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Biomedical subjects

E A Thompson

Publications and source records attributed to E A Thompson.

At least 145 records · Page 8Linked to original sources
PubMed1986

Proteolytic cleavage of human von Willebrand factor induced by enzyme(s) released from polymorphonuclear cells.

In vivo fragmentation of the von Willebrand factor antigen (vWF:Ag) molecule has been demonstrated on radiocrossed immunoelectrophoresis (CIE) in the plasma from patients with disseminated intravascular coagulation, in factor VIII concentrates, and in normal serum. Experiments reported here show that polymorphonuclear (PMN) cells contain a non-calcium-dependent protease(s) that when released and incubated with vWF:Ag results in an additional vWF:Ag peak on radio-CIE. Production of fragments of vWF:Ag by incubation with PMN cells occurred in a time-dependent manner. The protease(s) responsible was inhibited by diisopropyl fluorophosphate, soybean trypsin inhibitor, and aprotinin, but not by benzamidine, azide, epicron, or hirudin. Citrate, EDTA, and leupeptin also had no effect on the PMN cell enzyme's activity, indicating that the enzyme(s) is not calcium dependent. The PMN cell enzyme responsible for vWF:Ag fragmentation is located intracellularly and released by freezethaw lysis or cell activation by calcium or the calcium ionophore A23187.

Aprotinin↗
PubMed1985

Transfection of mouse ribosomal DNA into rat cells: faithful transcription and processing.

Truncated mouse ribosomal DNA (rDNA) genes were stably incorporated into rat HTC-5 cells by DNA-mediated cell transfection techniques. The mouse rDNA genes were accurately transcribed in these rat cells indicating that there is no absolute species specificity of rDNA transcription between mouse and rat. No more than 170 nucleotides of the 5' nontranscribed spacer was required for the accurate initiation of mouse rDNA transcription in rat cells. Further, the mouse transcripts were accurately cleaved at the 5' end of the 18S rRNA sequence, even though these transcripts contained neither the 3' end of mouse 18S rRNA nor any other downstream mouse sequences. Thus, cleavage at the 5' end of 18S rRNA is not dependent on long range interactions involving these downstream sequences.

Animals↗
PubMed1985

Hormonal regulation of transcription of rDNA: glucocorticoid effects upon initiation and elongation in vitro.

Various parameters of transcription of cloned mouse rDNA have been examined using extracts from control P1798 cells and from cells treated 24 h with 0.1 microM dexamethasone. Highly purified RNA polymerase I from either source catalyzes nucleotidyl transfer (elongation) at a rate of approximately 30 nucleotides/sec. Extracts from hormone-treated cells are capable of forming stable, preinitiation complexes. The rates of stable complex formation are the same in extracts from control and hormone-treated cells. Nevertheless, initiation of transcription does not occur in extracts from hormone-treated cells. Initiation in such extracts may be restored by the addition of a partially purified RNA polymerase I initiation factor, designated TFIC. The data indicate that initiation by RNA polymerase I is a multi-step process. The first step involves the formation of stable, preinitiation complexes, as demonstrated by a number of groups. Initiation, per se, requires an additional protein, TFIC. Glucocorticoids and perhaps other mitogenic agents regulate transcription of rDNA by influencing the amount or activity of TFIC.

Animals↗
PubMed1985

The history of a lethal X-linked mutant.

Much attention has recently been focused upon the role of linkage analysis in genetic counselling, and enthusiasm has led to some misleading claims. While linkage analysis will undoubtedly play an important role for traits where there are extensive pedigrees of cases, it can achieve nothing where each case is the sole appearance of a mutation. The situation for a lethal recessive X-linked trait lies, in probabilistic terms, close to this latter extreme, particularly in the current world of small families. In view of current practice and research, it seems important to have a precise quantitative assessment of the patterns of carriers and cases generated by such an X-linked lethal mutation, with particular reference to the problem of Duchenne muscular dystrophy. In this paper a branching-process analysis is used to provide such an assessment. This approach has the advantage of requiring neither possibly unrealistic equilibrium assumptions nor assumptions about mutation rates. It also allows the effects of a variety of family size distributions to be analysed. It is found that an X-linked recessive lethal mutation produces few cases (if any), and will do so within a very few generations of its occurrence. Within the usual range of modern family size distributions the mean time to appearance is remarkably constant. The mean number of carriers at the time of the first case is small, as is the expected number of future cases. Except where the family size distribution has large variance, a high proportion of cases are the first in their family.

Biometry↗
PubMed1984

Hormonal regulation of transcription of rDNA: use of nucleoside thiotriphosphates to measure initiation in isolated nuclei.

Nuclei isolated from cultured mouse and rat cell lines initiated pre-rRNA chains at the correct site and with the correct nucleotide specificity (A for mouse, G for rat). Nucleic acid filter hybridization and S1 nuclease mapping were used to analyze the RNA products initiated with nucleoside (beta-S)triphosphates. Initiation of pre-rRNA was completely resistant to alpha-amanitin but was inhibited by either actinomycin D or heparin. Experiments with P1798 mouse lymphoma cells indicated that the antiproliferative effects of glucocorticoids on lymphoid cells includes a reduction in the ability of nuclei to initiate pre-rRNA chains.

