Biomedical subjects
Publications and source records attributed to G T Lee.
Leukemia is the major form of cancer in children in Britain and mirrors the percentage of children affected in the USA. This report outlines some of the medical aspects of leukemia and its treatment and gives a guide to the dentist, who may have the responsibility of dealing with leukemic children and their families.
The objective of the study was to determine quantitatively the effect on the potential for in situ remineralization of artificial caries-like lesions in human enamel when sugar-free gum containing mainly sorbitol as sweetener was chewed after meals and snacks. Artificial white-spot lesions were created in extracted human premolars and divided into three parts. One part was used as reference and the other two worn consecutively for two 21-day periods by 10 volunteers in a cast silver band cemented on lower molar teeth and covered with gauze to promote plaque formation. During the experimental periods, the subjects used fluoridated toothpaste twice daily, and consumed three meals (breakfast, lunch, and dinner) and two snacks (selected from chocolate bar, raisins, chocolate wafer, and iced cupcake). Sorbitol gum was chewed for 20 min immediately after each meal or snack during one of the experimental periods. The three parts of the enamel lesions were then sectioned (congruent to 80 microns) and examined together by means of quantitative microradiography and by polarized light microscopy. All estimates of mineral content indicated that significant remineralization occurred and was approximately doubled with gum-chewing. It is suggested that sorbitol gum stimulates salivation, which is responsible for the significantly enhanced remineralization, thus contributing to a therapeutic, caries-preventive effect. Because the gum was chewed immediately after meals and snacks, inhibition of demineralization may also have occurred.
This study examines the pattern of behavior of children referred to the Liverpool Dental Hospital for previous lack of cooperation during dental treatment. During a normal treatment session a proportion of these patients refused to allow treatment to proceed. Comparisons were made of the behavioral profiles obtained from detailed observation of treatment by videotape recordings between children who refused or accepted treatment with a comparison group of children. Refusers were characterized by behavior, which prevented treatment from continuing, e.g., closing their mouths and by weeping. Increased levels of restlessness and verbal complaints were not found in the refusers compared with the other children who received treatment.
The murine monoclonal antibody CI-panHu reacts strongly with the cell surface of all human cells, including erythrocytes, tumour cells and HLA-A,B,C-negative cell lines. As such, this antibody defines the first pan-human cell-surface antigen reported. The antigenic determinant detected is associated with a protein doublet of 16,000 MW whose expression is restricted to cells from humans, apes and some species of Old World monkeys. Antibody reactivity is not diminished by routine fixation procedures, nor by paraffin-embedding, and the antigenic determinant is relatively protease-resistant. The use of this antibody as a positive control in immunoassays of human cells is discussed.
We constructed insertion mutants of herpes simplex virus type 1 that contained a duplication of DNA sequences from the BamHI-L fragment (map units 0.706 to 0.744), which is located in the unique region of the L component (UL) of the herpes simplex virus type 1 genome. The second copy of the BamHI-L sequence was inserted in inverted orientation into the viral thymidine kinase gene (map units 0.30 to 0.32), also located within UL. A significant fraction of the progeny produced by these insertion mutants had genomes with rearranged DNA sequences, presumably resulting from intramolecular or intermolecular recombination between the BamHI-L sequences at the two different genomic locations. The rearranged genomes either had an inversion of the DNA sequence flanked by the duplication or were recombinant molecules in which different regions of the genome had been duplicated and deleted. Genomic rearrangements similar to those described here have been reported previously but only for herpes simplex virus insertion mutants containing an extra copy of the repetitive a sequence. Such rearrangements have not been reported for insertion mutants that contain duplications of herpes simplex virus DNA sequences from largely unique regions of the genome. The implications of these results are discussed.
