Cytological,radioautographic and ultrastructural studies on the effect of 5-fluorouracil on rat liver

Summary Young rats were given two doses of 50 mg 5-fluorouracil with a 22-hour interval. One hour after the second dose they were given either cytidine-³H or leucine-³H and killed three hours later. Radioautographs of the livers revealed a decrease in RNA labelling, whereas the protein labelling was essentially uninfluenced. The liver cells exhibited an increase in nucleolar volume. Electron microscopy revealed changes in the ultrastructure of the liver cell nucleoli, while other parts of the cells were essentially unaltered.The investigation was supported by a research grant (project No Y 515) from the Swedish Medical Research Council and Riksföreningen mot Cancer.     

Radioautographic,ultrastructural and biochemical studies on the effect of fluorouracil on the RNA synthesis in the liver of rats

Summary The effects of fluorouracil and uracil on the ultrastructure and RNA synthesis in the liver of rats have been studied. High doses of uracil, contrary to fluorouracil, had no effects on nucleolar ultrastructure. Fluorouracil, even in low doses, depressed the RNA synthesis as studied after cytidine-³H administration. In the radioautographs the depression was especially seen to affect the cytoplasmic labelling. The biochemical analysis showed signs of a depression of ribosomal RNA synthesis and a block or delay in the maturation of ribosomal RNA. Repeated, high doses of uracil also depressed the RNA synthesis but there did not seem to be any delay in the maturation of ribosomal RNA. The results suggest that fluorouracil may affect the RNA metabolism in the nucleoli.The investigation was supported by grants from the Swedish Medical Research Council (Project K 67–12 X-623-03), the Swedish Cancer Society (Project 67:31) and the Medical Faculty of Uppsala.     

Radioautographic studies with methionine-3H and cytidine-3H in protein-fed,protein-deprived and starved rats

Summary Male, growing rats were either fed on a protein-rich or a protein-free diet or starved. At various intervals before they were killed, they were given either cytidine-³H or methionine-³H subcutaneously. Radioautographs of several organs were prepared. Grain counts were performed on sections of liver, pancreas, kidney, adrenal, spleen, stomach, duodenum, heart, lung, striated muscle, testis, skin and cerebellum. They revealed inter alia an increased labelling, especially of ribose nucleic acid, in the liver during protein depletion and starvation. These changes were also found in the ribose nucleic acid labelling of nucleoli, nucleolus-associated chromatin and non-nucleolar nucleus in liver cell nuclei. Changes were also found in many other organs. The findings might be interpreted as signs of a shift of nucleic acid and protein synthesis during protein deprivation and starvation from less essential to more essential' organs. — Some aspects of the intracellular ribose nucleic acid and protein metabolism are discussed.The investigation was supported by a grant from the Swedish Medical Research Foundation.     

Electron-microscopic study on liver cells of rats treated with actinomycin D

Summary Actinomycin D was administered to rats. The animals were also given either cytidine-³H or leucine-³H. Light microscopic radioautography revealed decreased labelling of nucleolar and cytoplasmic RNA and, after high doses, also of chromatin RNA. The protein labelling was not diminished, except perhaps in the nucleoli. Electron-microscopic investigations revealed pronounced changes in the nucleoli, which became compact. Discrete changes were sometimes seen in other parts of the nuclei.The investigation was supported by a research grant (project No. W 337) from the Swedish Medical Research Council.     

The effects of fluorouracil and actinomycin,single and combined,on the nucleolar ultrastructure of various tissues of the rat

Summary 5-fluorouracil and actinomycin D were given, single and combined, to rats. The nucleolar ultrastructure was examined in liver, pancreas, spleen, kidney cortex, adrenal cortex, in epithelial and smooth muscle cells of the small intestine and in the Purkinje cells of the cerebellum. 5-fluorouracil, given alone, provoked changes in all tissues examined. Actinomycin D, given alone, gave changes in all tissues examined, except the cerebellum. Treatment with fluorouracil prior to actinomycin delayed and modified the effect of the latter drug in all tissues examined.This work was supported by grants from the Swedish Medical Research Council (Project K68-12X-623-05) and the Swedish Cancer Society (Project 6831).The results were briefly presented at the XIIth International Congress of Cell Biology, Bruxelles 1968.     

