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Biomedical subjects

L Liu

Publications and source records attributed to L Liu.

At least 1,297 records · Page 72Linked to original sources
PubMed1987

Liquid and solid two-phase radioimmunoassay--simultaneous measurement of levels of triiodothyronine and thyroxine of human serum in a single specimen.

The principle of the liquid and solid two-phase radioimmunoassay and its application to measuring the concentrations of triiodothyronine and thyroxine of human serum in a single sample at the same time are described in this paper. Rabbit anti-triiodothyronine antiserum was immobilized on the inner surface of a plastic tube as solid-phase radioimmunoassay system of testing triiodothyronine and donkey anti-rabbit gamma globulin antiserum was used to separate immunocomplex in liquid-phase radioimmunoassay system of thyroxine reaction. In both systems, radioiodine-125-labelled antigens were used as tracer. Through simple calculation, we can get the results of serum concentrations of triiodothyronine and thyroxine in a single sample. Compared with classical single-component radioimmunoassay of triiodothyronine and thyroxine and by methodological appraisal of two-phase radioimmunoassay itself, this method has the advantages of very high efficiency, reliability and also has the same specificity and precision.

Humans↗
PubMed1986

Variable effects of DNA-synthesis inhibitors upon DNA methylation in mammalian cells.

Post-synthetic enzymatic hypermethylation of DNA was induced in hamster fibrosarcoma cells by the DNA synthesis inhibitors cytosine arabinoside, hydroxyurea and aphidicolin. This effect required direct inhibition of DNA polymerase alpha or reduction in deoxynucleotide pools and was not specific to a single cell type. At equivalently reduced levels of DNA synthesis, neither cycloheximide, actinomycin D nor serum deprivation affected DNA methylation in this way. The topoisomerase inhibitors nalidixic acid and novobiocin caused significant hypomethylation indicating that increased 5-mCyt content was not a necessary consequence of DNA synthesis inhibition. The induced hypermethylation occurred predominantly in that fraction of the DNA synthesized in the presence of inhibitor; was stable in the absence of drug; was most prominent in low molecular weight DNA representing sites of initiated but incomplete DNA synthesis; and occurred primarily within CpG dinucleotides, although other dinucleotides were overmethylated as well. Drug-induced CpG hypermethylation may be capable of silencing genes, an effect which may be relevant to the aberrantly expressed genes characteristic of neoplastic cells.

Animals↗
PubMed1986

Inhibition of cell proliferation by cytosine-arabinoside and its interference with spatial and temporal differentiation patterns in the chick retina.

Incubation of chick embryos with 200 nmoles/egg of cytosine arabinoside (AraC) completely inhibits cell proliferation in the embryo. At an age older than embryonic day 4 (E4) more than 90% of the embryos survive this treatment. The drug induces various malformations; in particular the retina is heavily affected. This simple method offers the possibility to study the effect of a more or less decreased cell production on processes of further differentiation and histogenesis of retinal tissue. The following results are obtained: In spite of the inhibition of cell proliferation in the retina by AraC an abnormally thick basal lamina is found and the expansion of the eye still proceeds, indicating that eye growth is not only dependent on retinal cell numbers. Stereotyped malformations of retinal histogenesis are induced and categorized into three groups: in addition to areas of normal structure cells are found arranged in rosettes and in half-rosettes sometimes linked by areas of undefined transient cell arrangements. The results point to a strong tendency of a severely diminished cell population to form regularly laminated retinal-like structures as long as a minimal ratio of cell types is given. The spatio-temporal appearance of the type of retinal malformation in a given retinal area is dependent on the time of AraC exposure and thus on the degree of differentiation reached at a "spatio-temporal spot": Full rosettes develop at earlier, and half-rosettes at later stages of AraC interference. Furthermore, deformities first appear on temporal and ventral sides. Thus, the establishment of these malformations follows and reflects the normal sequence of differentiation within the retina. Cells within rosettes organize in specific layers and start to differentiate normally. This shows that earlier formed cells are not dependent on the influence of factors derived from cells that are formed later for their proper differentiation.

Animals↗
PubMed1986

Characterization of myogenic cell lines derived by 5-azacytidine treatment.

Three myogenic clonal cell lines were isolated from C3H 10T1/2 C18 cells (10T1/2) treated with 5-azacytidine (5-aza-CR). These lines reproducibly underwent fusion at confluence into functional myotubes capable of contracting in response to acetylcholine. The degree of fusion could be increased two- to threefold if the cells were grown on gelatin-coated dishes. All of the cell lines lost some of their myogenic potential after repeated passaging and the percentage of colonies capable of forming muscle was not increased by permissive media containing 2% horse serum. The 10T1/2 cells expressed only the BB form of creatine phosphokinase but all of the myogenic clones expressed additionally the MM and MB forms of the isozyme after fusion. The overall genomic level of 5-methylcytosine was decreased in some but not all of the cell clones tested. Comparisons between the 10T1/2 cells which never form muscle without 5-aza-CR treatment and clonal derivatives of committed cell types might be of value in understanding the molecular basis of the commitment process.

Animals↗
PubMed1986

Interferon inhibits the growth of Legionella micdadei in mouse L cells.

The intracellular growth of Legionella micdadei was inhibited in mouse L cells treated with interferon (IFN). This IFN-mediated restriction was dose-dependent and required preincubation of the L cells with high doses of IFN (1,000 U/ml) for maximal inhibition. Incubation of L. micdadei with IFN alone had no detectable effect on growth of the bacteria. The IFN-mediated growth restriction was not dependent upon tryptophan concentration in the culture medium.

Animals↗