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Biomedical subjects

D M Prescott

Publications and source records attributed to D M Prescott.

At least 145 records · Page 8Linked to original sources
PubMed1967

Nuclear-cytoplasmic interaction in DNA synthesis.

In Amoeba proteus the transplantation of a nucleus engaged in DNA synthesis into a G(2)-phase (after DNA synthesis) cell results in inhibition of such synthesis. When the nucleus of a G(2) cell is transplanted into an S-phase (period of DNA synthesis) cell, such a nucleus may begin to synthesize DNA.

Amoeba↗
PubMed1967

Nucleolar and nuclear RNA synthesis during the cell life cycle in monkey and pig kidney cells in vitro.

The incorporation of 5-(3)H-uridine and 5-(3)H-cytidine into nucleolar and nonnucleolar RNA in the nucleus of monkey and pig kidney cells was measured in vitro during the cell life cycle. Time-lapse cinematographic records were made of cells during asynchronous exponential proliferation, in order to identify the temporal position of individual cells in relation to the preceding mitosis. Immediately following cinematography, cells were labeled with uridine-(3)H and cytidine-(3)H for a short period, fixed, and analyzed by radioautography. Since the data permit correlation of the rate of RNA labeling with the position of a cell within the cycle, curves could be constructed describing the rate of RNA synthesis over the average cell cycle. RNA synthesis was absent in early telophase, and rose very abruptly in rate in late telophase and in very early G(1) in both the nucleus and the reconstituting nucleolus. Thereafter, through the G(1) and S periods the rate of nuclear RNA synthesis rose gradually. When we used a 10-min pulse, there was no detectable change in the rate for nucleolar RNA labeling in monkey kidney cells during G(1) or S. When we used a 30-min labeling time, the rate of nucleolar RNA labeling rose gradually in pig kidney cells. With increasing time after mitosis, the data became more variable, which may, in part, be related to the variation in generation times for individual cells.

Animals↗
PubMed1967

Micronuclear RNA synthesis in Paramecium caudatum.

In a generation time of 8 hr in Paramecium caudatum, the bulk of DNA synthesis detected by thymidine-(3)H incorporation takes place in the latter part of the cell cycle. The micronuclear cycle includes a G(1) of 3 hr followed by an S period of 3-3(1/2) hr. G(2) and division occupies the remaining period of the cycle. Macronuclear RNA synthesis detected by 5'-uridine-(3)H incorporation is continuous throughout the cell cycle. Micronuclear RNA synthesis is restricted to the S period. Ribonuclease removes 80-90% of the incorporated label. Pulse-chase experiments showed that part of the RNA is conserved and released to the cytoplasm during the succeeding G(1) period.

Animals↗
PubMed1967

Proteins in nucleocytoplasmic interactions. I. The fundamental characteristics of the rapidly migrating proteins and the slow turnover proteins of the Amoeba proteus nucleus.

By the transplantation of amino acid-(3)H-labeled nuclei between cells and the subsequent isolation of nuclei for quantitative assay, we have confirmed that all the nuclear proteins of Amoeba proteus are divisible into two classes that are sharply defined by their physiological behavior. About 40% of the proteins in the nucleus rapidly migrates back and forth between the nucleus and the cytoplasm. These rapidly migrating proteins (RMP) are 25-50 times more concentrated in the nucleus than in the cytoplasm, and migration into the nucleus therefore occurs against a high concentration differential. The remaining 60% of nuclear proteins has been classified as slow turnover proteins (STP) since (as reported in a following paper) virtually all of them ultimately undergo turnover. Turnover in this context means loss of label from the nucleus, by either protein breakdown or protein migration to the cytoplasm. Isolation of nuclei in the detergent Triton X-100 results in a 20% loss of nuclear proteins but conclusions about RMP and STP were not found to be significantly affected by this loss.

Amino Acids↗
PubMed1966

Incorporation of nucleotides into nuclei of fixed cells by DNA polymerase.

The enzyme calf thymus polymerase requires denatured or single-stranded DNA as a primer for DNA synthesis and is inactive on native DNA preparations. The enzyme and tritium-labeled deoxyribonucleoside triphosphates were incubated with alcohol-fixed and Carnoy-fixed tissue preparations to see if primer DNA could be found in several types of cells undergoing DNA synthesis. In all cases, low-pH controls were prepared for comparison. Priming activity was not found in nuclei that had been fixed in alcohol. Priming activity was found in cell nuclei that had been fixed with an acid fixative or had been treated at a low pH prior to treatment with the enzyme reaction mixture.

