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Biomedical subjects

A Rowan

Publications and source records attributed to A Rowan.

32 records · Page 2Linked to original sources
PubMed1994

Beta 2-microglobulin gene mutations: a study of established colorectal cell lines and fresh tumors.

The technique of single-strand conformation polymorphism (SSCP) was used to screen a series of 37 established colorectal cell lines, 22 fresh tumor samples, and 22 normal DNA samples for mutations in the beta 2-microglobulin gene. Exon 1 (including the leader peptide sequence) and exon 2 were screened separately. Six of 37 colorectal cell lines and 1 of 22 fresh tumors were shown to contain mutations, whereas no mutations were detected in the normal DNA samples. Sequencing of these mutations showed that an 8-bp CT repeat in the leader peptide sequence was particularly variable, since 3 of the cell lines and one fresh tumor sample have deletions in this region. In the related cell lines, DLD-1 and HCT-15, two similar mutations were identified, a C-->A substitution in codon 10 and a G-->T mutation in the splice sequence of intron 1. Expression of beta 2-microglobulin was examined using a series of monoclonal antibodies in an ELISA system. Reduced expression correlated with a mutation in one allele of beta 2-microglobulin, whereas loss of expression was seen in instances where a line was homozygous for a mutation or heterozygous for two mutations.

Amino Acid Sequence↗
PubMed1993

Tissue typing the HLA-A locus from genomic DNA by sequence-specific PCR: comparison of HLA genotype and surface expression on colorectal tumor cell lines.

A system devised for tissue typing the HLA-A locus by PCR from genomic DNA has been used to investigate abnormalities of HLA expression in a panel of 30 colorectal tumor cell lines, by comparing the HLA-A locus genotype with surface expression of HLA. Three cell lines showed complete lack of HLA expression associated with failure to express beta 2-microglobulin. In two other cell lines, loss of expression of HLA-A2 was observed, in spite of the presence of the gene in genomic DNA. Eleven cell lines gave a single HLA-A locus specificity on PCR typing. In one of these cell lines we have demonstrated the loss of an HLA-A locus gene in the tumor cell by comparison with DNA from a lymphoblastoid B-cell line derived from the same patient. These data indicate that at least three independent mechanisms were involved in the loss of HLA expression on the colorectal tumor cell lines.

Base Sequence↗
PubMed1993

New vector for transfer of yeast artificial chromosomes to mammalian cells.

A modification vector has been constructed to facilitate the transfer of yeast artificial chromosomes (YACs) to mammalian cells in culture by targeting a dominant selectable marker (G418 resistance) to the right arm of pYAC4 clones. The ADE2 gene is used for yeast selection with consequent disruption of the URA3 gene, allowing direct modification of YACs within the common host strain AB1380, and providing a simple test for correct targeting. This vector has been tested by modification of a 550-kb YAC containing part of the human MHC class II region and transfer to CHO cells by protoplast fusion. Analysis of 15 independent G418-resistant CHO lines obtained following fusion suggests the majority contain a complete YAC with moderate amplification in some lines.

Animals↗
PubMed1993

Loss of human leukocyte antigen expression on colorectal tumor cell lines: implications for anti-tumor immunity and immunotherapy.

A system devised for tissue typing the human leukocyte antigen-A (HLA-A) locus from genomic DNA by the polymerase chain reaction (PCR) has been used to investigate abnormalities of HLA expression in a panel of 30 cell lines derived from colorectal adenocarcinomas, by comparison of the HLA-A locus genotype with surface expression of HLA. Eleven cell lines gave single HLA-A locus specificity on PCR typing, suggesting that loss of HLA alleles is a common abnormality. In one of these cell lines the loss of an HLA-A locus allele was confirmed by comparison with DNA from a lymphoblastoid B cell line derived from the same patient. In three cell lines, loss of expression of an HLA-A locus determinant was observed in spite of the presence of the relevant allele in genomic DNA. Three cell lines showed absent HLA expression associated with failure to express beta 2-microglobulin. These data indicate that at least three independent mechanisms were involved in the loss of HLA expression on the colorectal tumor cell lines.

Antigens, Surface↗
PubMed1991

Pain, suffering, and anxiety in animals and humans.

We attempt to bring the concepts of pain, suffering, and anxiety into sufficient focus to make them serviceable for empirical investigation. The common-sense view that many animals experience these phenomena is supported by empirical and philosophical arguments. We conclude, first, that pain, suffering, and anxiety are different conceptually and as phenomena, and should not be conflated. Second, suffering can be the result--or perhaps take the form--of a variety of states including pain, anxiety, fear, and boredom. Third, pain and nociception are not equivalent and should be carefully distinguished. Fourth, nociception can explain the behavior of insects and perhaps other invertebrates (except possibly the cephalopods). Fifth, a behavioral inhibition system associated with anxiety in humans seems to be present in mammals and most or all other vertebrates. Based on neurochemical and behavioral evidence, it seems parsimonious to claim that these animals are capable of experiencing anxious states.

Animal Welfare↗
PubMed1990

p53 mutations in colorectal cancer.

Immunohistological staining of primary colorectal carcinomas with antibodies specific to p53 demonstrated gross overexpression of the protein in approximately 50% of the malignant tumors examined. Benign adenomas were all negative for p53 overexpression. To determine the molecular basis for this overexpression we examined p53 protein expression in 10 colorectal cancer cell lines. Six of the cell lines expressed high levels of p53 in ELISA, cell-staining, and immunoprecipitation studies. Direct sequencing and chemical-mismatch-cleavage analysis of p53 cDNA by using the polymerase chain reaction in these cell lines showed that all cell lines that expressed high levels of p53 were synthesizing mRNAs that encoded mutant p53 proteins. In two of those four cell lines where p53 expression was lower, point mutations were still detected. Thus, we conclude that overexpression of p53 is synonymous with mutation, but some mutations would not be detected by a simple immunohistochemical analysis. Mutation of the p53 gene is one of the commonest genetic changes in the development of human colorectal cancer.

Adenocarcinoma↗
PubMed1983

Shortcomings of LD50-values and acute toxicity testing in animals.

The author argues that the standard practice of determining an LD50 with 95% confidence limits is a waste of animals since the extra statistical precision is undermined by numerous other factors. For example, the LD50 of a given chemical often varies by at least 10-fold between different animal species and strains. Also, environmental factors can result in substantial differences in the LD50 of a given chemical in a given animal strain. Therefore, the use of this measure as a general index of toxicity, as a guide to further pharmacological or toxicological studies, or as a guide to human toxicity involves unnecessary and needless taking of animal life. These points will be amplified and substantiated by actual examples. Finally, the author will make some suggestions as to what could constitute a satisfactory acute animal test given current scientific and regulatory needs.

Aging↗
PubMed1983

Shortcomings of alternative techniques for the assessment of acute toxicity.

Relatively little work has been done on the development of cell culture and other models to assess the acute toxicity of chemicals. Many of the present shortcomings have already been addressed in earlier presentations but will be summarized by the author. The parameters necessary for an appropriate model of acute toxicity will be discussed and the difference between testing for specific and general effects will be highlighted. Some possible future research directions and research needs will be discussed.

Animals↗