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Biomedical subjects

F Hill

Publications and source records attributed to F Hill.

At least 55 records · Page 3Linked to original sources
PubMed1996

The Seismic Structure of the Sun

Global Oscillation Network Group data reveal that the internal structure of the sun can be well represented by a calibrated standard model. However, immediately beneath the convection zone and at the edge of the energy-generating core, the sound-speed variation is somewhat smoother in the sun than it is in the model. This could be a consequence of chemical inhomogeneity that is too severe in the model, perhaps owing to inaccurate modeling of gravitational settling or to neglected macroscopic motion that may be present in the sun. Accurate knowledge of the sun's structure enables inferences to be made about the physics that controls the sun; for example, through the opacity, the equation of state, or wave motion. Those inferences can then be used elsewhere in astrophysics.

Journal Article↗
PubMed1996

Differential Rotation and Dynamics of the Solar Interior

Splitting of the sun's global oscillation frequencies by large-scale flows can be used to investigate how rotation varies with radius and latitude within the solar interior. The nearly uninterrupted observations by the Global Oscillation Network Group (GONG) yield oscillation power spectra with high duty cycles and high signal-to-noise ratios. Frequency splittings derived from GONG observations confirm that the variation of rotation rate with latitude seen at the surface carries through much of the convection zone, at the base of which is an adjustment layer leading to latitudinally independent rotation at greater depths. A distinctive shear layer just below the surface is discernible at low to mid-latitudes.

Journal Article↗
PubMed1996

GONG Observations of Solar Surface Flows

Doppler velocity observations obtained by the Global Oscillation Network Group (GONG) instruments directly measure the nearly steady flows in the solar photosphere. The sun's differential rotation is accurately determined from single observations. The rotation profile with respect to latitude agrees well with previous measures, but it also shows a slight north-south asymmetry. Rotation profiles averaged over 27-day rotations of the sun reveal the torsional oscillation signal-weak, jetlike features, with amplitudes of 5 meters per second, that are associated with the sunspot latitude activity belts. A meridional circulation with a poleward flow of about 20 meters per second is also evident. Several characteristics of the surface flows suggest the presence of large convection cells.

Journal Article↗
PubMed1996

Characterization of a novel murine leukemia virus-related subgroup within mammals.

The murine leukemia virus (MuLV)-related retroviruses are one of seven genera which together constitute the family Retroviridae. They are widespread as both endogenous and exogenous agents within vertebrates and have been associated with a variety of malignancies and other disorders. We isolated and characterized 12 endogenous representatives of this genus from a number of mammalian hosts. Subsequent sequence analysis revealed that the isolated viruses cluster into two clearly distinct groups. All of the exogenous MuLV-related retroviruses which have been isolated to date, as well as several endogenous examples, fall into the first group, whereas the second group is represented solely by endogenous representatives, including human endogenous retrovirus type E (HERV.E). The two groups are widespread within mammals, with both often present within one animal species. Despite this, there is no evidence to date that recombination between members of the different groups has occurred. Genetic distances and several other properties of the HERV.E genome suggest that if exogenous members of this subgroup exist, they are likely to have biological properties different from those of the other exogenous viruses of this genus. Several of these viruses are known to have been integrated within their hosts' genomes for a long period of time, and a most recent divergence date for the MuLV and HERV.E subgroups can thus be proposed. This date, approximately 30 million years ago, is the most recent date possible, and it is probable that the actual period of time since their divergence is significantly longer.

Amino Acid Sequence↗
PubMed1996

PTL-1, a microtubule-associated protein with tau-like repeats from the nematode Caenorhabditis elegans.

Tau, MAP2 and MAP4 are structural microtubule-associated proteins (MAPs) that promote the assembly and stability of microtubules. They share three or four imperfect tandem repeats of an amino acid motif, which is involved in the binding to microtubules. All sequences to data containing this motif are of mammalian origin. We report here the cloning and functional characterisation of a new member of this family of proteins from the nematode Caenorhabditis elegans. This protein exists as two isoforms of 413 and 453 amino acids with four or five tandem repeats that are 50% identical to the tau/MAP2/MAP4 repeats. Both isoforms bind to microtubules and promote microtubule assembly, with the five-repeat isoform being more effective at promoting assembly than the four-repeat isoform. When expressed in COS cells, the five-repeat isoform co-localises with microtubules and induces the formation of microtubule bundles, whereas its expression in Sf9 cells leads to the extension of long unipolar processes. In view of its length, amino acid sequence and functional characteristics, we have named this invertebrate structural MAP 'Protein with Tau-Like Repeats' (PTL-1). In C. elegans PTL-1 is expressed in two places known to require microtubule function. It is first seen in the embryonic epidermis, when circumferentially oriented microtubules help to distribute forces generated during elongation. Later, it is found in mechanosensory neurons which contain unusual 15 protofilament microtubules required for the response to touch. These findings indicate that MAPs of the tau/MAP2/MAP4 family are found throughout much of the animal kingdom, where they may play a role in specialised processes requiring microtubules.

