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Biomedical subjects

R Law

Publications and source records attributed to R Law.

At least 19 recordsLinked to original sources
PubMed1995

Evolutionary cycling in predator-prey interactions: population dynamics and the red queen.

This paper describes the coevolution of phenotypes in a community comprising a population of predators and of prey. It is shown that evolutionary cycling is a likely outcome of the process. The dynamical systems on which this description is based are constructed from microscopic stochastic birth and death events, together with a process of random mutation. Births and deaths are caused in part by phenotype-dependent interactions between predator and prey individuals and therefore generate natural selection. Three outcomes of evolution are demonstrated. A community may evolve to a state at which the predator becomes extinct, or to one at which the species coexist with constant phenotypic values, or the species may coexist with cyclic changes in phenotypic values. The last outcome corresponds to a Red Queen dynamic, in which the selection pressures arising from the predator-prey interaction cause the species to evolve without ever reaching an equilibrium phenotypic state. The Red Queen dynamic requires an intermediate harvesting efficiency of the prey by the predator and sufficiently high evolutionary rate constant of the prey, and is robust when the model is made stochastic and phenotypically polymorphic. A cyclic outcome lies outside the contemporary focus on evolutionary equilibria, and argues for an extension to a dynamical framework for describing the asymptotic states of evolution.

Animals↗
PubMed1995

Effects of interleukin-1 and interleukin-1 receptor antagonist in AIDS-Kaposi's sarcoma.

Kaposi's sarcoma (KS) is the most common tumor seen in patients with HIV-1 infection. HIV-1 may induce KS directly through viral protein(s) or indirectly through regulation of cytokines such as IL-1 and IL-6. We have shown that AIDS-KS spindle cells express IL-1 beta and that IL-1ra inhibits KS-spindle cell growth. IL-1ra had little effect on human umbilical vein endothelial cells (HUVEC), human aortic smooth muscle cells (HASM), and human foreskin fibroblast (NN41). These findings support an autocrine activity for IL-1. Furthermore, exogenous IL-1 can enhance AIDS-KS cell growth, and this effect is completely blocked by IL-1ra. As expected, IL-1ra also blocks IL-1 mediated upregulation of IL-6 and bFGF, both of which are autocrine growth factors for KS. IL-1ra is thus a potential candidate for the treatment of AIDS-associated KS.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Membrane mu poly(A) signal and 3' flanking sequences function as a transcription terminator for immunoglobulin-encoding genes.

Developmentally regulated mechanisms involving alternative RNA splicing and/or polyadenylation, as well as transcription termination, are implicated in controlling the levels of secreted mu (mu s), membrane mu (mu m) and delta immunoglobulin (Ig) heavy chain mRNAs during B cell differentiation (mu gene encodes the mu heavy chain). Using expression vectors constructed with genomic DNA segments composed of the mu m polyadenylation signal region, we analyzed poly(A) site utilization and termination of transcription in stably transfected myeloma cells and in murine fibroblast L cells. We found that the gene segment containing the mu m poly(A) signals, along with 536 bp of downstream flanking sequence, acted as a transcription terminator in both myeloma cells and L cell fibroblasts. Neither a 141-bp DNA fragment (which directed efficient polyadenylation at the mu m site), nor the 536-bp flanking nucleotide sequence alone, were sufficient to obtain a similar regulation. This shows that the mu m poly(A) region plays a central role in controlling developmentally regulated transcription termination by blocking downstream delta gene expression. Because this gene segment exhibited the same RNA processing and termination activities in fibroblasts, it appears that these processes are not tissue-specific.

Alternative Splicing↗
PubMed1992

Intracellular symbionts and the evolution of uniparental cytoplasmic inheritance.

Uniparental inheritance of cytoplasmic elements is widespread among eukaryotic organisms and is achieved by a diverse range of mechanisms. This paper shows that the cytoplasmic genetic system would be expected to evolve towards uniparental inheritance, given the existence of deleterious symbionts capable of invading the host cytoplasm together with nuclear genes that lead to the elimination of cytoplasmic elements from one of the gamete types. The reason for this is that, under biparental inheritance, foreign symbionts with strong deleterious effects are able to spread through host populations. A nuclear modifier gene which leads to the loss of cytoplasmic elements from one gamete type gains a net advantage as a symbiont spreads, because the modifier sometimes gives rise to a symbiont-free zygote. Insofar as small gametes reduce the rate of symbiont transmission to the zygote, modifier genes causing small gamete size would tend to accumulate, so that cytoplasmic inheritance would become associated with maternal rather than paternal gametes. Once uniparental inheritance predominates in the host population, the population is protected from invasions by a large class of harmful symbionts, but at the same time those symbionts that benefit their hosts are still able to increase in frequency.

Animals↗
PubMed1992

Somatic cell mapping of the human cyclophilin B gene (PPIB) to chromosome 15.

