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Biomedical subjects

J Cooke

Publications and source records attributed to J Cooke.

At least 37 records · Page 2Linked to original sources
PubMed1999

Flik, a chick follistatin-related gene, functions in gastrular dorsalisation/neural induction and in subsequent maintenance of midline Sonic hedgehog signalling.

We have targetted the chick gene Flik with antisense oligodeoxynucleotide treatment at gastrular stages, when it is expressed in organiser-derived structures of the midline (K. Patel et al., 1996, Dev. Biol. 178, 327-342). A specific syndrome of deficient axial patterning and holoprosencephaly is produced. Most aspects of this syndrome can be understood as due to attenuation of dorsalising and neural-inducing signals during gastrulation, followed by failure to maintain the later signals from chordamesoderm/neural midline that pattern the mesodermal and neural cross sections during subsequent stages. Anatomical effects are first apparent at early neurula stages and correspond with what might be expected from a reduced counteraction of the ventralising Bone morphogenetic protein (BMP) pathway at the earlier stages, coupled with inadequate Sonic hedgehog (Shh) signalling subsequently. Delay in the clearing of BMP-4 RNA expression from the presumptive neural region at gastrulation is indeed seen, though chordin RNA expression within organiser derivatives remains normal. Subsequently, specific attenuation of chordamesoderm and neural midline Shh expression is observed. Brief preincubation of stage 4 chick blastoderms in supernatant from Xenopus oocytes that have been injected with Flik RNA prolongs and enhances the competence of their peripheral epiblast to respond to neural inductive signals from grafted Hensen's nodes. This effect specifically mimics that recently observed using microg/ml solutions of recombinant Follistatin (D. J. Connolly et al., 1999, Int. J. Dev. Biol., in press), further suggesting that Flik protein might act in vivo by somehow modulating activity of signalling pathways through BMP or other TGFbeta-related ligands. We discuss the significance of the observations in relation to recent ideas about neural induction, about possible redundancy in gene action, and about subsequent patterning of the axial cross section, suggesting that a Flik function in autocrine/paracrine maintenance of later midline Shh signalling represents a role of the gene separate from that in primary dorsalisation/neural induction.

Amino Acid Sequence↗
PubMed1999

Nodal signalling and the roles of the transcription factors SnR and Pitx2 in vertebrate left-right asymmetry.

Left-specific mesodermal expression of the homeobox gene Pitx2 links a gastrula-stage intercellular signalling cascade to the later development of vertebrate left-right organ asymmetry through the Nodal signalling pathway [1] [2][3] [4][5] [6]. SnR (Drosophila snail-related), a gene conserved in vertebrates and encoding a zinc-finger protein, appears to function in a similar manner to Pitx2, but through right-specific mesodermal expression [7] [8]. Here, we present direct evidence for an earlier proposal [7] that Nodal signalling specifically represses expression of SnR in left lateral mesoderm, and thus ensures its normal confinement to the right, while activating Pitx2 on the left. We addressed the relationship between Pitx2 and SnR using antisense disruption of SnR. Relatively severe antisense-SnR treatment led to massive ectopic expression of Pitx2 on the right, accompanied by randomisation of situs with embryos showing aspects of left-cardiac isomerism. This indicates a gene cascade relationship in the propagation of left-right information, whereby nodal activates Pitx2 on the left through a double-negative mechanism involving the repression of SnR's repressor role on Pitx2. Milder antisense-SnR treatment reversed heart-loop direction and embryo torsion at significant incidence, although Pitx2 expression remained normally left-confined throughout. This reversed morphology following SnR disruption alone appeared different from that in which additional ectopic right-hand Pitx2 expression was seen. Therefore, in addition to their regulatory gene cascade relationship, these two transcription factors appear to have further, parallel but non-redundant, roles in directly controlling normally right- and left-specific morphogenetic processes.

Animals↗
PubMed1999

The significance of spontaneous resolution of breast calcification.