Intranuclear differences in the response of Purkinje cell DNA of the rat cerebellum to bleomycin

Summary A single dose of the DNA-binding cytostatic agent bleomycin (100 g/g body weight, subcutaneously) was given to 10-day-old rats to study unscheduled repair DNA synthesis in nucleolar and in bulk nuclear chromatin of postmitotic Purkinje neurons. The Feulgen reaction and Hoechst 33342 staining were used for quantitative evaluation of nuclear DNA content and chromatin structure. The repair synthesis of DNA was detected by ³H-thymidine autoradiography.The data showed a lesser staining of Purkinje as well as granule cell DNA by Hoechst 33342 in bleomycin-treated animals than in controls, but there was no difference in staining with the Feulgen reation. The mechanisms of DNA staining by both cytochemical methods suggest that bleomycin reacted preferentially with AT-rich and single stranded DNA in cerebellar cells in vivo. Weak ³H-thymidine labelling was found in Purkinje cells of both control and treated rats, but in the latter group the labelling was more pronounced near or over the nucleolus. The enhanced unscheduled DNA synthesis in the nucleolar region of Purkinje cells of treated animals may be due to greater damage of DNA in this region or may indicate a greater ability of the nucleolar chromatin to repair its DNA.Dedicated to Professor Dr. Z. Lojda, Dr. Sc., on the occasion of his 60th birthday.     

Effects of actinomycin D on ribosomal RNA and protein synthesis as revealed by high resolution autoradiography.

Incorporation of tritiated amino acids and uridine was studied in untreated and actinomycin D treated HeLa cells by high resolution autoradiography. Results showed a non-selective inhibition of protein synthesis by actinomycin, as measured by the decrease in radioactive amino acid uptake. When cells pretreated with actinomycin D were incubated with radioactive amino acids and uridine, amino acid uptake in the nucleolus still occurred, while uridine uptake was almost completely eliminated. These findings suggest that in the absence of ribosomal RNA precursor synthesis, nucleolar protein synthesis continues to some extent, and that this protein is transported to the nucleolus.     

REFORMATION OF NUCLEOLI AFTER ETHIONE-INDUCED FRAGMENTATION IN THE ABSENCE OF SIGNIFICANT PROTEIN SYNTHESIS

The rat liver nucleolus, after fragmentation induced by ethionine treatment, has been found to undergo complete reformation by adenine in the presence of a dose of cycloheximide sufficient to cause inhibition of protein synthesis by 90–95%. In contrast, actinomycin D given along with adenine was followed by the appearance of a small compact mass containing only the fibrillar component with no evident granules. This structure resembled pseudonucleoli seen in the anucleolate mutant of Xenopus laevis or in certain early stages of amphibian oocytes. Actinomycin D administered 2 hr after adenine induced a segregation of the fibrillar and granular components of nucleoli similar to that induced in the normal nucleolus. The implications of these findings in relation to nucleolar organization are briefly discussed.     

Silver staining of the nucleolus organizer regions in the interphase cells of an embryonic pig kidney culture during and after administration actinomycin D

Silver staining of nucleolus organizer regions was used for studying their structural alterations during inhibition of ribosomal RNA synthesis by actinomycin D and after its removal in pig kidney cells. Three nuclear types were revealed from the pattern of restored silver grains distribution in the nuclei. When the inhibitor was removed, nuclear multitype gradually disappeared for 24 hours and nuclear RNA synthesis became normal.     

Effect of antibiotics on ribosomal RNA and proteins from Streptococcus pyogenes

Summary Cells of Streptococcus pyogenes were prepared under rigid conditions. The microorganisms were then incubated for 3 hours in the presence or absence of chloramphenicol, actinomycin or puromycin. RNA, ribosomal fraction and ribosomal proteins were isolated from the cells. The materials were invesigated with the help of infra red spectroscopy using the potassium bromide pellet method. Quantitative differences in the 1750–1500 cm^-1 region were observed with materials treated with the antibiotics. Synthetic mixtures of ribosomal RNA with progressively larger amounts of ribosomal proteins show analogous changes, namely a progressive increase in the strength of the 1650 cm^-1 band relative to the 1685 cm^-1 band, and an increase in the 1535 cm^-1 band. The analytical results obtained with the ribosomal RNA isolated from S. pyogenes treated with antibiotics indicated increased amounts of proteins which could not be removed by the applied extraction method. The evidence presented suggests a change in the binding between ribosomal RNA and ribosomal proteins in the material isolated from the antibiotic treated microorganisms. The I. R. spectroscopy seems to be an useful tool in the investigation of some aspects of biological materials.     

Effect of cordycepin (3′-desoxyadenosine) on polytene chromosomes of Chironomus pallidivittatus salivary glands

Incubation of Chironomus pallidivittatus salivary glands in the presence of cordycepin induces the collapse of Balbiani rings. In spite of the great reduction of the Balbiani ring size, ³H-uridine incorporation takes place in these structures and also in puffs and nucleolus. Modifications in the nucleolar pattern of labelling have been observed. Differences were found between the effect of cordycepin and those of actinomycin and adenosine both of which induce the collapse of Balbiani rings.     