The polymerase chain reaction (PCR) technique was used to generate a unique probe complementary to the hydrophobic 5' end of the human cyclophilin B gene. This unique probe was hybridized to DNAs from human x hamster hybrid somatic cell lines retaining different combinations of human chromosomes. The gene was assigned to chromosome 15.

Amino Acid Isomerases↗
PubMed1990

Lipopolysaccharide-unresponsive mutant pre-B-cell lines blocked in NF-kappa B activation.

NF-kappa B activation is a crucial late step in the induction of immunoglobulin kappa light-chain gene expression in pre-B cells by lipopolysaccharide (LPS). We have analyzed NF-kappa B activation in three independent mutant lines of 70Z/3 pre-B cells which are unresponsive to LPS. All three variant cell lines failed to activate NF-kappa B when induced with LPS or the phorbol ester 12-O-tetradecanoylphorbol 13-acetate. However, all three cell lines contained functional NF-kappa B, as revealed by detergent treatment of cytoplasmic extracts. Moreover, cycloheximide induced limited activation of NF-kappa B comparable to that in wild-type 70Z/3 pre-B cells in two of the three variant lines. These results indicate that the mutations blocking kappa gene induction in these variant 70Z/3 pre-B-cell lines affect NF-kappa B activation.

Animals↗
PubMed1989

Ethnic differences in consultation rates in urban general practice.

OBJECTIVE: To determine the patterns of consultations with the general practitioner among different ethnic groups and the outcome of these consultations. DESIGN: Retrospective analysis of data from one urban group general practice collected during 1979-81 as part of a research project in seven practices. SETTING: Group general practice in the London borough of Brent with a list size of 10,877 patients in July 1980. SUBJECTS: Patients registered with the practice during the 23 months to April 1981 who accounted for 67,197 consultations. MAIN OUTCOME MEASURES: Ethnic state, sex and social class distribution, and diagnosis of patients consulting and frequency of consultations analysed as standardised consultation ratios and standardised patient consultation ratios. RESULTS: Compared with other ethnic groups male Asians (that is, including those born in Britain and those originating from the Indian subcontinent and east Africa) had a substantially increased standardised patient consultation ratio. Consultation rates for mental disorders--in particular, anxiety and depression--were reduced in all groups of immigrant descent. West Indians consulted more frequently for hypertension and asthma, and their children less frequently with otitis media. Asians consulted more frequently with upper respiratory tract infections and non-specific symptoms. Native British patients were more likely to leave the surgery with a follow up appointment, prescription, or certificate. CONCLUSION: Notwithstanding the limitations of this study, ethnic differences in consultation rates were apparent. These differences require further investigation if the needs of minority ethnic groups are not to be overlooked.

Asia↗
PubMed1989

Impact of a recapping device on venepuncture-related needlestick injury.

In a 33-month prospective analysis of needlestick injuries, venepuncturists working under Centers for Disease Control (CDC) guidelines for handling used needles were shown to incur a needlestick injury for every 3,175 to 4,006 needle-handling procedures. On the other hand, users of a simple device designed to reduce the risk of injury when recapping used needles were shown to incur a needlestick only once in every 16,100 venepunctures performed (P less than 0.001). This represents a fourfold reduction in the rate of needlestick injuries. We thus question the effectiveness of the CDC nonrecapping policy.

Accidents, Occupational↗
PubMed1988

Sequence-dependent variability of DNA structure. Influence of flanking sequences and fragment length on digestion by conformationally sensitive nucleases.

DNase I and 1,10-phenanthroline-copper are two nucleolytic activities which are sequence-dependent in their scission reaction yet are not nucleotide-specific at their site of cutting. When these two nucleases are used to digest identical sequences in 18-base pair oligonucleotides and in restriction fragments 10-fold longer, the digestion patterns are similar at sequence positions in the interior of the fragment. Changes in reactivity to 1,10-phenanthroline-copper associated with mutational changes in the lac promoter in biochemically functional restriction fragments are duplicated in 18-base pair oligonucleotides. The structural variability of a given DNA sequence detected by these conformationally sensitive nucleolytic activities is therefore encoded in local sequence and not sensitive to fragment length. Digestion patterns of a repeated 7-base pair sequence within a longer sequence have the same characteristic except for the two nucleotides at the 5' periphery of the direct repeat. This conclusion is based on the digestion pattern of a restriction fragment which contains the polyadenylation site of the mouse immunoglobulin mu heavy chain gene. Two pairs of different 7-base pair sequences repeated in this fragment retain their distinctive digestion patterns. DNA sequences which comprise the binding sites of regulatory proteins, retain a characteristic structure only influenced at their peripheries by two to three bases of the flanking sequence.

DNA↗
PubMed1987

Conditions for the initial increase of new alleles with frequency dependent selection.