Spontaneously resolving breast microcalcification is a rarely reported occurrence. A retrospective review was carried out on 33 cases of resolving benign and indeterminate microcalcification identified from 108,000 screening mammograms from the South West London Breast Screening Service. Four further cases are reported from The Jarvis Breast Screening Centre. No interval cancers were identified in women with microcalcification which initially showed benign appearances. However, 36.4% of the group with resolving indeterminate microcalcification subsequently developed cancers. It is recommended that this change should prompt full investigation and close follow-up or excision. While the majority of spontaneously resolving microcalcification is associated with benign processes, it is concluded that a significant proportion of disappearing indeterminate microcalcification is associated with malignancy.

Aged↗
PubMed1999

Analysis of optical density and contrast in mammograms.

The objective of this project is the development of tools for the UK NHSBSP to assess image quality quantitatively in clinical films, for the purposes of optimizing imaging procedures and audit. As an initial step, 120 mammograms of 46 women on a single day of screening were digitized and analysed to produce indices of optical density (OD) and contrast. Analysis was performed on three regions of interest (ROI): pectoral muscle, main breast and skin edge. Two radiologists independently graded the quality of information in the different parts of each mammogram, and categorized breast type as either "dense", "mixed density" or "fatty". Measurements of contrast and OD generally correlated well with the opinions of the radiologists. For the oblique mammograms, the mean OD in the main breast ranged between films from 1.25 to 2.24 with a mean of 1.69 +/- 0.02. In the craniocaudal mammograms, the mean OD in the main breast ROI ranged from 1.14 to 1.94 with a mean of 1.61 +/- 0.05. The OD for a quality control film of a 40 mm block of PMMA exposed on the same day with this system was 1.53. A contrast index (CI) was calculated for each mammogram as the difference between the points of maximum and minimum OD in the main breast. Mean CI was 1.02 +/- 0.09 for fatty breasts, 1.50 +/- 0.10 for mixed density breasts and 2.05 +/- 0.23 for dense breasts. A review of the radiologist assessments indicated that the main breast was satisfactorily displayed when glandular and fatty tissues were displayed within the OD range 0.8-2.9. An analysis of the dynamic range requirements showed that 17% of films had a dynamic range that lay above that calculated using the suggested OD limits.

Breast Neoplasms↗
PubMed1999

Secretory immunoglobulin A and cardiovascular activity during mental arithmetic and paced breathing.

The role of the autonomic nervous system in secretory immunoglobulin A (sIgA) responses to laboratory challenge was explored in a study in which sIgA and cardiovascular activity were recorded at rest and during mental arithmetic and paced breathing. These tasks were selected to preferentially engage the sympathetic and parasympathetic nervous systems, respectively. Mental arithmetic elicited a mixed pattern of increased alpha- and beta-adrenergic activity and a reduction in parasympathetic activity; diastolic blood pressure, total peripheral resistance, and systolic blood pressure increased, preejection period shortened, and heart rate variability decreased. In contrast, paced breathing primarily elicited an increase in parasympathetic activity; heart rate variability increased. Mental arithmetic also provoked an increase in sIgA concentration but no change in saliva volume, whereas paced breathing affected neither sIgA concentration nor saliva volume. These data suggest that sIgA responses to laboratory challenges are mediated by sympathetic rather than parasympathetic processes.

Adult↗
PubMed1998

Eph signaling is required for segmentation and differentiation of the somites.

Somitogenesis involves the segmentation of the paraxial mesoderm into units along the anteroposterior axis. Here we show a role for Eph and ephrin signaling in the patterning of presomitic mesoderm and formation of the somites. Ephrin-A-L1 and ephrin-B2 are expressed in an iterative manner in the developing somites and presomitic mesoderm, as is the Eph receptor EphA4. We have examined the role of these proteins by injection of RNA, encoding dominant negative forms of Eph receptors and ephrins. Interruption of Eph signaling leads to abnormal somite boundary formation and reduced or disturbed myoD expression in the myotome. Disruption of Eph family signaling delays the normal down-regulation of her1 and Delta D expression in the anterior presomitic mesoderm and disrupts myogenic differentiation. We suggest that Eph signaling has a key role in the translation of the patterning of presomitic mesoderm into somites.

Amino Acid Sequence↗
PubMed1998

Cost issues in sequential therapy.

