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Biomedical subjects

M Stewart

Publications and source records attributed to M Stewart.

At least 325 records · Page 18Linked to original sources
PubMed1990

Expression and characterization of human lamin C.

We have expressed human lamin C cDNA in E. coli using a modification of the pLcII vector system. Protein produced in this way had seven additional amino acids at its N-terminus, but retained key lamin structural and assembly properties. The modified vector we produced may prove useful when difficulties are encountered in removal of the cII fusion peptide by factor X cleavage in the pLcII system. Shadowed preparations of expressed lamin C showed the presence of 50-nm rod-like particles that closely resembled those observed for native material. Isolated molecules had two globular domains at one end, indicating that they were constructed from two parallel polypeptide chains. The expressed material also formed paracrystals with a characteristic 22.5 nm axial repeat, indicating that its assembly properties had also been retained. We also used site-specific mutagenesis to engineer a lamin fragment that lacked the C-terminal non-helical domain of the molecule. This material formed paracrystals similar to those obtained with the intact molecule, indicating that the large C-terminal non-helical domain did not contain information vital for lamin assembly.

Cloning, Molecular↗
PubMed1990

Association of gold-labelled nucleoplasmin with the centres of ring components of Xenopus oocyte nuclear pore complexes.

We have used heavy-metal shadowing to study the interaction of morphological components of Xenopus oocyte nuclear pore complexes with nucleoplasmin conjugated to colloidal gold. When microinjected into Xenopus oocytes, gold-labelled nucleoplasmin accumulated on the axis of the pores. Envelopes partially disrupted by treatment with low ionic strength buffer produced isolated islands of pores together with substantial quantities of rings deriving from the cytoplasmic and nucleoplasmic faces of the pores. In preparations from oocytes in which nucleoplasmin-gold had been microinjected, most (238/288) of the rings examined had also been labelled and, in the majority of these (60%), the label was located centrally within isolated rings. The central positioning of the nucleoplasmin-gold in isolated rings indicated that these morphological components of the pores were probably involved in the transport of nucleoplasmin into the nucleus, either by way of the initial binding of the molecule or by way of its translocation across the nuclear envelope. Although more work is required to resolve the precise stage at which the rings are involved, a number of lines of evidence suggested that they were more likely to be involved in the translocation step rather than in initial binding of nucleoplasmin.

Animals↗
PubMed1990

Structural predictions for the central domain of dystrophin.

The amino acid sequence of dystrophin indicates that the molecule has globular N- and C-terminal domains separated by a long central rod domain. The central rod contains multiple repeats, about 100 amino acids long and of variable length. These diverge sufficiently in sequence that, in previous studies, only 14 of the most similar repeats have been aligned and analysed in any detail. We show here that a heptad pattern of hydrophobic residues is preserved across all repeats. Using the heptad pattern together with a consensus sequence template, we identified and aligned 25 repeats in the dystrophin rod sequence. Each repeat consists of a constant-length core helix of 54 residues, coupled via a short linker to a weakly conserved variable-length helix, and then via a second linker to the next core. The variable-length helix appears truncated in repeats 10 and 13 and extended in repeats 4 and 20. The extension of repeat 20 is particularly interesting since it corresponds to a hotspot of dystrophy-inducing mutations. Detailed modelling suggests that the classical Speicher-Marchesi [(1984) Nature 311, 177-180] model for spectrin may not be appropriate to dystrophin without some modification. We propose that whilst the repeating structural motif in dystrophin is probably a bead of triple coiled coil, this bead is twice as massive as, and out of phase with, those proposed for spectrin. Our model raises the possibility that the rod domain of dystrophin may confer elasticity on the molecule. Deletions which truncate this region would then reduce the extensibility of the molecule without affecting actin crosslinking, consistent with their typically producing the relatively benign Becker phenotype of muscular dystrophy.

Actinin↗
PubMed1990

Corticospinal responses to electrical stimulation of motor cortex in the rat.

Direct and indirect corticospinal responses to electrical stimulation of motor cortex were identified in urethane-anesthetized rats. 'Killed-end' recordings were taken from the corticospinal tract at the level of the cervical cord (C1-C2) and from the medullary pyramid. The identities of direct (D) and indirect (I) corticospinal responses were confirmed by: (1) removing motor cortex to eliminate I activity, and (2) pharmacologically increasing neocortical excitability, prior to any lesions, to increase I activity. Our data indicate that the conduction velocity of the fastest corticospinal fibers is approximately 18 m/s. Our identification of the components of the corticospinal response will permit the interpretation of the more complicated surface or 'non-killed-end' depth recordings which have shown particular utility in evaluating spinal cord damage.