The polysomal proteins of L cells. Discrimination between the structural ribosomal proteins, the exchangeable ribosomal proteins and the non-ribosomal proteins by two-dimensional dodecylsulfate electrophoresis and autoradiography.

Three groups of proteins can be clearly discriminated in the total protein of L cell polysomes by selective labelling in the presence of low doses of actinomycin D and two-dimensional polyacrylamide/dodecylsulfate gel electrophoresis followed by autoradiography: (a) structural ribosomal proteins which are not labelled in the presence of actinomycin D and form stained non-radioactive spot in gels; (b) exchangeable ribosomal proteins which are labelled in the presence of actinomycin D and stained radioactive spots; (c) non-ribosomal proteins which are detectable only by autoradiography of gels. The large and small subunits of L cell ribosomes contain respectively 45 and 34 ribosomal proteins with molecular weights less than or equal to 50 000; seven of the large subunit proteins and nine of the small subunit proteins are exchangeable. Most of the non-ribosomal proteins migrate in the region of the related to the separation of the ribosomal proteins of mammalian cells and the possible significance of the presence of non-ribosomal proteins in polysomes are discussed.     

Synthesis of leucine enkephalin derivatives: structure-function studies

Nucleoli isolated from livers of rats injected intraperitoneally with one dose of thioacetamide had a five-fold increase in the rate of RNA synthesis $\text{in vitro}$ when compared with livers of rats treated with saline or CCl₄. The stimulation was maximal 24 hours after treatment and decreased to control values 73 hours after treatment. The enhanced level of nucleolar activity was maintained at that level when thioacetamide was injected daily. Along with the increase in the endogenous activity there was a 7-fold increase in the “free” RNA polymerase I activity determined by blocking the bound enzyme with actinomycin D (7). The nucleoli of the thioacetamide-treated rats offer a useful model of modulation of ribosomal gene function.     

Lymphoblast transformation following adjuvant treatment of an induced colonic cancer with levamisole and fluorouracil

Summary Lymphoblast transformation (LT) in response to phytohaemagglutinin was measured following surgery in a dimethylhydrazine-induced colorectal tumour model in rats. Groups of normal rats were treated with levamisole (given either before and after surgery or only after surgery), fluorouracil (given after surgery), or a combination of both drugs (given either both together or with the administration of levamisole delayed 1 day after fluorouracil). A further untreated group acted as controls and the study was repeated with animals with colonic cancer.The administration of levamisole before surgery increased the restorative effect of postoperative levamisole. The effect was negated by fluorouracil given with levamisole, but not when levamisole was given 1 day after fluorouracil.     

EFFECT OF TEMPERATURE OF ALDEHYDE FIXATION ON THE RADIOAUTOGRAPHIC LOCALIZATION OF RIBONUCLEOPROTEIN IN NUCLEOLI OF HELA CELLS : Inhibition by Puromycin and Actinomycin D

In efforts to clarify the role of the nucleolus and substructures thereof in the assembly or synthesis of protein associated with formation of the complete ribosome, the effect of variation of some conditions of aldehyde fixation on the intranuclear distribution of lysine-³H, arginine-³H, and uridine-³H was studied by differential grain count in radioautographs of PPLO-free HeLa cells. It was found that the nucleolus is a site of rapid assembly or synthesis of a protein, the synthesis of which is inhibited equally by puromycin (200 µg/ml) and by actinomycin D under conditions inhibitory for ribosomal precursor RNA synthesis (P < 0.01). This protein is fixed by phosphate-buffered formalin or glutaraldehyde at pH 7.3, but the label is diminished by fixation in customarily employed acetic ethanol or in formalin at acid pH. Elevation of temperature of formalin or glutaraldehyde fixatives to 37°C consistently reduces the nucleolar protein label, but not the RNA label, by a proportion identical with that incurred by puromycin or actinomycin inhibition. This proportional reduction of nucleolar protein label occurs without evident loss of total grain count and is independent of length of fixation between 30 min and 4 hr, but it is not observed at 23°C. The data support the interpretation that the proportion of nucleolar protein not fixed at 37°C is associated with nucleolar ribosomal RNA but that it is dissociated at 37°C in formalin or glutaraldehyde fixatives, probably on the basis of ionic dissociation of a conjugated ribonucleoprotein.     

Cytochemical and autoradiographic ultrastructural study of the hairy cell

The ribosomal nature of the Hairy cell's Ribosome lamella Complex is given by cytochemical ultrastructural reactions. Using Autoradiography after tritiated uridine incubation no labelling was observed on the nucleolus and in the ribosome lamella Complex. Abnormalities in protein synthesis are thus demonstrated.