Previous studies [W. T. Ruyechan, L. S. Morse, D. M. Knipe, and B. Roizman (1979) J. Virol. 29, 677-697] have shown that multiple mutations are responsible for the mutant phenotypes of herpes simplex virus type 1, strain MP, and have indicated that these mutations may be located on the genome between map coordinates 0.70 and 0.83. Strain MP produces large syncytial (Syn) plaques on many cell types and does not express glycoprotein C (gC-), whereas a sibling strain mP produces wild-type, small, nonsyncytial (Syn+) plaques and is gC+. Cloned DNA fragments from strains MP and mP (and strain F) were used in marker transfer and marker rescue experiments to map more precisely the mutations in MP. It was found that a 680-bp fragment from MP DNA (map coordinates 0.735 to 0.740) could transfer a Syn marker to mP and that, conversely, an overlapping fragment from mP DNA (map coordinates 0.728 to 0.744) could rescue the Syn mutation of MP. Recombinant viruses obtained in these experiments differed from the donor of the cloned DNA fragment in plaque size, however, indicating that mutation(s) at other regions of the MP genome cause enlarged plaques, in which the infected cells are less rounded than in wild-type plaques. A fragment of MP DNA from map coordinates 0.60 to 0.64 transferred a mutation causing the gC- phenotype to strain mP, and a fragment of F DNA from map coordinates 0.62 to 0.64 rescued the gC- mutation of MP. These results, coupled with data published by Frink et al. [(1983) J. Virol. 45, 643-467], indicate that the mutation responsible for the gC- phenotype of MP may be in the structural gene for gC.
The basis for the inability of the macroplaque (MP) strain of herpes simplex virus type 1 to express mature glycoprotein C (gC) was examined. RNA transfer (Northern) blot analysis with hybridization probes from the region of the herpes simplex virus type 1 DNA known to encode the gC gene indicated that gC mRNA was produced in MP-infected HeLa cells at levels relative to other mRNAs comparable with that seen in KOS-infected cells. Comparative nucleotide sequence analysis of the gC gene from the MP and KOS strains, coupled with the results of recently reported marker rescue experiments, indicates that the inability of MP to produce gC is due to a frameshift mutation in the gC-coding sequence. Because two different (out-of-phase) open reading frames overlap the gC-coding sequence in the region of the mutation, MP mRNA can encode two gC-related polypeptides. Two polypeptides of the predicted size and precipitable by anti-gC antibodies were produced by in vitro translation of MP mRNA. These polypeptides have not been detected in extracts from infected cells with the same antibodies. Comparative nucleotide sequence analyses led to several corrections in the published sequence for the gC gene and the 17,800-molecular-weight polypeptide gene just to the right in KOS DNA. These relatively minor effects on the predicted amino code sequence of gC are tabulated.
Monoclonal antibodies directed against glycoprotein D of herpes simplex virus completely inhibited fusion of Vero cells infected with type 1 virus. In contrast, several monoclonal antibodies directed against other viral glycoproteins, including B, were ineffective or were only minimally inhibitory at the highest concentrations tested.
Previous reports have described mutants of herpes simplex virus type 1 that fail to produce or accumulate one of the major glycoproteins, glycoprotein C (gC). This defect is not lethal in cell culture, has been associated with the syncytial plaque morphology of some mutants, and may result from mutations that map to a region on the genome noncontiguous with the structural gene for gC. To investigate the conditions required for, and consequences of, gC expression in a specific genetic background, we have inserted a wild-type allele of the gC gene into the thymidine kinase gene (tk) of a gC- fusion-inducing viral mutant, strain MP. This was accomplished by identifying cloned viral DNA fragments homologous to gC mRNA, inserting the appropriate fragments into the viral tk cloned in pBR322, and then cotransfecting cells with the recombinant plasmids and DNA from strain MP, for selection of insertional TK- mutants. All TK- mutants containing insertions of appropriate sequences (in either orientation) into tk were found to express gC while maintaining the syncytial plaque morphology of strain MP. Elimination of the insertion from one of the TK- mutants was accompanied by loss of ability to produce gC. Our results permit more precise mapping of the DNA sequence encoding gC, to a subfragment of Sal I fragment R (map coordinates 0.620-0.640) and indicate also that promoter sequences for the gC gene may be located in this fragment. Moreover, we can conclude that the previously described regulatory mutation of strain MP does not prevent expression of gC from the DNA inserted into its gene tk and that the syncytial phenotype of MP cannot be due solely to absence of gC.