Action Potentials↗
PubMed1990

Firing relations of lateral septal neurons to the hippocampal theta rhythm in urethane anesthetized rats.

The firing of lateral septal neurons was examined in relation to the hippocampal theta rhythm in urethane anesthetized rats. In general, the firing rates of these cells were low during both theta and non-theta EEG states. There was no significant change in firing rate between the two states (theta: 8.5 +/- 9.9 spks/sec; non-theta: 6.0 +/- 5.3). Sixty-four of 68 cells fired simple spikes and 4 cells were found to fire bursts of action potentials (complex-spikes). Approximately 30% (21/65) of the cells showed a significant phase relation to the hippocampal theta rhythm. The preferred phases of firing of these 21 cells were broadly distributed. The possibility that the phase-locked firing of LSN cells is due to the phase-locked firing of hippocampal projection cells is discussed.

Action Potentials↗
PubMed1990

Mothers' views on the ages of onset for four childhood disorders.

The mothers of 120 consecutive children in our outpatient clinic were asked a series of questions about their views on the ages at which their children became deviant. The symptoms of autism were the earliest noted at 15 months. Those with symptoms of attention-deficit hyperactivity disorder (ADHD), or conduct disorder plus ADHD, did not separate by age of onset. The mean for both groups was the fourth year of life. Children with conduct disorder alone had a putative age of onset of six years.

Attention Deficit Disorder with Hyperactivity↗
PubMed1990

Preoperative radiotherapy followed by radical vulvectomy with inguinal lymphadenectomy for advanced vulvar carcinomas.

A therapeutic alternative to exenteration for large locally advanced vulvar carcinoma involving the rectum, anus, or vagina is the use of preoperative radiation followed by radical surgery. Between 1980 and 1988, 13 patients with Stage III and 3 with Stage IV vulvar carcinoma involving the rectum/anus, urethra, or vagina were treated with 4000 rad to the vulva and 4500 rad to the inguinal and pelvic nodes followed by a radical vulvectomy and inguinal lymphadenectomy 4 weeks later. The overall 5 year cumulative survival was 45%. Twelve tumors regressed after radiation with 62.5% of the patients having visceral preservation while in 4 patients there was no major response to radiation and urinary or fecal diversion was required. Of the 6 recurrences 4 were central and 2 distant. Three patients with central recurrences had tumor within 1 cm of the vulvectomy margin. Complications included wet desquamation, inguinal wound separation, lymphedema, and urethral strictures. There were no operative deaths. It is concluded that the use of preoperative radiation followed by radical vulvectomy may be an alternative to pelvic exenteration in selected patients with advanced vulvar lesions.

Adult↗
PubMed1990

Do septal neurons pace the hippocampal theta rhythm?

The hippocampal theta rhythm (rhythmical slow activity, RSA) is one of the most thoroughly studied EEG phenomena. Much of this experimental interest has been stimulated by suggestions that the mnemonic functions of the hippocampus may depend upon theta-related neuronal activity. Inputs from the medial septal nuclei to the hippocampus were shown to be essential for the theta rhythm in the 1950s, but the role of these basal forebrain projections has not been clearly defined. Four models of the septo-hippocampal connections involved in theta rhythm production are reviewed as the precise roles of these projections are discussed. In our final, consolidated model both cholinergic and GABAergic septal projection cells fire in rhythmic bursts that entrain hippocampal interneurons. The resulting rhythmic inhibition of hippocampal projection cells, together with their excitatory interconnections, generates at least one component of the theta rhythm.

Action Potentials↗
PubMed1990

Surgical rescue for failures of cirrhotic sclerotherapy.

Bleeding from gastroesophageal varices remains the most devastating complication of the portal hypertensive syndrome. Endoscopic sclerotherapy has emerged as the best initial treatment for bleeding varices because surgery is obviated and survival may be improved. However, sclerotherapy will fail and surgical rescue will be required in at least a third of patients. There are two viable surgical rescue procedures: shunt surgery and liver transplantation. This paper summarizes the available data and concludes that there is a role for both procedures.

Esophageal and Gastric Varices↗
PubMed1990

Comparison of a human granular cell tumour (myoblastoma) with granular cell tumours (meningiomas) of the rat meninges--an immunohistological and ultrastructural study.

