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Biomedical subjects

L Clayton

Publications and source records attributed to L Clayton.

At least 37 records · Page 2Linked to original sources
PubMed1995

Control of the surface expression of uvomorulin after activation of mouse oocytes.

Uvomorulin (E-cadherin) is the major cell adhesion molecule responsible for intercellular adhesion in early mouse embryos. In contrast to other cell adhesion molecules, it is not detectable on the cell surface until around 6 h after fertilisation or parthenogenetic activation, at the time when pronuclear formation occurs (Clayton, L., Stinchcombe, S.V. and Johnson, M.H., Zygote 1, 333-44, 1993). In order to investigate this developmental control of surface expression of uvomorulin, we examined the effects of inhibitors of various cellular processes on the appearance of uvomorulin at the oocyte surface, as assessed immunocytochemically. Inhibitors of cytoskeletal assembly (cytochalasin D and nocodazole), protein synthesis (puromycin and anisomycin), and DNA synthesis (aphidicolin) had no effect on surface expression. Brefeldin A, which inhibits intracellular transport and secretion, did prevent surface expression, but monensin did not. The effects of brefeldin were reversible; following 8 h of treatment, recovery of surface expression after removal of brefeldin began within 2 h. The time-course of surface expression post-activation suggested a link with pronuclear formation. However, when pronuclear formation was advanced experimentally using 6-dimethylaminopurine (DMAP), concomitant advancement of surface uvomorulin was not observed. Similarly, surface expression of uvomorulin did not accompany puromycin-induced pronuclear formation in maturing meiotic metaphase 1 (MI) oocytes in vitro. Thus, surface uvomorulin expression does not appear to be linked simply to pronuclear formation. Proteolytic processing of both newly synthesised and total uvomorulin to generate mature molecule from precursor increased within 30 min to 1 h after activation, and also occurred in the continued presence of brefeldin, suggesting that uvomorulin processing appears to be controlled independently of its surface expression.

Animals↗
PubMed1993

Comparison between colposcopic, cytologic, and histologic findings in women positive and negative for human papillomavirus DNA.

Little is known about the role of detection of human papillomavirus (HPV) DNA in exfoliated cells of the cervix in aiding the colposcopic diagnosis of cervical lesions. The purpose of our study was to compare the colposcopic findings of young women who were positive and negative for HPV DNA. Eighty-four women aged 13-22 years attending family planning clinics were examined colposcopically with the aide of acetic acid and Lugol's solution and without knowledge of HPV DNA status. Lesions identified were given scores based on the severity of observed colposcopic changes. Samples for cytology and HPV DNA testing, which included types 6, 11, 16, 18, 31, 33, and 35, were obtained at the time of the examination. Biopsies were performed on women with significant lesions identified on examination or with cytology suggestive of neoplasia. Students t-test and chi 2 analysis were performed to compare colposcopic variables and HPV DNA type. Of the 84 women examined, 17 were positive for HPV DNA; 9 had type 16/18. The average length of sexual activity was 2.7 years. Women with HPV 16/18 had a mean of 1.7 lesions visible at colposcopy compared to 0.7 lesions visible in those negative for HPV 16/18 (this included HPV DNA negative women and women positive for HPV types 6, 11, 31, 33, and 35) (p < 0.001). Women who were positive for HPV 16/18 also had higher lesional scores than the HPV 16/18-negative group (3.4 versus 1.0, respectively, p < 0.001). All four women who had dysplasia either on cytology or histology were positive for type 16/18.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Cell surface localisation and stability of uvomorulin during early mouse development.

We have examined immunocytochemically the subcellular distribution of the cell adhesion molecule uvomorulin in cleavage stage mouse embryos using conventional and confocal microscopy, under a range of detergent extraction and fixation regimes. Only traces of uvomorulin were detectable on the surface of unfertilised oocytes, whereas between 6 and 11 h after activation detergent-resistant surface expression was evident. This shift correlates with previously demonstrated changes in the pattern of synthesis and accumulation of uvomorulin from precursor state in unfertilised oocytes to mature protein after fertilisation. Embryos at subsequent stages up to the 8-cell stage exhibited a uniform distribution of uvomorulin on free surfaces and its concentration in regions of contact between blastomeres. At the 8-cell stage, during compaction, there was increased intercellular adhesion with concomitant accumulation of uvomorulin at intercellular contacts, whilst free surface uvomorulin was reduced and became relatively more susceptible to detergent extraction. When compact 8-cell embryos were decompacted in calcium-free medium, uvomorulin at contacts decreased while free surface and cytoplasmic staining increased. Blastomeres disaggregated from 4- and 8-cell embryos showed traces or 'footprints' of anti-uvomorulin staining in regions previously in apposition. These footprints disappeared over 45-60 min, during which time uvomorulin distribution became uniform. Possible mechanisms underlying the rearrangements which take place both at fertilisation and during compaction and experimental decompaction are discussed.