Pharmacoeconomics is starting to be employed in strategic therapeutic decision making. Costs associated with antimicrobials included: (i) acquisition costs; (ii) preparation, administration and consumables costs; (iii) monitoring costs; (iv) costs of unwanted drug effects; (v) costs of resistance and therapeutic failures and (vi) costs of duration of stay. Most hospitals have a Drug and Therapeutics Committee but acquisition costs are still the most important economic criterion for acceptance for use, even though medicines only consume between 3 and 5% of total revenue costs, of which antibiotics account for around 15%. In any sequential programme acquisition costs and consumables are immediately realizable. Staff time and monitoring tests are less realizable but require changes in the way budgets are handled. Microbial resistance and risk management are difficult to quantify but are increasingly becoming important in strategic decision-making. The educational needs of health care decision makers in economic need addressing and mechanisms need to be put in place to enable the putative savings reported in the pharmacoeconomic literature to be realized.

Administration, Oral↗
PubMed1998

A cascade of gene action controlling heart asymmetry and torsion in embryonic development.

Lateralized looping of the heart tube, with associated torsion of the embryo axis, is the first structural sign of the consistent left-right asymmetrical organization that characterizes all vertebrate embryos. Rare failures or reversals of this asymmetry in humans lead to clinically important syndromes of malformation in heart and great blood vessels. Recently, elements of the genetic control sequence underlying this left-right aspect of development have been uncovered. The normal sequence of transmission for asymmetry information can now be traced to a point close to the actual execution of right-hand looping in the heart tube, with the hope that the further sequence of gene activity, within the heart itself and directing these events, may soon be uncovered.

Journal Article↗
PubMed1997

Left/right patterning signals and the independent regulation of different aspects of situs in the chick embryo.

Recently, a pathway of genes which are part of a cascade regulating the side on which the heart forms during chick development was characterized (M. Levin et al., 1995, Cell 82, 1-20). Here we extend these previous studies, showing that manipulation of at least one member of the cascade, Sonic hedgehog (Shh), can affect the situs of embryonic rotation and of the gut, in addition to the heart. Bilateral expression of Shh, which is normally found exclusively on the left, does not result in left isomerism (a bilaterally symmetrical embryo having two left sides) nor in a complete situs inversus phenotype. Instead, misexpression of Shh on the right side of the node, which in turn leads to bilateral nodal expression, produces a heterotaxia-like condition, where different aspects of laterality are determined independently. Heart situs has previously been shown to be altered by ectopic Shh and activin. However, the most downstream gene identified in the LR pathway, nodal, had not been functionally linked to heart laterality. We show that ectopic (right-sided) nodal expression is able to affect heart situs, suggesting that the randomization of heart laterality observed in Shh and activin misexpression experiments is a result of changes in nodal expression and that nodal is likely to regulate heart situs endogenously. The first defined asymmetric signal in the left-right patterning pathway is Shh, which is initially expressed throughout Hensen's node but becomes restricted to the left side at stage 4(+). It has been hypothesized that the restriction of Shh expression may be due to repression by an upstream activin-like factor. The involvement of such an activin-like factor on the right side of Hensen's node was suggested because ectopic activin protein is able to repress Shh on the left side of the node, as well as to induce ectopic expression of a normally right-sided marker, the activin receptor cAct-RIIa. Here we provide further evidence in favor of this model. We find that a member of this family, Activin betaB, is indeed expressed asymmetrically, only on the right side of Hensen's node, at the correct time for it to be the endogenous asymmetric activin signal. Furthermore, we show that application of follistatin-loaded beads eliminates the asymmetry in Shh expression, consistent with an inhibition of an endogenous member of the activin-BMP superfamily. This combined with the previous data on exogenous activin supports the model that Activin betaB functions in the chick embryo to initiate Shh asymmetry. While these data extend our understanding of the early signals which establish left-right asymmetry, they leave unanswered the interesting question of how the bilateral symmetry of the embryo is initially broken to define a consistent left-right axis. Analysis of spontaneous chick twins suggests that, whatever the molecular mechanism, left-right patterning is unlikely to be due to a blastodermal prepattern but rather is initiated in a streak-autonomous manner.

Animals↗
PubMed1997

Evolution of genetic redundancy.

