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Biomedical subjects

E Cooper

Publications and source records attributed to E Cooper.

At least 109 records · Page 6Linked to original sources
PubMed1983

HMG (high-mobility-group)-14/17-like proteins in calf thyroid. Thyrotropin-dependent phosphorylation and comparison with calf thymus proteins.

Two-dimensional polyacrylamide-gel electrophoresis of acid extracts of thyroid and thymus tissue, and of thyroid nuclei, revealed the presence of three HClO4-soluble nuclear proteins, PS.1, PS.2 and PS.3, whose electrophoretic mobilities closely resembled those of HMG (high-mobility-group) proteins 14 and 17. PS.1 co-migrated with HMG 14 on CM-Sephadex column chromatography. Like HMG 14, PS.2 and PS.3 were phosphorylated in calf thyroid slices; 32P-labelling of PS.3 was stimulated by thyrotropin. Thyrotropin also induced a rapid increase in the labelling of A5, an HMG-14/17-like protein found in whole calf thyroid and thymus tissue, but not in thyroid nuclei.

Animals↗
PubMed1983

Pertussis: herd immunity and vaccination coverage in St Lucia.

In a single complete epidemic in St Lucia, an island too small to support constant clinical pertussis, the pertussis case rates in small communities (villages and small towns) with differing levels of vaccination coverage of young children were compared. The association between greater vaccination coverage and greater herd immunity was clear, despite the imperfect protection given to individuals. An analysis in terms of population dynamics is evidence against the theory that endemic subclinical pertussis maintains transmission in a highly vaccinated population. We suggest that with a homogeneous vaccination coverage of 80% of 2-year-old children pertussis might be eradicated from the island, and that this is a practicable experiment.

Adolescent↗
PubMed1983

Effects of thyrotropin on thyroid chromatin. Enhanced sensitivity to micrococcal nuclease and increased nuclear protein phosphorylation.

Thyroid slices were incubated with or without TSH for 2 or 5 h. Nuclei were then prepared, subjected to mild digestion with micrococcal nuclease, and centrifuged at 1200 X g. The amount of DNA in 1200 X g supernatants was increased by TSH at 5 h, but not at 2 h. In parallel studies, thyroid slices were incubated with 32Pi and labeling of acid-soluble nuclear proteins was examined. TSH-dependent increases in labeling of histones H1 and H3, and of the high mobility group protein HMG 14, were observed at 2 h; however, there were no apparent changes in TSH-dependent labeling between 2 and 5 h, in nuclease-sensitive or in bulk chromatin. These results suggest that the observed TSH-dependent changes in the micrococcal nuclease-sensitivity of thyroid nuclear chromatin were not induced directly by changes in the phosphorylation of the histones or HMG 14.

Animals↗
PubMed1983

Thyroxine, 3,5,3' -triiodothyronine and 3,3', 5' -triiodothyronine in human amniotic fluid: relationships between concentrations and turnover.

We have made estimates of the possible contributions of various routes of entry and disposal to the turnover of thyroxine (T4), 3,5,3'-triiodothyronine (T3) and 3,3',5'-triiodothyronine (reverse T3, rT3) in human amniotic fluid (AF). Our calculations suggest that, in normal pregnancy, AF T4 and T3 are derived mainly from the maternal circulation, and that their concentrations depend very largely on binding-protein concentrations. The majority of AF rT3 is unlikely to enter the amniotic sac directly from the maternal circulation, or from the fetal circulation by passive diffusion or fetal urinary excretion; however, our calculations are consistent with the hypothesis it is derived largely from inner-ring deiodination of T4 in the fetal membranes. We propose that the molar ratio of one AF iodothyronine to another may yield more information about fetal thyroid status than the total concentration of any single iodothyronine.

Amniotic Fluid↗
PubMed1983

Conversion of thyroxine to 3,3',5'-triiodothyronine in the guinea pig placenta: in vivo studies.

Studies of placental inner-ring deiodination of T4 were carried out in pregnant guinea pigs, by in situ placental perfusion. When [131I]T4 and [125I]rT3 were administered to the mother, the ratio of fetal side to maternal side [131I]rT3 was more than 10 times greater than the corresponding ratio for [125I]rT3. When radiolabeled T4 was supplied to the fetal side of the placenta in perfusion fluid, and the perfusate recycled through the placental circuit, there was a progressive increase in labeled rT3 concentration in the perfusate. These results indicate that the guinea pig placenta actively deiodinates both maternal and fetal T4 in the inner ring in vivo. We found evidence of very little outer ring deiodination of either T4 or rT3. The quantitative contribution of placental deiodination of maternal T4 to circulating rT3 in the fetus appears to be small; however, placental deiodination of fetal T4 (about 0.5 nmol/kg fetal BW X day) could contribute significantly to fetal rT3 levels. Our observations are consistent with the hypothesis that placental inner-ring deiodination of T4 plays a part in the regulation of fetal iodothyronine metabolism.

Animals↗
PubMed1983

Effects of thyrotropin on the phosphorylation of histones and nonhistone phosphoproteins in micrococcal nuclease-sensitive and resistant thyroid chromatin.