Animals↗
PubMed1993

Oxidant stress and glomerular prostanoid production: influence of angiotensin converting enzyme inhibition.

1. The effect of H2O2 (4.7 x 10(-9) -4.7 x 10(-3) M) on prostanoid production by isolated glomeruli from normotensive (WKY) and, spontaneously hypertensive rats (SHR) has been studied. 2. Oxidant stress significantly increased synthesis of prostaglandin E2 (PGE2), I2 (PGI2) and thromboxane A2 (TxA2) by glomeruli from both strains whereas the ratio (PGE2 + PGI2)/TxA2 increased in only SHR. 3. Pre-incubation of glomeruli with the angiotensin converting enzyme inhibitors captopril or lisinopril, had virtually no effect on H2O2-induced synthesis of individual prostanoids nor on the ratio (PGE2 + PGI2)/TxA2 by glomeruli from either WKY or SHR. 4. The findings suggest that H2O2-induced changes in glomerular function may be mediated, in part, by PGs but fail to support the suggestion that the ability of ACEI to protect glomeruli from H2O2-induced damage is determined by PGs.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1992

Synthesis and phosphorylation of uvomorulin during mouse early development.

The cell adhesion molecule, uvomorulin, is synthesised in both the 135 x 10(3) M(r) precursor and 120 x 10(3) M(r) mature forms on maternal mRNA templates in unfertilized and newly fertilized mouse oocytes. Synthesis on maternal message ceases during the 2-cell stage to resume later on mRNA encoded presumptively by the embryonic genome. Uvomorulin is detectable by immunoblotting at all stages upto the blastocyst stage, but shows variations in its total amount and processing with embryonic stage. Whilst only trace levels of phosphorylated uvomorulin are detectable in early and late 4-cell embryos, uvomorulin in 8-cell embryos is phosphorylated.

Animals↗
PubMed1992

Glomerular injury induced by hydrogen peroxide: modifying influence of ACE inhibitors.

The sensitivity of isolated glomeruli from normotensive (Wistar-Kyoto, WKY) and spontaneously hypertensive (SHR) strains to oxidant stress was studied by determining the incidence of pyknosis, karyohexis and karyolysis after incubation with different concentrations of hydrogen peroxide (H2O2) (4.7 x 10(-9) - 10(-3) M). Even though the proportion of glomeruli containing nuclei that demonstrated these features increased progressively with increasing concentrations of H2O2, the number of severely damaged glomeruli was relatively small even at concentrations of 4.7 x 10(-3) M. Examination of the surface epithelial cells of glomeruli using scanning electron microscopy revealed no evidence of disturbance of the macroscopic or podocyte structure or, of increased blebbing after H2O2-treatment. These data suggest damage to nuclei is an early result of ROS stress on glomeruli. Preincubation of WKY glomeruli with captopril or lisinopril resulted in a significant drop in the proportion of WKY glomeruli demonstrating structural damage after oxidant stress. In contrast, preincubation of SHR glomeruli with lisinopril had no effect on oxidant-induced changes in the morphology of SHR glomeruli, whereas captopril effected a significant increase in the proportion of glomeruli demonstrating damage at all concentration of H2O2.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1989

Successful use of clozapine in a patient with a history of neuroleptic malignant syndrome.

Reinstitution of antipsychotic medication is problematic in patients with a history of neuroleptic malignant syndrome (NMS). In this case, a patient with a history of probable neuroleptic malignant syndrome caused by administration, as single agents, of haloperidol, molindone, and lithium was later treated successfully with the novel antipsychotic clozapine. The propensity of various antipsychotic agents to cause NMS is discussed.

Activities of Daily Living↗
PubMed1989

Activation of the trk oncogene by alternatively spliced muscle and non-muscle tropomyosin sequences.

