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N Maclean

Publications and source records attributed to N Maclean.

At least 55 records · Page 3Linked to original sources
PubMed1981

Structural transitions of chromatin in isolated Xenopus erythrocyte nuclei. II. Computer-based image analysis.

The morphology of isolated Xenopus erythrocyte nuclei is largely determined by the ionic constitution of the isolation medium. Electron microscopy of thin sections of nuclei isolated under varying ionic conditions has revealed four different morphological types with characteristic chromatin configurations. These nuclei have been used to study the condensation of chromatin within the confines of the nucleus. Electron micrographs of thin nuclear sections have been analysed by computer on the basis of their intensity of staining with lead citrate/uranyl acetate. The staining pattern (image analysis scan) is characteristic for each nuclear morphology and can be explained by a model which assumes that there are only four higher-order conformations that chromatin can adopt within the nucleus. These are present in varying amounts in the different nuclear types and an attempt has been made to equate the peaks identified by image analysis with previously-described chromatin structures. The results of this study serve to emphasize the potential of computer-based image analysis in the study of chromatin structure.

Animals↗
PubMed1980

Chromatin organization within nuclear blebs in leukocytes of Xenopus laevis.

The nuclei from leukocytes of peripheral blood, liver and spleen of an individual anaemic Xenopus laevis have been found to possess numerous nuclear blebs or projections. There structures were found to be very variable in size and shape as viewed in electron micrographs, but commonly included an enclosed mass of cytoplasm bound on one side by a very thin section of nuclear material. Such sections are membrane bounded on each side and frequently display an interesting ordered array of chromatin.

Animals↗
PubMed1979

Production and fate of erythroid cells in anaemic Xenopus laevis.

Adult Xenopus laevis, rendered anaemic by phenylhydrazine injection, have been studied during the recovery from such anaemia. Electron microscopy of liver and spleen sections indicates that both of these organs are active in the phagocytosis and destruction of the old damaged red blood cells. May-Grunwald and Giemsa staining of liver and spleen cells following anaemia has been used to show that erythropoiesis also occurs in both liver and spleen, and this has been confirmed by electron-microscope studies of these organs. Cell counting and radiolabelling of the new population of circulating erythroid cells in the period following phenylhydrazine injection suggests that a sudden release of basophilic erythroblasts from liver and spleen is followed by mitosis of this new cell population in circulation, and that no further release of erythroid cells from these organs is likely until complete recovery has occurred.

Anemia↗
PubMed1978

Studies of the template preference and other characteristics of the DNA polymerases of leukemic guinea pig lymphoblasts.

A single peak of DNA polymerase activity was detectable by phosphocellulose chromatography of leukemic guinea pig lymphoblast whole cell extracts. The inability to detect multiple peaks of activity as described with other cell types is shown to be due to the insolubility of a large proportion of the DNA polymerase activity under the extraction condition used. Multiple forms of DNA polymerase with different template specificities were recognized in extracts of the subcellular fractions of these cells after chromatography on phosphocellulose and DEAE cellulose. On Sephadex G-200 gel filtration these enzymes had apparent molecular weights in excess of 140,000 daltons. No RNA polymerase (reverse transcriptase) was detected in any subcellular fraction despite the presence of oncornavirus like particles in these cells.

Animals↗
PubMed1978

Feedback inhibition of erythropoiesis induced in anaemic Xenopus.

Serum from normal Xenopus, when injected into anaemic Xenopus, causes reduction in both DNA and protein synthesis in erythroid cells as indicated by in vitro culture of the blood cells. Experiments with erythrocyte-conditioned medium, reveal that this inhibitory substance can be recovered from mature erythrocytes. Sephadex G-25 fractionation of normal serum and haemolysate demonstrates that the inhibitory factor consists of molecules of low molecular weight, and experiments with with cells of Xenopus kidney reveal that the feedback inhibition may be tissue specific to erythroid cells.

Anemia↗
PubMed1978

Biochemical changes in developmentally retarded Xenopus laevis larvae. I. The lens crystallin transition.

Premetamorphic tadpoles of Xenopus laevis reared in water containing 0.01% propylthiouracil are developmentally retarded and metamorphosis is prevented. When uncrowded, they continue to grow to a giant size. Moderate crowding leads to a slower rate of growth. Thus morphologically premetamorphic tadpoles were produced with lens diameters appropriate to either normal premetamorphic, climactic or post-metamorphic animals. The lens crystallins of such tadpoles have been separated by immunoelectrophoresis and polyacrylamide gel electrophoresis. The crystallin pattern was correlated with lens diameter rather than with body stage. Giant retarded larvae possessed crystallin patterns identical to those or normal adults. The thyroid antagonist propylthiouracil is therefore unable to prevent the lens crystallin transition, the beginning of which is normally temporally correlated with metamorphosis.

Animals↗
PubMed1977

The role of the surviving pancreas in late fatalities of acute pancreatitis.

The necropsy findings in 3 patients who died between 4 and 14 weeks after episodes of acute pancreatitis are described. The most striking features were the extent of extraperitoneal necrosis and the comparative normality of residual portions of the pancreas. It is suggested that when the duct system is disrupted, the secretions of the surviving pancreas cause progressive enzymatic destruction of extrapancreatic tissues and thus contribute to the mortality of the disease.