A single human granular cell tumour (myoblastoma) was compared with seven rat granular cell tumours (meningiomas) of the meninges. The comparison was made histologically, ultrastructurally and using immunocytochemical markers. A selection of antibodies to histiocytic, muscle, neural, neural crest and mesenchymal antigens was used. Histogenesis of both the human and rat tumours from neural crest-derived cells was evident and it is suggested that the term 'meningioma' for these rat tumours is a misnomer.

Animals↗
PubMed1990

Oestrogen and progesterone receptors in carcinoma of the cervix.

Oestrogen (ER) and progesterone (PR) receptors have been measured in 102 cervical carcinomas. With positive levels defined as concentrations exceeding 20 fmol/mg protein for cytoplasmic receptor and/or 200 fmol/mg DNA for nuclear receptor, 24% of tumours were dual receptor positive and 51% were dual receptor negative. The majority of adenocarcinomas (81%: 13/16) expressed ER (P less than 0.001) though only 54% (7/13) of these tumours co-expressed PR. There was a significant correlation between tumours positive for ER and those arising in premenopausal women (P = 0.011), with good or moderate differentiation (P = 0.027) and of smaller size (P = 0.025). Median follow-up is 19 months. Apart from advanced stage, tumour bulk (greater than 5 cm) was the only parameter associated with inferior progression-free survival, and most larger tumours were of advanced stage. No prognostic significance could be detected for receptor status.

Adenocarcinoma↗
PubMed1990

Complete sequence of the Drosophila nonmuscle myosin heavy-chain transcript: conserved sequences in the myosin tail and differential splicing in the 5' untranslated sequence.

We have sequenced a cDNA that encodes the nonmuscle myosin heavy chain from Drosophila melanogaster. An alternatively spliced exon at the 5' end generates two distinct heavy-chain transcripts: the longer transcripts inserts an additional start codon upstream of the primary translation start site and encodes a myosin heavy chain with a 45-residue extension at its amino terminus. The remainder of the coding sequence reveals extensive homology with other conventional myosins, especially metazoan nonmuscle and smooth muscle myosin isoforms. Comparisons among available myosin heavy-chain sequences establish that characteristic differences in sequence throughout the length of both the globular myosin head and extended rod-like tail readily distinguish nonmuscle and smooth muscle myosins from striated muscle isoforms and predict a basis for their functional diversity.

Amino Acid Sequence↗
PubMed1990

Human endothelial actin-binding protein (ABP-280, nonmuscle filamin): a molecular leaf spring.

Actin-binding protein (ABP-280, nonmuscle filamin) is a ubiquitous dimeric actin cross-linking phosphoprotein of peripheral cytoplasm, where it promotes orthogonal branching of actin filaments and links actin filaments to membrane glycoproteins. The complete nucleotide sequence of human endothelial cell ABP cDNA predicts a polypeptide subunit chain of 2,647 amino acids, corresponding to 280 kD, also the mass derived from physical measurements of the native protein. The actin-binding domain is near the amino-terminus of the subunit where the amino acid sequence is similar to other actin filament binding proteins, including alpha-actinin, beta-spectrin, dystrophin, and Dictyostelium abp-120. The remaining 90% of the sequence comprises 24 repeats, each approximately 96 residues long, predicted to have stretches of beta-sheet secondary structure interspersed with turns. The first 15 repeats may have substantial intrachain hydrophobic interactions and overlap in a staggered fashion to yield a backbone with mechanical resilience. Sequence insertions immediately before repeats 16 and 24 predict two hinges in the molecule near points where rotary-shadowed molecules appear to swivel in electron micrographs. Both putative hinge regions are susceptible to cleavage by proteases and the second also contains the site that binds the platelet glycoprotein Ib/IX complex. Phosphorylation consensus sequences are also located in the hinges or near them. Degeneracy within every even-numbered repeat between 16 and 24 and the insertion before repeat 24 may convert interactions within chains to interactions between chains to account for dimer formation within a domain of 7 kD at the carboxy-terminus. The structure of ABP dimers resembles a leaf spring. Interchain interactions hold the leaves firmly together at one end, whereas intrachain hydrophobic bonds reinforce the arms of the spring where the leaves diverge, making it sufficiently stiff to promote high-angle branching of actin filaments. The large size of the leaves, their interruption by two hinges and flexible actin-binding site, facilitate cross-linking of widely dispersed actin filaments.

Amino Acid Sequence↗
PubMed1990

Patient-centredness in the consultation. 2: Does it really make a difference?