We have constructed a derivative of the trk oncogene in which the cytoskeletal tropomyosin sequences are replaced with skeletal muscle alpha-tropomyosin sequences derived from the same tropomyosin gene by alternative splicing. The biochemical and biological properties of this derivative are indistinguishable from those of the naturally occurring trk oncogene. Thus activation of the oncogenic activity of trk is a function of structural features of tropomyosin which are common to both skeletal muscle and non-muscle isoforms.

Animals↗
PubMed1988

Organization of the hTMnm gene. Implications for the evolution of muscle and non-muscle tropomyosins.

We have isolated clones of human genomic DNA which contain the structural elements of the hTMnm gene. In non-muscle tissue this gene produces a 2.5 kb (1 kb = 10(3) bases or base-pairs) mRNA encoding TM30nm, a 248 amino acid cytoskeletal tropomyosin. In muscle, alternative splicing of this gene results in the expression of a 1.3 kb mRNA encoding a 285 amino acid skeletal muscle alpha-tropomyosin. The hTMnm gene spans at least 42 kb of DNA and consists of 13 exons, only five of which are common to both the 2.5 kb and 1.3 kb transcripts. The boundaries of the exons giving rise to the muscle-specific isoform are identical to the base to those of other genes encoding muscle tropomyosins. A comparison of the structures of exons encoding the amino-terminal sequences of the muscle and non-muscle isoforms suggests that the hTMnm gene has evolved by a specific pattern of exon duplication with alternative splicing.

Amino Acid Sequence↗
PubMed1986

Amino acid sequence data of alpha-tubulin from myxamoebae of Physarum polycephalum.

About 96% of the amino acid sequence of an alpha-tubulin from the slime mould Physarum polycephalum has been determined. Of 430 sequenced amino acids, 30 differ from the deduced amino acid sequence of a recently published alpha-tubulin complementary DNA from the plasmodial form of P. polycephalum. The myxamoebal alpha-tubulin differs from all other known alpha-tubulins in one of the last three C-terminal amino acids that are Gly-Glu-Tyr instead of the usual Glu-Glu-Tyr. These last three amino acids are preceded by 11 residues that appear to be particularly susceptible to mutation. No heterogeneity was found whilst sequencing the myxamoebal alpha-tubulin, indicating that only one type of alpha-tubulin is present in myxamoebae. This alpha-tubulin appears to be less conserved than the previously described plasmodial alpha-tubulin, supporting the hypothesis that the structural constraints on tubulin in axonemes have a significant effect on its rate of mutation.

Amino Acid Sequence↗
PubMed1986

Amino-acid sequence data of beta-tubulin from Physarum polycephalum myxamoebae.

Starting with 7.7 mg of a beta-tubulin isolated from myxamoebae of the slime mould Physarum polycephalum, 90% of the sequence has been determined by the Edman degradation of peptides generated by cyanogen bromide, trypsin and Staphylococcus aureus protease. Differences to other beta-tubulins are mainly conservative and spread evenly throughout the chain except for a high concentration at the C-terminus. The Physarum beta-tubulin shows most homology to Chlamydomonas beta-tubulin (90.5%) and least homology to yeast beta-tubulin (S. cerevisiae, 73.4%). Two tryptic peptides were isolated in approximately equal quantities which were identical except in one position (S/ALTVPELTQRMFDA) showing that at least two beta-tubulins are present in myxamoebae. However, since this was the only heterogeneity found, these beta-tubulins are probably very similar.

Amino Acid Sequence↗
PubMed1986

Liquid-chromatographic analysis for cyclosporine with use of a microbore column and small sample volume.

This liquid-chromatographic assay requires 0.2 to 0.5 mL of whole blood, avoids the use of diethyl ether, and consumes only 10 to 20% of the solvents used in prior methods. Sample preparation involves an acidic extraction with methyl-t-butyl ether, performed in a 13 X 100 mm disposable glass tube, then a short second extraction of the organic phase with sodium hydroxide. After evaporation of the methyl-t-butyl ether, chromatography is performed on an "Astec" 2.0-mm (i.d.) octyl column. We compared results by this procedure with those by use of earlier larger-scale extractions and their respective 4.6-mm (i.d.) columns; analytical recoveries of cyclosporins A and D were comparable with previous findings and results for patients' specimens were equivalent, but the microbore columns provided greatly increased resolution and sensitivity.