Adenosine Triphosphate↗
PubMed1984

Interpretation of LOD scores with a set of marker loci.

The problem discussed is that of interpreting LOD scores when multiple markers are tested for linkage with a particular disease locus. Provided the tests are based on independent segregations, both the maximum and the average LOD can be translated into a score that would have the same significance level were it the result of a single test.

Biometry↗
PubMed1984

Possible linkage of a breast cancer-susceptibility locus to the ABO locus: sensitivity of LOD scores to a single new recombinant observation.

We present evidence of a pedigree in which a major gene for breast cancer-susceptibility appears to segregate in a dominant fashion. Linkage analysis suggests that the breast cancer-susceptibility locus in this family may be linked to the ABO locus, which is located on band q34 of chromosome 9. At an early stage in the analysis, a LOD score of 3.0 for zero recombination was obtained for linkage between ABO and the susceptibility locus, but a single recombinant reduced the LOD score to 1.72 at a recombination fraction of 0.06. A final observation of a nonrecombinant brings the LOD score for this pedigree to 1.99 at theta = 0.05. We attempt to put these results in perspective by discussing the sensitivity of the LOD score to the next observation. Examples of the volatility of LOD scores are given. These simple calculations show that tight linkage represents the worst case for the interpretation of a LOD score of 3.0. Finally, we discuss the linkage between the breast cancer-susceptibility locus and the ABO blood group and approaches to confirming or denying this result.

ABO Blood-Group System↗
PubMed1984

Isolation and characterization of lymphosarcoma P1798 variants selected for resistance to the cytolytic effects of glucocorticoids in vivo and in culture.

Clonal subpopulations of lymphosarcoma P1798 have been subjected to glucocorticoid selection in vivo and in culture and the glucocorticoid binding and responsiveness of the resistant variants have been compared with those of the parental lines. Cell populations that are resistant to the cytolytic effects of glucocorticoids in vivo exhibit a slightly reduced level of glucocorticoid binding, although nuclear translocation of the hormone-receptor complex is not reduced. Sensitive and resistant tumors exhibit similar kinetics of hormone uptake and dissociation following a single injection of dexamethasone. Selection for glucocorticoid resistance in vivo does not result in an increase in the modal number of chromosomes. Cells that are resistant to the cytolytic effects of glucocorticoids in vivo are completely sensitive to the antiproliferative effects of glucocorticoids in culture. Moreover, dexamethasone increases the expression of mouse mammary tumor provirus in cytolysis-resistant and sensitive cells both in vivo and in culture. Selection for glucocorticoid resistance in culture yields variants with decreased glucocorticoid binding and/or nuclear translocation of the hormone-receptor complex. These cells appear to express classical receptor-defective phenotypes. Nevertheless, cells that are resistant to glucocorticoids in culture undergo cytolysis when treated with glucocorticoids in vivo. These data indicate that, under certain circumstances, different mechanisms may be involved in loss of glucocorticoid responsiveness in vivo and in culture.

Animals↗
PubMed1984

Glucocorticoid inhibition of initiation of transcription of the DNA encoding rRNA (rDNA) in lymphosarcoma P1798 cells.

Cell-free extracts of lymphosarcoma P1798 cell culture lines support faithful initiation upon the cloned mouse DNA encoding rRNA (rDNA) promoter, whereas extracts from cells treated for 16 hr with 0.1 microM dexamethasone cannot. Extracts from both sources transcribe the cloned 5S RNA gene in vitro and mixing experiments further demonstrate that inhibition of transcription of rDNA in vitro is not due to nucleases or inhibitors of transcription present in extracts from glucocorticoid-treated cells. Incubation of extracts from control cells at 45 degrees C for 15 min inactivates RNA polymerase I and abolishes transcription. Activity can be restored by the addition of partially purified RNA polymerase I from control cells and hormone-treated cells. Moreover, extracts from hormone treated cells can be reconstituted by the addition of a partially purified, heat-stable transcription factor from control cells.

Animals↗
PubMed1984

Information gain in joint linkage analysis.

The advent of DNA sequencing and the prospect of the availability of very large numbers of marker loci have reawakened interest in linkage studies. Statistical analyses of linked genetic loci have previously been based on pairwise analysis of the loci, and/or have assumed a known ordering of them along the chromosome. For the sizes of sample available in human medical genetics, pairwise analysis may be a statistically inefficient and inconclusive procedure. It is shown that three-way data provide very much more information, particularly with regard to the problem of ordering the loci. Correct answers to questions of locus order are of particular importance in current approaches to fetal diagnosis, where counselling is based on genotypes at markers closely linked to a disease locus. Although the three-locus analysis of this paper is only a first step towards joint analysis of multilocus data, the qualitative form of the data is of the joint pattern of cosegregation of loci. The pairwise counts of recombinants and nonrecombinants used for pairwise analysis are both qualitatively and quantitatively less informative. Many practical and theoretical problems of multilocus analysis of data remain to be solved, but the practical importance of doing so is demonstrated.