The paper presents the derivation of conditions for the initial increase of a new allele in a fairly general model of a one locus genetic system. Incorporated within the model are frequency dependent selection coefficients which allow the study of viability differences, fertility differences, segregation distortion and certain forms of non-random mating. Since in many models it is necessary to go beyond linear terms, quadratic, cubic and quartic terms are also derived explicitly and details given of their extension to higher degrees.

Alleles↗
PubMed1987

Protein-binding site at the immunoglobulin mu membrane polyadenylylation signal: possible role in transcription termination.

mRNAs specifying immunoglobulin mu and delta heavy chains are encoded by a single large, complex transcription unit (mu + delta gene). The transcriptional activity of delta gene segments in terminally differentiated, IgM-secreting B lymphocytes is 10-20 times lower than in earlier B-lineage cells expressing delta mRNA. We find that transcription of the mu + delta gene in IgM-secreting murine myeloma cells terminates within a region of 500-1000 nucleotides immediately following the mu membrane (mu m) polyadenylylation site. Transcription decreases only minimally through this region in murine cell lines representative of earlier stages in B-cell development. A DNA fragment containing the mu m polyadenylylation signal gives protein-DNA complexes with different mobilities in gel retardation assays with nuclear extracts from myeloma cells than with nuclear extracts from earlier B-lineage cells. However, using a recently developed "footprinting" procedure in which protein-DNA complexes resolved in gel retardation assays are subjected to nucleolytic cleavage while still in the polyacrylamide gel, we find that the DNA sequences protected by factors from the two cell types are indistinguishable. The factor-binding site on the DNA is located 5' of the mu m polyadenylylation signal AATAAA and includes the 15-nucleotide-long A + T-rich palindrome CTGTAAACAAATGTC. This type of palindromic binding site exhibits orientation-dependent activity consistent with the reported properties of polymerase II termination signals. This binding site is followed by two sets of directly repeated DNA sequences with different helical conformation as revealed by their reactivity with the chemical nuclease 1,10-phenanthroline-copper. The close proximity of these features to the signals for mu m mRNA processing may reflect a linkage of the processes of developmentally regulated mu m polyadenylylation and transcription termination.

B-Lymphocytes↗
PubMed1985

Permanent coexistence in general models of three interacting species.

We address the question of the long term coexistence of three interacting species whose dynamics are governed by the ordinary differential equations xi = xifi(i = 1,2,3). In order for any theory in this area to be useful in practice, it must utilize as little information as possible concerning the forms of the fi, in view of the great difficulty of determining these experimentally. Here we obtain, under rather general conditions on the equations, a criterion for judging whether the species will coexist in a biologically realistic manner. This criterion depends only on the behaviour near the one or two species equilibria of the two dimensional subsystems, the behaviour there being relatively easy to examine experimentally. We show that with the exception of one class of cases, which is a generalization of a classical example of May and Leonard [21], invasibility at each such equilibrium suitably interpreted is both necessary and sufficient for a strong form of coexistence to hold. In the exceptional case, a single additional condition at the equilibria is enough to ensure coexistence.

Animals↗
PubMed1980

The ages of man.

A new approach to continuing education for the experienced general practitioner is described which makes use of small group work, provides a longitudinal framework for planning over several years, and by its flexibility permits the participants to shape the content to their needs. The principles behind the approach are described and each year's work considered with a discussion of the problems that emerged, what the attenders and organizers learned, and how the series evolved.

Curriculum↗
PubMed1976

Medicines and elderly people: a general practice survey.

All 151 patients of 75 years and over in one practice were visited at home to survey their health and how they managed their medicines. Altogehter 87% were on regular treatment, 34% taking three or four different drugs each day. Most were responsible for their own drugs and managed them well, but many left their drugs in exposed places and were uncertain about how to dispose of unwanted medicines. Overall they were prescribed about three times the number of drugs prescribed for the general population, and women took twice as many drugs regularly as men. Although many drugs were obtained directly from a pharmacist, his advice was rarely sought. Most were labelled, but more explicit instructions about indications for taking the drug would have been helpful, and information about hoarded drugs would have been enhanced by dispensing and expiry dates. Treatment was facilitated when patients brought their drugs to the consultation and careful records were made of repeat prescriptions. As so many patients take three or more different types of drugs each day a container in which a day's supply could be laid out would be useful.

Aged↗
PubMed1976

The continuing challenge of acute and perforated appendicitis.

A two year review of 216 patients with a preoperative diagnosis of appendicitis is used to help clarify the continuing points of controversy concerning appendicitis. Morbidity of perforated appendicitis by far exceeds that of nonperforated cases. Twenty-nine per cent of patients had perforation with a postoperative complication rate of 33 per cent. Rate of wound infection after perforation was 15 per cent despite antibiotics and delayed wound closure. Pediatric patients in this study did not experience a higher incidence of perforation or complication. A decision tree for management of acute appendicitis is presented.

Abscess↗