Chromatography, Liquid↗
PubMed1985

Actin organization during the cell cycle in meristematic plant cells. Actin is present in the cytokinetic phragmoplast.

The distribution and organisation of F-actin during the cell cycle of meristematic root-tip cells of Allium was investigated using a rhodamine-labelled phalloidin to stain F-actin in isolated cell preparations. Such preparations could, in addition, be stained for tubulin by immunofluorescence, enabling a comparison between F-actin and microtubule distributions in the same cell. In interphase, an extensive array of actin-filament bundles was present in the cytoplasm of elongating cells, the bundles generally following the long axis of the cell and passing in close proximity to the nucleus. In contrast, the interphase microtubule array occupied the cortex of the cell and was oriented at right angles to the actin bundles. In smaller, isodiametric cells, microfilament arrays were present but less well developed. During cell division, phalloidin-specific staining was seen in the cytokinetic phragmoplast, and co-distributed with microtubules at all stages of cell plate formation; however, neither the pre-prophase band nor the mitotic spindle were stained with phalloidin. Co-distribution of F-actin and microtubules only occurs, therefore, at cytokinesis. The relationship between microfilaments and microtubules is discussed, together with the possible role of actin in the phragmoplast.

Actins↗
PubMed1985

Microtubule nucleating sites in higher plant cells identified by an auto-antibody against pericentriolar material.

Human scleroderma serum 5051, which is known to recognize the amorphous pericentriolar microtubule organizing center material of a variety of vertebrate cells, was found to immunostain spindle poles of meristematic higher plants from pre-prophase to late anaphase. Subsequently, during cytokinesis, staining was redistributed around the reforming telophase nuclei, but was not evident in the cytokinetic phragmoplast. At the transition between telophase and interphase, before the typical cortical interphase microtubule array was established, short microtubules radiated from the nucleus and in such cells the material recognized by 5051 was located around the daughter nuclei and not the cortex. These observations have led us to propose that the perinuclear region, or the nuclear surface, may function as a nucleation center for both spindle and interphase microtubules in higher plant cells.

Autoantibodies↗
PubMed1985

The cytoskeleton underlying side walls and cross walls in plants: molecules and macromolecular assemblies.

Plant cells organize their growth by reinforcing side walls during interphase (causing them to elongate) and by positioning and orienting the cross wall at cytokinesis. In the first part of this presentation we review progress made in identifying different cytoskeletal components that underlie side walls and that are involved in the deposition of the cross wall. During interphase, the cortical microtubule arrays co-distribute with an antigen recognized by a 'universal' monoclonal antibody to intermediate filaments. Using rhodaminyl-lysine-phalloidin no F-actin could be detected at the cortex but endoplasmic, axial cables were found. The cytokinetic apparatus--the phragmoplast--contains microtubules and we find that F-actin and the intermediate filament antigen also co-distribute with this array. We describe the three-dimensional arrangement of microtubules forming the interphase array in cells enlarging by both tip-growth and intercalary growth. In root hairs of higher plants and in apical cells of the filamentous stage of moss Physcomitrella patens, microtubules (MT) are detected at the apices and it is suggested from this that fragmentation of microtubules and absence of MTs from the tip are preparation artefacts. Using human serum from a scleroderma patient, possible microtubule nucleating sites are detected in meristematic cells; these segregate with the broad spindle poles and they surround the nucleus during early interphase--implying a peri-nuclear origin for the cortical MT array. The interphase microtubule array is described in terms of a dynamic helical model, which proposes: that the MT array is an integral complex; that microtubules form helices; that helices can change their pitch--the array converting to the various conformations.

Actins↗
PubMed1984

The relationship between the division plane and spindle geometry in Allium cells treated with CIPC and griseofulvin: an anti-tubulin study.

Isopropyl N-(3-chlorophenyl)-carbamate (CIPC), and griseofulvin, were used to perturb mitosis and the subsequent plane of division in meristematic cells of Allium cepa. The effects of these compounds on the microtubule organization throughout the cell cycle were investigated by immunofluorescence techniques. Microtubules were not disassembled by drug treatment, but the spindle organization was disrupted, resulting in tripolar spindles which gave rise to multiple nuclei. Ensuing cell plates, with associated phragmoplast microtubules, were branched. The effects of these drugs with respect to MTOC duplication and function in plant cells are discussed as is the relationship between the pre-prophase band (PPB) and the plane of cell division.

Cell Cycle↗