Acute Disease↗
PubMed1977

Studies on the template activity of 'isolated' Xenopus erythrocyte nuclei. II. The effects of cytoplasmic extracts.

The effects of exposing nuclei isolated from Xenopus erythrocytes to cytoplasmic extracts prepared from various sources on their template activity are described. The cytoplasm of rat liver cells and the immature blood cells of Xenopus contain factors which stimulate RNA synthesis in these essentially inactive nuclei, whereas the cytoplasm of many other cells does not yield such factors. The active factors in rat liver cytoplasmic extracts appear to be proteins of molecular weight about 40000 Daltons. The implications of these results for genetic control in eukaryotes are discussed.

Animals↗
PubMed1977

Transcriptional reactivation of isolated Xenopus erythrocyte nuclei: patterns of RNA synthesis.

Nuclei isolated from Xenopus erythrocytes can be transcriptionally reactivated by exposure to certain cytoplasmic proteins. The types of RNA synthesized during this reactivation have been studied and compared with those present in, or synthesized by, isolated nuclei not so reactivated or in entire Xenopus erythrocytes. In all cases, the pattern of transcription indicates the synthesis of a broad range of low molecular weight RNAs. Competitive hybridization demonstrates that the reactivated nuclei synthesize some transcripts not normally produced by the isolated nuclei and we have shown that a proportion of these possess amino acid-accepting activity. The significance of these results is discussed in relation to the control of gene activity in these cells.

Amino Acids↗
PubMed1976

Carcinoma of the male breast: report of a series of 88 cases.

A series of 88 cases of male breast cancer was compared with 241 cases of female breast cancer randomly selected from Departmental records. Cases of male breast cancer differed significantly from control female cases with regard to stage of the disease, age of onset and liability to the development of a second carcinoma. In 11 of the 88 cases (12.5%) of male breast cancer another primary malignant tumour developed. In seven instances the large bowel or rectum was the site of the other carcinoma. When correction was made for age and for the stage of the disease the prognosis of breast cancer in men and women was found to be similar. Only minor histological differences were found between male and female cases. Two of 54 cases examined for X-chromatin proved to be Barr-positive.

Adult↗
PubMed1976

DNA polymerase activity in plasma from leukaemic guinea-pigs.

Measurement of DNA polymerase in leukaemic guinea-pig plasms reveals the presence of low levels of sedimentable and non-sedimentable enzymic activities. Since the sedimentable DNA polymerase is ribonuclease sensitive, uses poly(C).oligo(dG) as template, and bands in a sucrose density gradient at 1-17 g/ml it is thought to be the GPLV-associated reverse transcriptase. The soluble DNA polymerase is stimulated by ribonuclease and is probably of cellular origin.

Animals↗
PubMed1976

Cytogenetics and infertility in man. II. Testicular histology and meiosis.

Within a group of 207 subfertile men, selected for testicular biopsy, histological investigations were made successfully in 194 chromosomally normal and 7 chromosomally abnormal individuals. Fifty-two per cent of men with a normal karyotype showed normal testicular histology, 31% showed a general depression of spermatogenesis and 8% showed deficiency in the late stages. Ten per cent had only Sertoli cells in the testis. The range of testicular conditions seen in the chromosomally abnormal men was similar to that found in the chromosomally normal. Meiotic studies carried out on 118 chromosomally normal individuals gave a mean chiasma count of 48-9 per cell. There was a positive correlation between high numbers of cells at diakinesis/metaphase I showing X and Y univalents and low numbers of cells reaching metaphase II. Meiosis was studied in 3 translocation heterozygotes, one 47, XYY male, one 47, XY+mar individual and one patient with a ring Y chromosome.

Adult↗
PubMed1975

The erythroid cells of anaemic Xenopus laevis. I. Studies on cellular morphology and protein and nucleic acid synthesis during differentiation.

Phenylhydrazine has been used to induce anaemia in Xenopus laevis. The dosage used causes the complete destruction of all mature erythrocytes within twelve days. The anaemia results in the initiation of a wave of erythropoiesis and large numbers of immature erythroid cells are released into the circulation. The morphological and biosynthetic changes which these cells undergo as they differentiate in circulation are described. The origin of the circulating erythroid cells is also discussed.

Anemia↗
PubMed1975

The erythroid cells of anaemic Xenopus laevis. II. Studies on nuclear non-histone proteins.

The mass ratio of nuclear non-histone protein: DNA in the immature circulating erythroid cells of phenylhydrazine-induced anaemic Xenopus is approximately threefold higher than in mature erythrocytes. This is largely due to the presence of increased amounts of low and intermediate molecular weight proteins in the nuclei of the immature cells. There are a few qualitative differences in the components of this class of proteins between the mature and immature cells, the most notable of which is the presence of a protein of molecular weight approximately 115000 in the former which is not detectable in the latter. These changes are discussed in relation to the changing synthetic capacities of cells and to certain generalizations about the function of the nuclear non-histone protein based on studies of other differentiating systems.

Anemia↗