but not with butyrate. In cells treated with these compounds, the activity of ChAT and ACh content were two- to threefold higher relative to controls. The cells synthesized ACh from choline taken up by the sodium-dependent high-affinity transport. Forskolin-, dbcAMP-, and butyrate-treated cells (but not the controls) were capable of spontaneous and depolarization-evoked ACh release. The results indicate that the morphological and the neurochemical aspects of SN56.B5.G4 cell differentiation are independently regulated.

Acetylcholine↗
PubMed1992

Ectopic pregnancy: a case study.

Ectopic pregnancy occurs when a fertilized egg implants on tissue other than the lining of the uterus. As the number of ectopic pregnancies increase, it is important that PACU nurses understand postoperative assessment and interventions for these women. Hypovolemic shock from preoperative and intraoperative bleeding is one potential problem for these patients that requires close postoperative monitoring. The case study of the ectopic pregnancy patient included with this article demonstrates important postanesthesia assessment parameters.

Adult↗
PubMed1991

Structure-function relationships in eukaryotic nuclei.

It may be that eukaryotic nuclei contain a collection of operationally independent units (genes), each controlled through its interactions with soluble protein factors which diffuse at random throughout the nucleoplasmic space. Alternatively, nuclei might be organized in such a sophisticated fashion that specific genes occupy distinct sites and that spatially ordered RNA synthesis, processing and transport delivers mature RNAs to predestined sites in the cytoplasm. Different fields of research support each of these extreme views. Molecular biologists inspecting the precise details of specific interactions, usually in vitro, inevitably favour the former, while cell biologists working with far more complicated systems generally assume that more elaborate arrangements exist. In considering the importance of nuclear architecture, I have attempted to relate a collection of experiments each of which intimates some close relationship between structural aspects of chromatin organization and the precise mechanisms underlying nuclear function. I will argue that higher-order structures are crucial for achieving the observed efficiency and coordination of many nuclear processes.

Animals↗
PubMed1991

Successful sustained lactation following postpartum tubal ligation.

This study was undertaken to see whether tubal ligation performed within days postpartum, and associated with a delay in the initiation of breastfeeding, exerts a disruptive influence on successfully establishing lactation among the rural population of northern Thailand. Lactational performance of 12 rural northern Thai mothers was not affected by the delay in reunion of mothers with their babies as a result of postpartum tubal sterilization procedure when compared with a group of 8 other healthy mothers and babies. The volume of breast milk transferred, frequency of breastfeeding and the total feeding time spent on the breast were similar on days 15, 45, 90, 180 and 360 postpartum. This finding suggests that the pattern of intense breastfeeding activity as practiced by this group of mothers has a stronger influence on prolonged and successful lactation than early contact in the immediate postpartum period.

Adult↗