Amino Acid Sequence↗
PubMed1995

Easel, a gypsy LTR-retrotransposon in the Salmonidae.

Despite the close similarities between retroviruses and the gypsy/Ty3 group of LTR-retrotransposons their host ranges are largely distinct: the retroviruses are found only in vertebrates, whereas the gypsy LTR-retrotransposons are almost exclusively restricted to invertebrates, plants and fungi. Here we report the amplification by PCR, and characterisation, of one of the first LTR-retrotransposons to be discovered in vertebrates--in several members of the piscine family Salmonidae. Phylogenetic analysis of this retroelement, termed easel, indicates that it is probably a phylogeneticaly basal member of the gypsy group of LTR-retrotransposons and occurs in some of the same species from which retroviruses have previously been isolated. Thus some members of the Salmonidae are the first organisms known to harbour both retroviral branch elements and the gypsy LTR-retrotransposon branch elements. This creates an overlap in the host ranges of the two retroelement families.

Amino Acid Sequence↗
PubMed1995

3-Nitropyrrole and 5-nitroindole as universal bases in primers for DNA sequencing and PCR.

3-Nitropyrrole and 5-nitroindole have been assessed as universal bases in primers for dideoxy DNA sequencing and in the polymerase chain reaction (PCR). In contrast to a previous report, we have found that the introduction of more than one 3-nitropyrrole residue at dispersed positions into primers significantly reduced their efficiency in PCR and sequencing reactions. Primers containing 5-nitroindole at multiple dispersed positions were similarly affected; for both bases only a small number of substitutions were tolerated. In PCR experiments neither base, when incorporated into primers in codon third positions, was as effective as hypoxanthine, which was incorporated in six codon third positions in a 20mer oligomer. However, primers containing up to four consecutive 5-nitroindole substitutions performed well in both PCR and sequencing reactions. Consecutive 3-nitropyrrole substitutions were tolerated, but less well in comparable reactions.

Base Sequence↗
PubMed1995

A highly divergent retroviral sequence in the tuatara (Sphenodon).

Vertebrate retroviruses have been classified into a number of different genera, and although many mammalian and avian examples have been characterized, less information exists about the retroviruses present within other vertebrate classes. We designed oligonucleotide primers against two highly conserved motifs within retroviral protease and reverse transcriptase genes and used them to isolate a retroviral fragment from the reptile tuatara (Sphenodon). Sequence analysis of this element, termed SpeV, demonstrated that it is substantially different from previously reported viruses, and that it cannot easily be placed into any known retroviral genus. Furthermore SpeV suggests that there may be some major differences between the retroviral populations found in reptiles and those present in mammals and birds.

Amino Acid Sequence↗
PubMed1995

Dose-response curve for chromosome translocations measured in human lymphocytes exposed to 60Co gamma rays.

Chromosome painting was employed to measure frequencies of reciprocal translocations in human lymphocytes induced by 60Co gamma rays, with emphasis on low doses. Translocations and dicentrics were distinguished by use of a pan-centromeric probe. A total of 41,151 metaphases were analyzed at doses below 0.2 Gy. The linear "take-off" slope of the linear-quadratic dose-response curve for translocations, i.e., the alpha coefficient, was measured to be 0.023 +/- 0.005 translocations per cell per Gy. This alpha coefficient is more precise than previously measured. Because the alpha coefficient is the dominant contributor to the translocation frequency induced by low-level exposures, the results presented here will substantially reduce uncertainties in biodosimetry estimates obtained for stable translocations.

Biophysical Phenomena↗
PubMed1995

Management of traumatically displaced permanent incisors: the gentle touch.

This paper reports three cases where permanent incisor teeth had been displaced following trauma. Owing to the circumstances at presentation the cases were not treated according to the usual recommendations. However, the final outcome in each case was excellent. These observations indicate that a prospective clinical trial is needed.

Child↗
PubMed1994

Discrimination between leukaemia and non-leukaemia-related chromosomal abnormalities in the patient's lymphocytes.