Actively transcribed regions of chromatin are more susceptible than bulk chromatin to digestion by nucleases, and useful information about the composition and structure of active chromatin may be obtained by studying the chromatin fragments released from nuclei by limited nuclease digestion. In the present study, we have used micrococcal nuclease to investigate the effects of TSH on protein phosphorylation in nuclease-sensitive fractions of calf thyroid chromatin. Batches of calf thyroid slices were incubated for 2 h with 32Pi, with or without 50 mU/ml TSH. Nuclei were then prepared and the distribution of 32P-labeled histones, high mobility group (HMG) proteins, and other acid-soluble phosphoproteins between micrococcal nuclease-sensitive and resistant fractions of chromatin was examined. TSH increased the amount of 32P incorporated into HMG 14 and the histones H1 and H3. Hormone-dependent increases in the 32P-labeling of H1 and H3 were not selectively associated with micrococcal nuclease-sensitive chromatin. In contrast, [32P] HMG-14 was preferentially solubilized from nuclei by micrococcal nuclease. This lends support to the view that TSH-induced effects on the structure and function of transcriptionally active chromatin may be mediated in part by phosphorylation of HMG 14.

Animals↗
PubMed1982

Radioimmunoassay of thyroxine and 3,3',5'-triiodothyronine (reverse T3) in human amniotic fluid.

Measurement of amniotic fluid iodothyronine concentrations may enable antenatal detection of fetal thyroid abnormalities; however, the delineation of normal ranges is complicated by methodological problems associated with strong and highly variable protein-binding, and specificity of antisera. Improved radioimmunoassays of thyroxine (T4) and 3,3',5-triiodothyronine (reverse T3, rT3) have been developed to overcome these problems. In normal pregnancy, mean rT3 concentrations at less than 17 weeks, 17-22 weeks and 35-42 weeks gestation were 3.6 nmol/l (n = 21), 6.1 nmol/1 (n = 14) and 0.66 nmol/1 (n = 39) respectively; corresponding mean T4 concentrations were 2.4 nmol/1, 6.5 nmol/1 and 3.6 nmol/1. rT3 concentrations showed a strong positive correlation with T4 concentration in each age range; however, the molar ratio of rT3:T4 decreased progressively with gestational age, from 1.69 at less than 17 weeks to 0.19 at 35-42 weeks. In both mid- and late gestation, rT3 and T4 concentrations were strongly correlated with total amniotic fluid protein concentrations.

Amniotic Fluid↗
PubMed1982

Electrophysiological studies of new-born rat nodose neurones in cell culture.

1. Neurones of the nodose ganglion of the vagus nerve were dissociated from new-born rats and grown in the virtual absence of non-neuronal cells and in the presence of nerve growth factor. 2. The resting potentials of the neurones ranged from -40 to -80 mV. Action potentials were of short duration, with no inflexion on the falling phase; others were of longer duration with a hump on the falling phase. 3. The inward current of the action potential was carried either predominantly by Na+ or by Na+ and Ca2+. 4. Tetrodotoxin (1 microM) blocked the Na+ channels of some neurones but in other neurones the Na+ channels were partially or completely resistant to tetrodotoxin (1-10 microM). 5. Many neurones formed excitatory synapses on neighbouring neurones which were blocked or greatly reduced by conventional ganglionic nicotinic antagonists. This indicates that these neurones secreted ACh and expressed ACh receptors at these synapses. 6. The accompanying paper (Baccaglini & Cooper, 1981) reports the effect of co-culturing nodose neurones with non-neuronal cells on the expression of functional nicotinic receptors.

Acetylcholine↗
PubMed1982

Influences on the expression of acetylcholine receptors on rat nodose neurones in cell culture.

1. Nodose neurones dissociated from new-born rats were grown in culture in the absence or presence of cells from neonatal skeletal muscle or heart. 2. In cultures devoid of non-neuronal cells cholinergic interactions between the neurones were common. In the presence of non-neuronal cells such interactions were rare. 3. A decrease in the proportion of neurones responsive to ACh was primarily responsible for the reduced incidence of synaptic interactions. Non-neuronal cells influenced the expression of ACh receptors in developing nodose neurones in culture. 4. Most neurones appeared susceptible to the non-neuronal influence during the first week in culture. 5. Many nodose ganglion neurones, whether grown in the presence or absence of non-neuronal cells, were sensitive to gamma-aminobutyric acid and serotonin but were insensitive to glutamate, glycine and L-epinephrine.

Acetylcholine↗
PubMed1982

TSH stimulates 32P-labeling of thyroid nuclear HMG 14, a protein associated with actively transcribed chromatin.

Thyroid slices were incubated with 32Pi with or without TSH. 32P-labeling of acid-soluble nuclear proteins was then examined by two-dimensional polyacrylamide gel electrophoresis and autoradiography. We found that TSH enhanced the labeling of the high mobility group protein HMG 14, a protein that is preferentially associated with actively transcribed chromatin. This observation suggests that changes in HMG 14 phosphorylation may be involved in mediating TSH-induced effects on the structure and function of active chromatin.