Animals↗
PubMed1966

The syntheses of total macronuclear protein, histone, and DNA during the cell cycle in Euplotes eurystomus.

The syntheses of histone, total protein, and DNA during the cell cycle were measured in the macronucleus of Euplotes eurystomus by assaying the incorporation of tritiated amino acids and tritiated thymidine in groups of 800 to 1000 synchronized cells. The synthesis of DNA begins at 30% completion of the cell cycle, proceeds at a constant rate, and ends very shortly before the beginning of macronuclear division. Histone labeling is absent during G(1), begins in phase with DNA synthesis, continues at an unchanging rate during the S phase, and ends with the completion of DNA synthesis. The results support the view that the syntheses of histone and DNA are closely coupled events. Label in total protein accumulates at a constant rate during G(1) and appears to shift to a slightly higher rate when histone synthesis begins. At division, radioactive DNA, histone, and total protein are distributed equally between the daughter macronuclei without loss of radioactivity. Radioautographic analysis showed that protein labeling occurs throughout the macronucleus during the entire life cycle. There was no clear difference in the degree of protein labeling between replicated and unreplicated regions of the macronucleus. The distribution of label suggests that most of macronuclear protein labeling during the cell cycle is concerned with the events of transcription rather than replication.

Amino Acids↗
PubMedDate not supplied

The micronuclear gene encoding beta-telomere binding protein in Oxytricha nova.

The micronuclear version of the gene encoding beta-telomere binding protein (beta-TBP) in Oxytricha nova has been sequenced and compared to the macronuclear beta-TBP gene, previously described. The micronuclear gene contains three AT-rich internal eliminated sequences (IES) of 37, 40, and 43 bp and four macronuclear destined sequences (MDS). The IES interrupt the gene once near the 5' end of the coding region and twice in the 3' trailer downstream from the TGA stop codon. The sequences of the micronuclear and macronuclear genes are colinear. Thus, the micronuclear beta-TBP gene is not scrambled, which contrasts with the highly scrambled state among the 14 MDS in the micronuclear alpha-TBP gene.

Animals↗
PubMedDate not supplied

Internal eliminated segments (IESs) of Oxytrichidae.

Internal eliminated segments (IESs) are sequences that interrupt coding and noncoding regions of germline (micronuclear) genes of ciliated protozoa. IESs are flanked by short, unique repeat sequences, which are presumably required for precise IES excision during macronuclear development. Coding and noncoding segments of genes separated by IESs are called macronuclear-destined segments, or MDSs. We have compiled the characteristics of 89 individual IESs in 12 micronuclear genes in the Oxytricha and Stylonychia genera to define the IES phenomenon precisely, a first step in determining the origin, function and significance of IESs. Although all 89 IESs among the 12 different genes are AT-rich, they show no other similarity in sequence, length, position or number. Two main types of IESs are present. IESs that separate scrambled MDSs are significantly shorter and more frequent and have longer flanking repeat sequences than IESs that intervene between nonscrambled MDSs. A comparison of the nonscrambled gene encoding beta-telomere binding protein in three species of hypotrichs shows that even in the same gene IESs are not conserved in sequence, length, position, or number from species to species. A comparison of IESs in the scrambled gene encoding actin I in the three species shows that the evolutionary behavior of IESs in a scrambled gene may be more constrained. However, IESs in the scrambled actin I gene have shifted along the DNA molecule during evolution. In total, the various studies show that IESs are hypermutable in sequence and length. They insert, excise, and shift along DNA molecules more or less randomly during evolution, with no discernible function or consequences.

Animals↗
PubMedDate not supplied

Invention and mystery in hypotrich DNA.

Hypotrichs have evolved extraordinary ways of organizing, manipulating, and replicating the DNA in their micronuclear and macronuclear genomes. Short macronuclear DNA molecules containing single genes are created by excision from chromosomes, accompanied by massive elimination of the germline DNA sequences between genes. Germline genes themselves are interrupted by multiple noncoding segments called internal eliminated segments, or IESs, that divide genes into multiple macronuclear-destined segments, or MDSs. The functional significance of this organization is unknown. Over evolutionary time IESs accumulate mutations rapidly, are inserted into or excised from genes, and shift position along DNA molecules. MDSs are ligated to create functional genes when IESs are spliced out of micronuclear DNA during macronuclear development. MDSs in some germline genes are in scrambled disorder and become unscrambled in association with IES elimination. Replication of DNA in the macronucleus is accomplished by organization of replication enzymes and factors into a structure that sweeps through the macronucleus to replicate the many millions of gene-sized DNA molecules. The significance of many of the bizarre DNA phenomena in the evolutionary/functional success of hypotrichs is still unclear.

