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Biomedical subjects

R Holliday

Publications and source records attributed to R Holliday.

At least 91 records · Page 5Linked to original sources
PubMed1989

A molecular approach to the problem of positional information in eggs and early embryos.

It is proposed that long maternal RNA transcripts, which are known not to be translated, have a positive role in defining positional information in the egg or early embryo of invertebrates and vertebrates. The sequences of these RNAs can, in principle, provide a large store of morphogenetic information in two and three dimensions specified by the primary sequence in DNA. This could occur by complementary base pairing within and between molecules to build up in stages a large three-dimensional scaffold or cytoskeleton stabilized by proteins. This would define specific regions or compartments in the egg, and embryonic nuclei would be distributed to different cytoplasmic environments. The RNA and associated proteins would provide the basis for specific interactions with nuclear DNA, including the transport of DNA binding proteins to the nucleus and the activation of latent mRNA molecules associated with the RNA-protein scaffold. Such interactions would produce the specific gene expression required for further embryonic development. Some features of early development of a few well studied species are briefly discussed in relation to the proposed mechanism for RNA specification in space.

Animals↗
PubMed1988

Psychosocial considerations in gastric stapling surgery.

Thirty-one morbidly obese patients awaiting gastric stapling and 31 similar patients who had already undergone this procedure were evaluated using four psychological self-report questionnaires: Eating Disorder Inventory, Millon Clinical Multiaxial Inventory, Locus of Control, and a questionnaire developed by the authors. The subjects were predominantly female, had a strong family history of obesity, and reported anxiety in the pathological range. The overall results suggest that, while not a panacea, gastric stapling does confer significant benefit to morbidly obese individuals.

Adult↗
PubMed1988

Relationship among CT scans, neurological exam, and neuropsychological test performance in right-brain-damaged stroke patients.

Right-hemisphere stroke rehabilitation inpatients were assessed by: (1) CT scans; (2) neurological exam; and (3) cognitive and affective psychometric measures. Damage to temporal, parietal, and occipital regions was associated with visual-spatial impairments. Surprisingly, parietal damage was no more related than temporal and occipital damage to severity of visual inattention. While the neurologist's ratings of lability and depression were related to CT-scan measures, patients' self-report of depression was not so related. These findings support a less specific and probably greater interlobule organization of the right, as compared with left, hemisphere, and highlight the need for multifaceted affective assessment in such a brain-damaged group.

Brain↗
PubMed1987

The inheritance of epigenetic defects.

Evidence from many sources shows that the control of gene expression in higher organisms is related to the methylation of cytosine in DNA, and that the pattern of methylation is inherited. Loss of methylation, which can result from DNA damage, will lead to heritable abnormalities in gene expression, and these may be important in oncogenesis and aging. Transformed permanent lines often lose gene activity through de novo methylation. It is proposed that epigenetic defects in germline cells due to loss of methylation can be repaired by recombination at meiosis but that some are transmitted to offspring.

Aging↗
PubMed1987

DNA methylation and epigenetic defects in carcinogenesis.

It is frequently assumed that DNA-damaging agents are carcinogenic because they induce mutations. However, another strong possibility is that the damage leads to heritable changes in the methylation of cytosine in DNA. Considerable evidence exists that gene expression in mammalian cells is in part controlled by methylation of specific DNA sequences. Carcinogens may act by altering the normal epigenetic controls of gene activity in specialised cells, and thereby produce aberrant heritable phenotypes. It is known that agents which inhibit DNA methylation can be carcinogenic and that tumour cells are altered in DNA methylation.

Animals↗
PubMed1987

Gene reactivation: a tool for the isolation of mammalian DNA methylation mutants.

We report the isolation and characterization of a mammalian strain (tsm) that has a temperature-sensitive mutation in DNA methylation. The isolation procedure was based on the observation that treatment of a CHO TK- MT- cell line with demethylating agents introduces up to 46% demethylation, resulting in phenotypic reversion and transcriptional activation of the thymidine kinase (TK) and metallothionein (MT) genes at frequencies ranging from 1% to 59%. Seven thousand individual colonies from an EMS-mutagenized CHO TK- MT- population were screened for spontaneous reversion to TK+ phenotype after treatment at 39 degrees C. Successful isolates were subsequently examined for MT+ reversion. A single clone (tsm) was obtained that showed temperature-dependent reactivation of both TK and MT genes at frequencies of 7.2 X 10(-4) and 6 X 10(-4), respectively. The tsm cells were viable at 39 degrees C and showed no increased mutation frequency. Reactivation correlated with transcriptional activation of the respective genes, whereas backreversion to the TK- phenotype was associated with transcriptional inactivation. TK- backrevertants were reactivable again with demethylating agents. Although demethylation in tsm cells was not detectable by HPLC, Southern blot analysis revealed that reactivants, irrespective of their mode of generation, showed specific demethylation of both TK and MT genes. Also, after about 150 cell generations after treatment, reactivants from both temperature-induced tsm and cells exposed to demethylating agents gained 60% and 23%, respectively, in 5-methylcytosine (5mC). It is proposed that the phenotype of tsm cells is due to a mutation involved in the regulation of DNA methylation. The further characterization of this and other mammalian mutants should help to clarify the physiological role of DNA methylation, as well as its regulation.