Animals↗
PubMed1982

Effect of thyrotropin on the sensitivity of thyroid nuclear deoxyribonucleic acid to digestion by micrococcal nuclease.

Little is known about the mechanisms of action of polypeptide hormones on chromatin structure and nuclear function. We have employed micrococcal nuclease to examine the effect of TSH on the accessibility of DNA in thyroid nuclei. Brief digestion of nuclear suspensions with 0.05-0.2 U/ml micrococcal nuclease at 26-28 C decreased their opacity at 600 nm. The decrease in opacity was linear with increasing nuclear concentration up to 0.2 mg/ml DNA. This response to nuclease was enhanced in nuclear suspensions prepared from thyroid slices that had been incubated with TSH (50 mU/ml) for 5 h (P less than 0.001). To determine whether TSH also increased the digestion of DNA, we measured the amount of DNA released into 1200 X g supernatants by nuclease treatment of nuclei prepared from control and TSH-treated slices. When TSH-treated nuclei (110 micrograms/100 microliters) were digested with 0.2 U micrococcal nuclease/ml at 37 C for 30 sec, a mean of 12.6 micrograms +/- 3.6 (SD) DNA appeared in the supernatant, as compared to 8.4 micrograms +/- 1.98 DNA from control nuclei (P less than 0.05). This increase in the insensitivity of nuclear DNA to micrococcal nuclease may reflect some conformational change in chromatin in response to TSH. Since micrococcal nuclease sensitivity may reflect transcriptional competence of DNA, we speculate that polypeptide hormones may enhance the accessibility of DNA to RNA polymerase or to endogenous stimulators of transcription.

Animals↗
PubMed1981

Effect of thyrotropin on 32P-labelled histones H1 and H3 in specific populations of nucleosomes in the thyroid.

Thyrotropin (TSH) increases the labeling of histones of H1 and H3 in thyroid slices incubated with 32Pi. We have prepared nuclei from control and TSH-treated thyroid slices, digested them with micrococcal nuclease, and extracted specific populations of nucleosomes by salt fractionation. Mononucleosomes, derived from the most nuclease-sensitive regions of chromatin, appeared to be selectively enriched in 32P-labeled H1 and H3. However, we were able to detect TSH enhancement of H1 and H3 labeling only in nucleosome multimers derived from less nuclease-sensitive chromatin. Recent studies have indicated that transcriptionally competent regions of chromatin may be more susceptible to micrococcal nuclease digestion than inactive regions. Our results therefore suggest that H1 and H3 may be actively phosphorylated in transcriptionally competent chromatin; however, they suggest either that hormone-dependent phosphorylation of H1 and/or H3 does not confer transcriptional competence, or that not all transcriptionally competent chromatin is nuclease sensitive.

Animals↗
PubMed1981

Merkel cells as targets of the mechanosensory nerves in salamander skin.

Previous investigations showed that the morphological basis of the low-threshold rapidly adapting mechanoreceptors in the salamander skin is neurite-Merkel cell complex located in the epidermis. We have now examined whether sensory nerves are required for the appearance of Merkel cells, and whether these cells act as specific targets for ingrowing sensory axons. Electronmicroscopic examination of denervated skin shows that Merkel cells survive in normal density and appearance in the epidermis for at least six months without nerves. In addition, mechanosensory function of such skin is restored when the skin become reinnervated either by collaterally sprouting (intact) nerves or by regenerating ones, and Merkel cells are then found to have nerve terminals associated with them. These experiments suggest that Merkel cells do act as targets for ingrowing nerves in these circumstances. Further experiments were done on skin that had regenerated in the total absence of any innervation to the limb; such new skin contained nerve-free Merkel cells that were normal in appearance, density and location. When nerves were allowed to innervate this new skin the sensory axons grew to the "new" Merkel cells and established typical neurite-Merkel cell complexes, and normal mechanosensory function. Since the new skin had developed without nerves, the sensory axons were not following "old" pathways to the Merkel cells. We conclude that the Merkel cells are the true targets for the mechanosensory axons; these cells attract the sensory axons to them and/or contain specific markers that allow the ingrowing axons to recognize them. Once a Merkel cell becomes innervated it loses this "target cell" quality. In addition, mechanosensory function of the sensory endings appears to occur only when the endings have developed a morphological association with a Merkel cell.

Animals↗
PubMed1978

An immunological method for the purification of radiolabelled thyroxine.

A method for the removal of iodothyronine and iodide impurities from radiolabelled thyroxine is described. The principle of the method is to bind iodothyronine contaminants to specific antisera, and then to separate the antiserum-bound contaminants and iodide from the thyroxine by column chromatography. As reported here, the method is optimised for the removal of more than 98% of contaminating 3,5,3'-triiodothyronine and 99.8% of contaminating iodide from between 10 ng and 100 ng of thyroxine, where the molar ratio of thyroxine: 3,5,3'-triiodothyronine before purification is greater than or equal to 10:1. Recovery of purified thyroxine is more than 80%. The performance of the method is superior to that of preparative dialysis.

Animals↗