The major purpose of this study was to test the hypothesis that patient-centredness in the consultation was associated with improved patient outcomes. Patient-centred care was defined as care in which the doctor responded to the patient in such a way as to allow the patient to express all of his or her reasons for coming, including: symptoms, thoughts, feelings and expectations. The study took place in the offices of six family doctors. All consultations were audiotaped and the patients completed a questionnaire and two structured interviews with the investigator: one immediately following the consultation and the other two weeks later. Patient-centredness was found to be associated with the doctor having ascertained the patient's reasons for coming and with resolution of the patient's concerns. It was also associated with the patient feeling understood and resolution of the patient's symptoms until confounding variables were controlled. The results of the multivariate analysis suggested that the impact of a patient-centred approach may be part of a package of care, consisting of a doctor whose overall practice allows for the development of personal relationships with patients over time through continuity of care.

Communication↗
PubMed1990

Malignant melanoma in England: risks associated with naevi, freckles, social class, hair colour, and sunburn.

In a case-control study in the Midlands of England, 195 subjects with superficial spreading or nodular melanoma were compared to age- and sex-matched controls chosen from all inpatients or outpatients in hospitals serving the defined source population. Significant increases in melanoma risk, after adjustment for other factors, were seen in association with total naevi on the arms (odds ratio (OR), for 15+ naevi compared to none = 3.8), intense freckling as an adult (OR = 6.2), and as a child (OR = 6.0), and higher social class (OR = 2.4). Positive single factor associations were also seen with light or red hair colour, tendency to sunburn easily, and a history of sunburn at ages 8-12, although these were not significant when adjusted for the other factors. No significant effect was seen with naevi greater than 6 mm, or with raised naevi, when adjusted for total number of naevi. Total arm naevi and density of freckling had independent effects, consistent with a multiplicative effect, the OR in those with 10+ naevi and heavy freckling being 20.8. The risk associated with red hair was independent of naevi, but associated with freckling. The strongest association with sunburn history was seen with a history of sunburn in childhood, with sunburn at later times, having smaller effects, or none. These results shows that freckling and social class as well as naevi are strong and independent risk indicators for melanoma. These associations were generally consistent by type of melanoma, sex, age, and extent of regular exposure of the body site affected, although the social class gradient was observed neither for nodular melanoma nor for melanomas occurring on the most exposed body sites.

Adult↗
PubMed1990

Treatment of attentional and hyperactivity problems in children with sympathomimetic drugs: a comprehensive review.

Issues concerning sympathomimetic drug treatment of children with attentional problems and hyperactivity are considered in light of cumulative and current research. These issues concern the atypical or "paradoxical" drug response of such children, predictability of drug response from neurological or biochemical assessments, and, especially, long-term outcome or effectiveness of sympathomimetic medication. Short-term drug effects on behavior and performance are well documented. However, follow-up studies that exist presently suggest little long-term impact of sympathomimetic drugs on school achievement, peer relationships, or behavior problems in adolescence. Questions remain concerning development of tolerance in children, ways to define subgroups of disordered children who may respond uniquely to stimulants, the efficacy of medication in combination with other treatments, and possible long-term negative consequences of medication.

Arousal↗
PubMed1990

Molecular cloning and characterization of a defective recombinant feline leukaemia virus associated with myeloid leukaemia.

The GM1 strain of feline leukaemia virus (FeLV) was isolated from a naturally occurring case of myeloid leukaemia and induces severe haematopoietic abnormalities, including myeloblastic leukaemia, on inoculation into cats. Molecular clones of FeLV-GM1 proviruses were obtained and studied by restriction enzyme mapping, blot hybridization and partial DNA sequence analysis. Two types of clone were isolated; the first was a replication-competent FeLV of subgroup A, resembling other low or minimally pathogenic FeLV-A isolates; the second was replication-defective with extensive deletions and mutations in gag and pol, although it has an intact env gene of subgroup B phenotype. Large segments of the defective proviruses, from the 5' leader sequence upstream of the gag gene to the 5' half of the env gene, show structural hallmarks of endogenous FeLV-related proviruses. Infectious FeLV-GM1 viruses recovered after transfection were tested for their leukaemogenic potential in newborn cats. Early polyclonal myeloproliferative changes were observed in cats inoculated with FeLV-A/GM1 alone, although these were more pronounced in animals receiving the full FeLV-AB/GM1 complex reconstituted by cotransfection of the defective virus FeLV-B with its FeLV-A helper. Analysis of viruses in the bone marrow showed that replication of the subgroup B component is delayed and restricted to a proportion of cats. Most of the infected cats developed persistent abnormalities of haematopoiesis and one progressed to disseminated myeloid leukaemia. The defective recombinant FeLV-B/GM1 appears to play an indirect but important role in myeloid leukaemogenesis.

Amino Acid Sequence↗