Animals↗
PubMed1986

The susceptibility of Werner's syndrome and other human skin fibroblasts to SV40-induced transformation and immortalization.

In attempts to transform and immortalize human cell cultures, skin fibroblasts from normal donors of different ages, from patients with the premature ageing diseases Werner's syndrome (WS) and progeria (PR), and from donors with the cancer-prone diseases ataxia telangiectasia (AT), Bloom's syndrome (BS) and Fanconi's anaemia (FA), were infected with SV40 virus and their growth monitored thereafter. Lesch-Nyhan (LN) fibroblasts were also infected. SV40-infected cultures from two normal and from WS, AT and LN donors attained a spectrum of transformed properties, high mitotic activity at confluence, presence of T-antigen, anchorage independence and altered morphology. Most of these pretransformed cultures died in the crisis period. However, two cultures from the WS and LN patients survived the crisis period and have now been grown to more than 200 passages. For the LN culture the crisis period was at least 200 days. Both permanent lines retain the properties of pretransformed cells, but differ in their modal chromosome number and ability to grow in methionine-free medium. It can be concluded from these experiments that transformation by SV40 to permanent lines is a rare event in human skin fibroblasts, even when these cells were taken from patients predisposed to form cancers.

Age Factors↗
PubMed1986

Bloom's syndrome. XIII. DNA-polymerase activity of cultured lymphoblastoid cells.

The biochemical defect in Bloom's syndrome (BS) remains unknown, but two characteristic features of BS cells point to a disturbance of DNA replication, namely, an excessive number of sister-chromatid exchanges (SCEs) in bromodeoxyuridine (BrdU)-substituted cells and an abnormally slow rate of replicon elongation. The hypothesis of an abnormal DNA polymerase as the explanation for these observations was tested using an in situ assay system for DNA polymerase activity and to estimate molecular weights in cellular extracts of cultured BS cells. DNA polymerase subunits in cellular extracts from the BS cells when separated electrophoretically on polyacrylamide gels showed the same mobilities (i.e., molecular weights) as the controls and were equally effective at promoting the incorporation of isotopically labeled nucleosides. It is concluded that the genetic defect in BS has no direct effect on either DNA-polymerase activity or the amounts and molecular weights of the different forms of the enzyme.

Autoradiography↗
PubMed1986

Strong effects of 5-azacytidine on the in vitro lifespan of human diploid fibroblasts.

Azacytidine (5-aza-CR) and azadeoxycytidine (5-aza-CdR) are known to inhibit the methylation of cytosine (5-mC) in DNA, and their effects on the long-term growth of human fibroblasts, strain MRC-5, have been examined. A single treatment with either analogue initially inhibits growth, but the cells recover to normal morphology, growth rate and cell density at confluence. However, a memory of the treatment is retained, since the cells' subsequent lifespan is considerably reduced in comparison with controls, and the terminal stages of growth are indistinguishable from senescent cultures of untreated cells. The effect of 5-aza-CR or 5-aza-CdR does not appear to be closely related to the concentration used, or to the length of treatment up to about half-way through the total lifespan. Sequential doses have cumulative effects on longevity. There is evidence that the pattern of 5-mC in mammalian DNA is inherited via cell division; therefore, a reduction in 5-mC induced by a pulse treatment of 5-aza-CR or 5-aza-CdR will be transmitted to all descendants. The results are consistent with independent observations that the level of 5-mC declines continually during the serial subculture of human diploid cells. The analogues would be expected to precipitate this decline and thereby advance the physiological age of the culture. The results provide support for the view that the random loss of methyl groups in DNA may eventually have deleterious consequences, such as aberrant epigenetic changes in gene expression.

5-Methylcytosine↗
PubMed1986

Congenital absence of the C1 vertebral arch.