Animals↗
PubMedDate not supplied

The use of hydralazine to manipulate tumour temperatures during hyperthermia.

Hydralazine is an antihypertensive drug which theoretically could increase tumour temperatures during hyperthermia via reduction in tumour blood flow from a vascular 'steal' phenomenon. Doses that are therapeutically effective in reducing blood pressure in hypertensive patients would probably cause postural hypotension and other side-effects in normotensive patients beyond the hyperthermia treatment session, however. This study was designed to evaluate whether hydralazine, when administered at a safe dose for normotensive patients (0.125 mg/kg, i.v.) would be effective in increasing tumour temperatures during hyperthermia. The working hypothesis was that hydralazine at a dose of 0.125 mg/kg would be effective in raising tumour temperatures during hyperthermia treatment with minimal change in blood pressure. Fourteen human and five canine subjects were given hydralazine (0.125 mg/kg, i.v.) at the midpoint of a hyperthermia session. Temperatures and blood pressures were monitored before and after drug administration. Although hydralazine resulted in slight reduction in blood pressure, it was ineffective in increasing tumour temperatures in human patients (average maximum rise in median temperature was 0.26 +/- 0.32 degrees C). In canine subjects the same dose of hydralazine was effective in reducing blood pressure in four of five subjects studied (mean maximum drop was 22.7 +/- 4.1 mmHg) and the median temperature rose 0.8 +/- 0.7 degrees C. In the canine subjects the greater the decrease in blood pressure, the greater the increase in temperature. These results suggest that a rise in tumour temperature induced by hydralazine is dependent on creating a drop in blood pressure. Future studies in this laboratory will include tumour blood flow manipulation with antihypertensives which have a shorter half-life and a titratable effect. Using this approach, hypotension, which seems to be required to raise tumour temperature, will be more controllable in terms of magnitude and duration.

Animals↗
PubMedDate not supplied

Serious toxicity associated with annular microwave array induction of whole-body hyperthermia in normal dogs.

Using a regional annular microwave array it was possible to produce a systemic temperature of 42 degrees C in approximately 80 min with applied net power levels of approximately 150 W. Resulting temperature distributions were non-uniform. Sites within the array were above systemic temperature during heating but approximated systemic temperature during the plateau phase. Sites outside of the array were lower than systemic temperature during heating and plateau phases. Dogs allowed to recover from the procedure experienced severe toxicity consisting of lumbar muscle haemorrhage, pain and swelling, and pelvic limb paralysis. Histologically, there was severe myopathy and haemorrhage and oedema in neural tissue in the caudal lumbar spine. Acute necrosis of lymphoid tissue was observed in all dogs. Temperatures in muscle reached 43-46 degrees C and were higher than at other measured sites. Spinal canal temperatures were essentially equal to rectal temperature, approximating 42-43 degrees C during heating and plateau phases. These data suggest regionally induced whole-body hyperthermia may result in: (1) power deposition non-uniformity leading to muscle and spinal canal temperatures which exceed systemic temperature and which are sufficient to cause serious toxicity; (2) systemic temperature non-uniformity which is undesirable for systemic thermochemotherapy; and (3) possible immunological dysfunction associated with lymphoid necrosis. Extreme caution must be exercised in administering energy to localized regions of human patients with the intent of elevating systemic temperature.

Animals↗
PubMedDate not supplied

Manipulation of intra- and extracellular pH in spontaneous canine tumours by use of hyperglycaemia.

We evaluated the use of hyperglycaemia to reduce tumour pH in dog with spontaneous tumours. Dogs were randomized to two groups: control and glucose. Intravenous administration of 20% glucose was used to induce and maintain hyperglycaemia. Extra- and intracellular tumour pH were measured using interstitial pH microelectrodes and 31P-MRS, respectively. During the administration of glucose, the mean (+/- SEM) blood glucose concentration was 419.8 (+/- 32.8) and 121.1 (+/- 8.0) mg/dl for the glucose and control groups, respectively. The mean extracellular tumour pH before and following 90 min of hyperglycaemia was 7.15 (+/- 0.08) and 7.15 (+/- 0.09). During consecutive measurements, intracellular tumour pH did not change significantly for the control group or the group subjected to hyperglycaemic manipulation. In contradistinction to previous rodent studies, our results demonstrate that hyperglycaemia alone is not sufficient to manipulate either intra- (pHi) or extracellular (pHe) hydrogen ion concentration in spontaneous canine soft tissue tumours.

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