The inability to measure precancer-related genetic damage accurately in blood cells of patients with leukemia or lymphoma has prevented the use in such patients of available biodosimetric methods to determine prior exposure to clastogenic agents. This is because a substantial amount of disease-related genetic damage appears in the blood cells of these patients, thus masking genetic damage that may have been caused prior to the disease. We describe a new approach that may be used to measure precancer-related chromosomal aberrations in such patients by totally separating the affected T lymphocytes from the malignant B lymphocytes. The approach employs stable chromosome translocations and will detect prior exposures above the detection limit of approximately 0.05-0.1 Gy. The utility of this approach is illustrated by using blood lymphocytes from a nuclear dockyard worker who claims his B cell leukaemia was induced by work-related radiation exposures. Blood lymphocytes were obtained after diagnosis of the disease, but prior to therapy, and measurements were made of the frequency of chromosomal abnormalities in PHA-stimulated lymphocytes without prior separation of T and B cells and in T lymphocytes after complete separation from B cells using a rosetting technique. Results show that the separation of T cells prior to PHA stimulation eliminates the cancer-related chromosomal damage and thus appears to facilitate biodosimetry of pre-cancer exposures in such patients.

Adult↗
PubMed1994

A mammalian homologue of Drosophila heterochromatin protein 1 (HP1) is a component of constitutive heterochromatin.

The Drosophila HP1 gene contains a highly conserved sequence, the chromobox, which can be used to isolate HP1-like genes from both mouse (M31 and M32) and man (HSM1) (Singh et al., 1991). Here we report that a monoclonal antibody (MoAb) raised against the M31 protein recognises a 26-kDa protein in murine and human nuclear extracts and localises to large masses of condensed chromatin within murine interphase nuclei, some of which are associated with the nucleoli. At metaphase, the MoAb binds to the centromeres of both human and murine chromosomes. The evolutionary conservation of this chromosomal localisation indicates that the M31 protein is likely to be important in the packaging of mammalian chromosomal DNA into constitutive heterochromatin.

3T3 Cells↗
PubMed1993

HIV/AIDS education in further education: a survey.

This paper summarizes a report prepared for the Health Education Authority on the nature and extent of HIV/AIDS education in further education (FE) for the 16-19 age range. The results are based on a questionnaire survey of all the FE and tertiary colleges in England which was carried out by the authors in 1990. The main conclusion is that, although most colleges claim to be making some provision for HIV/AIDS education, such provision varies considerably, tends to be voluntary and, moreover, reaches very few students. Some factors do seem to enhance HIV/AIDS education, such as the appointment of a coordinator and the provision of in-service training, but many FE staff seem to question whether it is their role to provide education of such a non-specialist nature.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Acceptance of mementos of fetal and perinatal loss in a south Australian population.

A package of mementos of a fetal or perinatal loss has been shown to help with the grieving process. The level of acceptance and the factors influencing acceptance of these mementos in a South Australian population was examined over a 27-month period. Data were available on 447 women and the acceptance rate was 79.6%. Major influences on the acceptance of mementos were maternal age and gestational age. Mothers in the 20-30 year age group were more likely to accept mementos than younger and older mothers. This age-related effect was more noticeable among genetic terminations and neonatal deaths than among spontaneous abortions or stillbirths. Memento acceptance of miscarriages and stillbirths over 20 weeks' gestation was significantly greater than for younger gestation. These findings may have an impact on the psychosocial management of perinatal loss. The high level of acceptance of these mementos is encouraging and vindicates our current practice which we recommend to others involved in the management of perinatal loss.

Australia↗
PubMed1993

Dosing regimens for spinal and epidural anesthesia.

Spinal anesthesia has proven to be a reliable and safe technique of major conduction anesthesia for nearly a century. Epidural anesthesia is being used for a multitude of applications in the operating room, labor and delivery setting, and more for the relief of postoperative analgesia. It is also noted that a growing number of nurse anesthetists are expanding their expertise in regional anesthesia to include continuous spinal, spinal techniques for infants, and epidural anesthesia techniques. This article reviews the physiological and pharmacological factors influencing the choice of anesthetic agents for major conduction anesthesia and the suggested dosing regimens.

Anesthesia, Epidural↗
PubMed1992

Inhibition of human immunodeficiency virus and growth of infected T cells by the immunosuppressive drugs cyclosporin A and FK 506.

The effects of the immunosuppressive drugs cyclosporin A and FK 506 were studied on cells chronically infected with human immunodeficiency virus type 1 (HIV-1) as well as on uninfected and newly infected cells. When cells chronically infected with HIV-1 or with HIV-2 were cocultivated with uninfected cells in the presence of cyclosporin A or FK 506 there was a delay in the formation of syncytia and of cytopathic effects. This inhibitory effect was not due to decreased membrane expression of CD4. In addition, there was an approximately 100-fold reduction in the yield of infectious HIV-1 when the infected cells were grown in the presence of these drugs, a finding consistent with other evidence of decreased HIV expression. Both drugs were found to inhibit the growth of chronically infected cells at concentrations that did not inhibit the growth of the uninfected cells. These results, demonstrating that cyclosporin A and FK 506 interfere with HIV production and selectively inhibit the growth of infected cells, suggest that they may be useful in the treatment of this infection and indicate further cellular targets for antiviral agents.

CD4 Antigens↗