Congenital absence of part of the anterior arch of the atlas, a rare disorder, was observed in two patients. The defect in the C1 cervical vertebrae, caused by congenital nonfusion of the arch of C1, may be confused with a cervical spinal fracture on plain radiographs of the cervical spine. The diagnosis is established by characteristic radiological changes, especially in the CT scan and bone scan. Because congenital anomalies of the cervical spine may predispose to instability of the cervical spine and can be confused with traumatic lesions, thorough evaluation is warranted. Treatment should be based on signs of instability, if present.

Adolescent↗
PubMed1986

Azacytidine-induced reactivation of a DNA repair gene in Chinese hamster ovary cells.

Six X-ray-sensitive (xrs) strains of the CHO-K1 cell line were shown to revert at a very high frequency after treatment with 5-azacytidine. This suggested that there was a methylated xrs+ gene in these strains which was structurally intact, but not expressed. The xrs strains did not complement one another, and the locus was autosomally located. In view of the frequency of their isolation and their somewhat different phenotypes, we propose that the xrs strains are mutants derived from an active wild-type gene. However, there is in addition a methylated silent gene present in the genome. Azacytidine treatment reactivated this gene. We present a model for the functional hemizygosity of mammalian cell lines, which is based on the inactivation of genes by de novo hypermethylation. In contrast to results with xrs strains, other repair-defective lines were found not to be reverted by azacytidine.

Animals↗
PubMed1986

Major operative trauma increases peripheral amino acid release during the steady-state infusion of total parenteral nutrition in man.

The effect of major operative trauma on skeletal muscle metabolism was examined in nine patients receiving a constant infusion of calories (1460 kcal/m2/day) and protein (75 gm of amino acids/m2/day) for 5 days before and 4 days after an operation. Compared with the preoperative state, 72 hours after the operation there was a significant rise in arterial levels of glucagon, cortisol, norepinephrine, and inactive triiodothyronine and a drop in concentrations of insulin, active triiodothyronine, and amino acids. Forearm blood flow increased, as well as the efflux from forearm muscle of lactate, taurine, serine, glycine, valine, methionine, isoleucine, leucine, phenylalanine, lysine, arginine, and total amino acid nitrogen (440%). This loss of muscle protein after trauma is associated with increased muscle proteolysis, as measured by increased urinary 3-methylhistidine excretion (83%), and accounts for increased nitrogen loss (54%) from the body. Increased activity of the sympathetic nervous system is manifested by increased levels of epinephrine and norepinephrine, a relative lack of insulin, and increased levels of glucagon. This hormonal milieu plays an important role in the production of hypoaminoacidemia, increased efflux of amino acids and lactate from muscle, and negative nitrogen balance observed in these traumatized patients.

Aged↗
PubMed1986

Gene conversion.

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Biological Evolution↗
PubMed1985

Aspects of DNA repair and nucleotide pool imbalance.

Evidence that optimum repair depends on adequate pools of deoxynucleotide triphosphates (dNTPs) comes from the study of pyrimidine auxotrophs of Ustilago maydis. These strains are sensitive to UV light and X-rays, and for pyr1-1 it has been shown that the intracellular concentration of dTTP is reduced about 7-fold. Evidence has been published that DNA repair synthesis may require higher concentrations of dNTPs, than chromosome replication. The survival curve of pyr1-1 after UV-treatment, and split dose experiments with wild-type cells, provide evidence for an inducible repair mechanism, which probably depends on genetic recombination. Although inducible repair saves cellular resources, it has the disadvantage of becoming ineffective at doses which are high enough to inactivate the repressed structural gene(s) for repair enzymes. To ensure survival it is vital for organisms to preserve the integrity of their DNA, and this is accomplished both by accurate replication and by repair. It is clear that a wide variety of repair mechanisms have evolved to remove lesions which arise either spontaneously (such as the deamination of cytosine to uracil) or as a result of damage from external agents. Nevertheless, it would be incorrect to assume that all species require all possible pathways of repair. It is now well established that the accuracy of DNA and protein synthesis depends on proof-reading or editing mechanisms (for a review, see Ref. 5). These consume energy and may slow down the rate of synthesis, therefore organisms must invest metabolic resources to achieve any given level of accuracy. Optimum accuracy levels will evolve from the balance between error avoidance in macromolecular synthesis and physiological efficiency in growth and propagation [11, 12, 22].(ABSTRACT TRUNCATED AT 250 WORDS)

Basidiomycota↗