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Biomedical subjects

O Heby

Publications and source records attributed to O Heby.

At least 73 records · Page 4Linked to original sources
PubMed1984

Localization of ornithine decarboxylase in mutant CHO cells that overproduce the enzyme. Differences between the intracellular distribution of monospecific ornithine decarboxylase antibodies and radiolabeled alpha-difluoromethylornithine.

The intracellular localization of ornithine decarboxylase (ODC), a key enzyme in polyamine synthesis and cell growth, is a matter of present debate. Using two independent methods of analysis, we have attempted to determine the actual distribution of ODC in a mammalian cell. To overcome the problem of a normally very low cellular ODC content, we have used ODC overproducing mutant CHO cells. These mutant cells exhibit a 10-fold higher ODC activity than do the wild type cells. The localization of ODC protein in exponentially growing cells, was determined by indirect immunofluorescence microscopy (permeabilized whole-cell preparations and 1 micron sections), using a monospecific ODC antibody. The intracellular localization of catalytically active ODC was determined by light and electron microscope autoradiography following pulselabeling of cells with alpha-difluoromethyl(5-3H)ornithine (3H-DFMO) at the time of peak ODC activity. alpha-Difluoromethylornithine (DFMO) is an enzyme-activated irreversible inhibitor of ODC and binds covalently to the active enzyme. The specificity of this reaction in the cell was ascertained by immunoprecipitation of 3H-DFMO-labeled ODC. ODC (as determined by both methods) was present in all the cells of a serum-stimulated monolayer culture. The highest concentration of ODC protein and of catalytically active ODC was observed in the smallest and most rapidly proliferating cells. Polyploid and multinuclear cells always exhibited the lowest concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Polyamines in early embryonic development: their relationship to nuclear multiplication rate, cell cycle traverse, and nucleolar formation in a dipteran egg.

Polyamine synthesis and accumulation were assessed from fertilization until gastrulation in a dipteran egg (Calliphora erythrocephala Meigen). Spermidine synthesis was activated immediately after fertilization, generating a broad spermidine peak during early cleavage. This period is characterized by the most rapid nuclear multiplication known from animal material. Cleavage consists of nuclear multiplication only, and the egg remains syncytial until gastrulation. After nine synchronous nuclear divisions with a cycle length of 10 min, the cycle length is gradually increased to 20 min during the subsequent four parasynchronous nuclear divisions. The spermidine level decreased in parallel with this decreasing rate of nuclear division. The interphase of the next nuclear cycle is remarkably prolonged and lasts for more than 90 min, i.e., until after the onset of gastrulation. It consists of an initial short S phase followed by a longer G2 phase; G1 is extremely short or absent. During this prolonged interphase, spermidine content showed a biphasic pattern of changes with peaks during S and late G2. The S-phase peak also coincides with the first appearance of nucleoli during embryogenesis. The late-G2-phase peak coincides with the period of rapid cytokinesis, during which all nuclei in the peripheral layer of the syncytium become separated by membranes forming a cellular blastoderm. The polyamine pattern is consistent with the idea that the polyamines play an important role in DNA replication and in cytokinesis as well as in nucleolar formation.

Animals↗
PubMed1983

Urinary polyamine excretion as related to cell death and cell proliferation induced by carbon tetrachloride intoxication.

This study addresses the question whether urinary polyamine excretion is related to cell death or cell proliferation. CCl4 intoxication of the rat was used as the experimental model. Treatment with CCl4, a hepatotoxic haloalkane, produces an initial phase of liver cell death succeeded by a regenerative phase of growth, during which the liver is restored. The highest rate of putrescine (and spermidine) excretion occurred during the first 24 hr of CCl4 intoxication and coincided with the period of maximum liver damage. During subsequent liver regeneration the rate of excretion of both polyamines decreased.

Animals↗
PubMed1983

Suppression of ribosomal gene expression in oocytes and nurse cells of a polychaete as a result of polyamine synthesis inhibition.

The role of the polyamines in ribosomal gene expression was evaluated in the polychaete Ophryotrocha labronica by analyzing the effects of polyamine synthesis inhibition on RNA synthesis during oogenesis, a period characterized by intense nucleolar activity. At various stages of oogenesis adult polychaete females were blocked in their polyamine synthesis by the addition of 10 mM DL-alpha-difluoromethylornithine (DFMO) to the sea water in which they were cultivated. To monitor RNA synthesis during DFMO treatment the animals were pulse-labeled with [5-3H]uridine and processed for autoradiography. Light and electron microscope autoradiographs demonstrate that DFMO treatment suppresses incorporation of label into nucleolar RNA (rRNA) both in the oocytes and their associated nurse cells. The ultrastructural appearance of both cell types reveals interference with nucleolar and ribosomal activity; the endoplasmic reticulum is deprived of ribosomes, and the production of protein granules (vitellogenesis) is reduced. The high specificity of DFMO for polyamine synthesis and the fact that the effects of DFMO were counteracted by addition of a low concentration (10 microM) of putrescine shows that the observed interference with ribosomal gene expression is indeed due to polyamine deficiency.

Age Factors↗
PubMed1983

Effects of polyamine limitation on nucleolar development and morphology in early chick embryos.