Genetic redundancy means that two or more genes are performing the same function and that inactivation of one of these genes has little or no effect on the biological phenotype. Redundancy seems to be widespread in genomes of higher organisms. Examples of apparently redundant genes come from numerous studies of developmental biology, immunology, neurobiology and the cell cycle. Yet there is a problem: genes encoding functional proteins must be under selection pressure. If a gene was truly redundant then it would not be protected against the accumulation of deleterious mutations. A widespread view is therefore that such redundancy cannot be evolutionarily stable. Here we develop a simple genetic model to analyse selection pressures acting on redundant genes. We present four cases that can explain why genetic redundancy is common. In three cases, redundancy is even evolutionarily stable. Our theory provides a framework for exploring the evolution of genetic organization.

Animals↗
PubMed1997

Control of vertebrate left-right asymmetry by a snail-related zinc finger gene.

A gene encoding a zinc finger protein of the Snail family, cSnR, is expressed in the right-hand lateral mesoderm during normal chick development. Antisense disruption of cSnR function during the hours immediately preceding heart formation randomized the normally reliable direction of heart looping and subsequent embryo torsion. Implanted ectopic sources of intercellular signal proteins that are involved in establishing normal left-right information randomized the handedness of heart development and also altered the asymmetry of cSnR expression. cSnR thus appears to act downstream of these signals, or perhaps in parallel with the latest expressed of them, the Nodal protein, in controlling the anatomical asymmetry.

Activin Receptors↗
PubMed1997

Immune complexes bound to the primate erythrocyte complement receptor (CR1) via anti-CR1 mAbs are cleared simultaneously with loss of CR1 in a concerted reaction in a rhesus monkey model.

In the circulation of primates, C3b-opsonized immune complexes (IC) bound to erythrocyte (E) CR1 are taken to the liver and spleen where IC are removed and destroyed without lysis or sequestration of E. Individuals with diseases associated with IC processing often have decreased E CR1 levels, and in previous primate animal models of IC disease, E CR1 was shown to be reduced, but the relationship between IC processing and CR1 loss remained to be clarified. We have developed a simple model to study this question. In naive (nonimmunized) rhesus monkeys, E-bound mouse anti-CR1 mAbs (1500 IgG/E) are not rapidly cleared from the circulation. Infusion of monkey anti-mouse IgG leads to rapid indirect binding of this second antibody to E CR1. Subsequently, in what appears to be a concerted reaction, CR1-bound nascent IC are rapidly cleared from the circulation and CR1 is removed from E at the same rate. Clearance of bound IC and loss of CR1 were both independently followed by RIA. Imaging studies localized the cleared anti-CR1 mAbs to the liver. Western blots indicated that the loss of CR1 was not due to a conformational change, and E CR1 levels returned to normal in 2-3 weeks, suggesting that the return was associated with synthesis of new E. Our findings suggest that the key step in the clearance mechanism requires recognition (possibly by Fc receptors) of IC-like material associated with E CR1, and this leads to loss of CR1 and uptake of the CR1-IC substrate by liver phagocytic cells.

Animals↗
PubMed1997

Economic evaluations of drug therapy: attitudes of primary care prescribing advisers in Great Britain.

All health authorities in Great Britain have both medically or pharmaceutical qualified staff to advise both the authority and the local primary care medical practitioners about drug use and prescribing. This study used a piloted postal questionnaire to assess the attitudes of these advisers to economic evaluations of drug therapy, and their perceptions of the barriers to achieving cost effective prescribing by use of these evaluations. There was a 65% response rate to the questionnaire. Economic issues were rated by advisers to be less important than clinical issues, but were considered at most meetings between advisers and primary care medical practitioners. Advisers wished to consider true cost effective prescribing but often felt obliged to consider drug acquisition costs and risks of budgetary overspends. The perceived inflexibility of existing structures within the British National Health Service and the lack of credibility of the evaluations (often perceived as pharmaceutical industry marketing) were the major barriers to the application of the evaluations. The paper concludes that advisers were keen to use economic evaluations to promote cost effective prescribing but were impeded by the perceived bias of existing studies and by rigid current NHS structures.

Attitude of Health Personnel↗