Animals↗
PubMed1984

Transcription of the mouse ribosomal spacer region.

This paper describes experiments designed to test the hypothesis that DNA sequences upstream from the mouse rRNA promoter are transcribed in vivo or in vitro. Plasmid pB28 contains a SalI restriction fragment that extends from -169 to -1,894 base pairs, with respect to the origin of transcription of pre-rRNA. Labeled RNA synthesized in intact cells does not hybridize to this region. Neither S1 nuclease mapping nor RNA dot blot hybridization revealed the presence of sequences complementary to this region. Transcriptional studies carried out in vitro indicated that this region is not transcribed under conditions that are optimal for utilization of the authentic rRNA promoter. Moreover, this region does not appear to form stable transcription complexes with RNA polymerase I transcription components. These data indicate that the mouse rDNA repeating unit differs from those of Xenopus spp. and Drosophila melanogaster in that reduplicated RNA polymerase I promoters are not found in the mouse rDNA spacer region.

Animals↗
PubMed1983

Gene extinction and allelic origins in complex genealogies.

With the increasing emphasis on data analysis in mathematical genetics, problems of parametrizing genealogical structure become of practical importance. A complete specification of the genetic effects of genealogical structure is provided by the probabilities of genetically distinct states of gene identity by descent. Although this provides a direct parametrization for the joint distribution of traits on a set of related individuals, it is an unwieldy tool in the analysis of large and complex genealogies. Probabilities of joint descent of founder genes and likely ancestries of alleles provide alternative characterizations of relationship and have direct application in practical problems. Joint extinction probabilities of founder genes can also be derived as ancestral likelihoods: evolutionarily, the most significant characteristic of a genealogical structure must be its effect on the survival and extinction of genes.

Alleles↗
PubMed1983

Hormonal regulation of transcription of rDNA. Inhibition of transcription during glucocorticoid-mediated inhibition of proliferation of lymphosarcoma P1798 cells in culture.

A lymphosarcoma cell line designated P1798.S6M has been characterized with respect to glucocorticoid responsiveness in culture. Cells ceased to proliferate in the presence of 10(-7) M dexamethasone. Cell viability remained high and glucocorticoid-sensitive cells could be rescued from cultures treated with dexamethasone for 24 or 48 h. These data indicate that P1798.S6M undergoes reversible arrest in the presence of dexamethasone. The system was used to study the effects of mitotic arrest upon transcription of rDNA. Incorporation of [methyl-3H]methionine into rRNA was rapidly inhibited and pulse-chase experiments indicated that 28 S RNA was not synthesized after 24 h of exposure to dexamethasone. Hybridization studies indicated that the amount of pre-rRNA was reduced by 90 to 95% in cells treated for 24 h. Transcription studies were carried out in isolated nuclei. Twenty-four hours after addition of dexamethasone, template-bound RNA polymerase I activity decreased by 89 to 96%. Total RNA polymerase I activity did not decrease, whereas disengaged nuclear polymerase I activity increased dramatically. Filter hybridization studies indicated that labeling of nascent pre-rRNA chains in vitro was inhibited 93%. These data are interpreted as follows: Dexamethasone reversibly inhibits proliferation of P1798.S6M cells and transcription of rDNA. Total RNA polymerase I activity does not decrease, but the amount of template-bound enzyme is reduced with a concomitant increase in the amount of disengaged polymerase I. This indicates that initiation of transcription is inhibited in cells undergoing mitotic arrest in the presence of dexamethasone.

Animals↗
PubMed1983

Optimal sampling for pedigree analysis: parameter estimation and genotypic uncertainty.

Many problems of sampling strategy arise in pedigree analysis. Although specific questions have been previously considered, there is a need for a general study of the form of the likelihood surface for genetic models. Were genotypes observable, the log-likelihood would have a very simple form. The two classes of factors of genealogical structure affecting general questions of inference are thus those (such as inbreeding or assortive mating) which affect the genotype distribution within a pedigree, and those affecting the extent to which these unobservable genotypes can be inferred from phenotypes. The latter aspect is considered in some detail.

Female↗
PubMed1983

A recursive algorithm for inferring gene origins.

Kidd et al. (1980) studied the allelic origins of a recessive trait in an extensive and complex genealogy. Due to computational limitations, the hypotheses they could consider were limited, and the dependencies in descent from alternative ancestors and to different sibships were not considered. Karigl (1981) developed a recursive algorithm for the computation of multiple kinship coefficients. Here we show that very similar algorithms apply to probabilities of the joint descent of multiple genes from specified ancestral genes. This makes possible a far more extensive analysis of hypotheses of allelic origins in a genealogy.

Alleles↗