To map the structural genes for the gD and gE polypeptides and for other viral products encoded in the S component of herpes simplex virus type 1 DNA, we selected mRNAs capable of hybridizing to cloned viral DNA fragments and translated the mRNAs in vitro to determine which polypeptides were encoded therein. The gD and gE polypeptides were identified by immunoprecipitation with appropriate monoclonal and monospecific antibodies, whereas the other polypeptides were characterized only by their electrophoretic mobilities in polyacrylamide gels. We found that gD mRNA hybridized to a single SacI subfragment of BamHI fragment J, whereas gE mRNA hybridized to an adjacent SacI subfragment of BamHI fragment J and also to BamHI fragment X. These and other results permit the conclusion that the structural gene for gD is located between map coordinates 0.911 and 0.924, and the gene for gE is between map coordinates 0.924 and 0.951. We also found that mRNAs for polypeptides of 55,000, 42,000, 33,000, and 22,000 molecular weight hybridized to DNA fragments spanning the regions from map coordinates 0.911 to 0.924, 0.897 to 0.911, 0.939 to 0.965, and 0.939 to 0.965, respectively. Finally, in accord with the results of others, we found that mRNA for a 68,000-molecular-weight polypeptide hybridized to the two noncontiguous BamHI fragments N and Z, which share a reiterated DNA sequence.
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Peptide production in senescent and presenescent human foreskin fibroblasts was measured using 2-dimensional polyacrylamide gel electrophoresis. This procedure permits the visualization of a cohort of the major peptides being produced. Among this cohort of over 500 peptides only two were found to differ in relative amount in that more was being produced in senescent cells. This difference was confirmed by measurements of the relative intensity of the peptide spot. This difference was senescent cell-specific and not due to the differences in rate of growth of senescent and non-senescent cells.
Patterns of newly synthesized proteins of Vero cells in different growth states were obtained using two-dimensional gel electrophoresis. The 240 most prevalent peptide spots were then compared. Cells in exponential growth and in the stationary phase were found to have patterns of peptide spots characteristic of their state of growth. The transition between these patterns is progressive, and the cells acquire a pattern characteristic of quiescent cells by the late exponential phase. These observations suggest that a series of modulations in gene expression occurs during the transition of growth states in animal cells that leads to the specific appearance or disappearance of certain cellular peptides.
Monkey fibroblasts maintained in culture regulate their levels of intracellular protein throughout the growth cycle by means of variations in the rate of protein biosynthesis. Cytoplasmic mRNA in stationary phase cells was compared to that in exponential phase cells. In stationary phase cells 56% of the cytoplasmic polyadenylated RNA was found in the 40--90S postpolysomal region of sucrose sedimentation gradients, while only 23% was found in this region in exponential phase cells. Analysis of electron micrographs of sectioned exponential and stationary phase cells revealed that this shift in polyadenylated RNA location is accompanied by a loss of polysome-like aggregates of ribosomes. Most if not all of this species of postpolysomal polyadenylated RNA is not being translated by single ribosomes since no detectable amounts of nascent peptide were present in this region. This nonpolysomal polyadenylated RNA is comparable in size to polysomal polyadenylated RNA. The length of the 3'-poly(A) tract was also comparable for these two species. The extent of capping of poly(A)-containing molecules was also comparable for these two species. The template activity of nonpolysomal RNA in a wheat germ extract was comparable to that of polysomal RNA. The peptides produced by these two preparations were of a similar large size. Furthermore, most of the nonpolysomal polyadenylated RNA of stationary phase cells was driven into polysomes in the presence of a low dose of cycloheximide. Therefore, we conclude that the untranslated mRNA that accumulates in stationary phase cells is structurally intact, is fully capable of being translated, and is not being translated due to the operation of a translational initiation block.
Protein synthesis and degradation were studied throughout a growth cycle of Vero cells. The rate of protein synthesis, measured as the rate of amino acid incorporation, reached a maximum at the mid-exponential phase and declined to 10-30% of the maximum in the stationary phase. The rate of protein degradation, measured as the release of radioactive amino acids from uniformly labelled cellular proteins, did not vary in the growth cycle. The amount of protein per cell, measured by an isotopic method, remained constant when normalized to account for the variation in the proportion of actively dividing cells in the cell population during the growth cycle. Cellular protein was determined using this method since it was found that the chemical determination of the amount of protein in the monolayer was not accurate during the early stage of the growth cycle. This was due to a significant amount of serum protein adsorbed to the cells. In this study we were able to show that, in Vero cells, protein synthetic activity is correlated with the rate of cell division, and variations in the rate of synthesis alone are sufficient to meet the changing requirements for cellular protein in a growth cycle.
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