Inhibition of polyamine synthesis in early chick embryos by in ovo treatment with DL-alpha-difluoromethylornithine (DFMO), injected beneath the blastoderm after 5 h of incubation, permanently blocks post-gastrular development. After the first day of polyamine limitation, the embryos possess a thickened primitive streak. Further morphogenesis is blocked and the ectoderm and mesoderm are condensed around the streak. There is obvious suppression of nucleolar formation in 24 h DFMO-treated embryos. In the mesoderm obliquely in front of Hensen's node the frequency of nucleolus-possessing cells is only a few percent lower in DFMO-treated than in control embryos. However, in the same area the frequency of mesoderm cells possessing multiple nucleoli is about 50% lower in the polyamine-depleted embryos. At the ultrastructural level, mesoderm cells from 24 h DFMO-treated embryos show a reduction of the fibrillar component of the nucleolus with a resulting segregation of the nucleolar material. Our data indicate that stimulation of polyamine synthesis is an obligatory step in the differentiation of epiblast cells into mesoderm cells.

Animals↗
PubMed1983

Nuclear ornithine decarboxylase. Electron microscope autoradiographic identification of the active enzyme using alpha-[5-3H]difluoromethylornithine.

alpha-Difluoromethylornithine (DFMO) is an enzyme-activated irreversible inhibitor of ornithine decarboxylase, that forms a covalent bond with the active enzyme. The highly selective binding of tritium-labeled DFMO to ornithine decarboxylase in vivo, as identified by electron microscope autoradiography, was used to determine the intracellular distribution of the enzyme in the germ cells of a polychaete (Ophryotrocha labronica). In mid-oogenesis ornithine decarboxylase was predominantly located in the nurse cells, which are actively supporting growth of the oocytes. On the basis of biochemical analyses ornithine decarboxylase has been considered mainly cytoplasmic in its distribution. However, in metabolically active polychaete cells (oocytes, nurse cells, intestinal and body wall cells), binding sites for tritiated DMFO, indicating the presence of active ornithine decarboxylase, were as abundant in the nucleus. The nucleolus was the most densely labeled organelle in nurse cells and oocytes.

Animals↗
PubMed1981

Urinary polyamine excretion during growth and regression of 1,12-dimethylbenz[a]anthracene-induced rat mammary carcinoma.

The correlation of urinary excretion of polyamines and tumor mass was examined with the use of a controlled experimental model. Mammary carcinoma growth was induced in Sprague-Dawley virgin rats by intragastric administration of 7,12-dimethylbenz[a]anthracene. Tumors were palpable after about 45 days. After a period of growth, regression of the estrogen-dependent tumors was induced by bilateral ovariectomy. Tumor volume and 24-hour urinary excretion of polyamines were measured during the course of tumor growth and regression. Urinary polyamines were analyzed after acid hydrolysis to determine the total amount of bound and free polyamines. Putrescine excretion followed closely the changes in tumor volume during the course of tumor growth and regression. Urinary spermidine excretion, however, remained essentially unchanged in ovariectomized rats; spermine was barely detectable in any of the urines. There was a high positive correlation between the 24-hour urinary putrescine excretion and urine volume. In nonovariectomized rats, the mammary tumor(s) continued to grow. An unexpected result of the advanced tumor progression was that urinary excretion of both putrescine and spermidine decreased steadily with time as did urine volume. This phenomenon may be due to the fact that complex disturbances of the host metabolism, manifested in decreasing body weight.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1981

Role of the polyamines in germ cell differentiation and in early embryonic development.

The physiological function of the polyamines in germ cell differentiation and in early embryonic development was studied with the aid of the highly specific polyamine synthesis inhibitors DL-alpha-methylornithine (MO) and DL-alpha-difluoromethylornithine (DFMO). In the invertebrate Ophryotrocha labronica DFMO-induced polyamine deficiency severely affected nucleolar formation and activity in germ cell differentiation as revealed by RNA-labelling experiments and by ultrastructural analysis. Both in an invertebrate (Ophryotrocha labronica) and in a vertebrate (chick), inhibitor-induced polyamine deficiency caused a block of embryonic development at gastrulation. The major ultrastructural effect observed in the arrested embryos was an interference with nucleolar formation. Our data suggest that polyamine synthesis is essential for the ribosomal gene expression that is associated with oogenesis and embryogenesis.

Animals↗
PubMed1980

Cytocidal effect of alpha-methylornithine, a competitive inhibitor of ornithine decarboxylase, on ehrlich ascites tumor cells in vivo.

The antiproliferative effect of alpha-methylornithine, an inhibitor of the initial and rate-limiting step in polyamine biosynthesis, was studied on Ehrlich ascites tumor cells grown in vivo. To assess drug-induced cell lethality, the loss of 125I from mice harboring 5-[125I] iodo-2'-deoxyuridine-labeled mouse tumor cells was determined during the course of alpha-methylornithine treatment. Mice that received the drug showed a significant increase in their rate of 125I excretion as compared to controls. This suggests that alpha-methylornithine kills an additional fraction of tumor cells beyond the fraction normally dying.

Animals↗