scholarly journals Quantitative alterations in the nucleolar and nucleoplasmic ribosomal ribonucleic acids in regenerating rat liver

1982 ◽  
Vol 204 (1) ◽  
pp. 179-183 ◽  
Author(s):  
Mariana D. Dabeva ◽  
Kalin P. Dudov
Keyword(s):  
Quantitative Analysis ◽  
Rat Liver ◽  
Rrna Processing ◽  
Regenerating Liver ◽  
Ribonucleic Acids ◽  
Regenerating Rat Liver ◽  
Rrna Species ◽  
The Absolute ◽  
Pool Sizes

A quantitative analysis of the nuclear pre-rRNA (precursor to rRNA) and rRNA in normal and 12h-regenerating rat liver was carried out, and the absolute amounts of the identified pre-rRNA and rRNA species in the nucleolus and nucleoplasm were determined. Characteristic changes in the pre-rRNA and rRNA pool sizes in regenerating liver are found which reveal alternations in both pre-rRNA processing and nucleocytoplasmic transition of ribosomes.

scholarly journals Post-transcriptional regulation of ribosome formation in the nucleus of regenerating rat liver

1983 ◽  
Vol 210 (1) ◽  
pp. 183-192 ◽  
Author(s):  
K P Dudov ◽  
M D Dabeva
Keyword(s):  
Rat Liver ◽  
Ribosome Biogenesis ◽  
Rrna Processing ◽  
Regenerating Liver ◽  
Regenerating Rat Liver ◽  
Rrna Species ◽  
Rrna Maturation ◽  
The Individual ◽  
Post Transcriptional Regulation

Kinetic experiments on RNA labelling in vivo with [14C]orotate were performed with normal and 12h-regenerating rat liver. The specific radioactivities of nucleolar, nucleoplasmic and cytoplasmic rRNA species were analysed by computer according to the models of rRNA processing and nucleo-cytoplasmic migration given previously [Dudov, Dabeva, Hadjiolov & Todorov, Biochem. J. (1978) 171, 375-383]. The rates of formation and the half-lives of the individual pre-rRNA and rRNA species were determined in both normal and regenerating liver. The results show clearly that the formation of ribosomes in regenerating rat liver is post-transcriptionally activated: (a) the half-lives of all the nucleolar pre-rRNA and rRNA species are decreased by 30% on average; (b) the pre-rRNA processing is directed through the shortest maturation pathway: 45 S leads to 32 S + 18 S leads to 28 S; (c) the nucleo-cytoplasmic transfer of ribosomes is accelerated. As a consequence, the time for formation and appearance of ribosomes in the cytoplasm is shortened 1.5-fold for the large and 2-fold for the small subparticle. A new scheme for endonuclease cleavage of 45 S pre-rRNA is proposed, which explains the alterations in pre-rRNA processing in regenerating liver. Its validity for pre-rRNA processing in other eukaryotes is discussed. It is concluded that: (i) the control sites in the intranucleolar formation of 28 S and 18 S rRNA are the immediate precursor of 28 S rRNA, 32 S pre-rRNA, and the primary pre-rRNA, 45 S pre-rRNA, respectively; (ii) the limiting step in the post-transcriptional stages of ribosome biogenesis is the pre-rRNA maturation.

scholarly journals Effects of γ-irradiation on biosynthesis of different types of ribonucleic acids in normal and regenerating rat liver

1975 ◽  
Vol 146 (1) ◽  
pp. 41-51 ◽  
Author(s):  
G G Markov ◽  
G N Dessev ◽  
G C Russev ◽  
R G Tsanev
Keyword(s):  
Partial Hepatectomy ◽  
Rat Liver ◽  
Cellular Response ◽  
Specific Radioactivity ◽  
Regenerating Liver ◽  
Γ Irradiation ◽  
Ribonucleic Acids ◽  
New Genes ◽  
Regenerating Rat Liver ◽  
Different Types

1. The effect of γ-irradiation (4000rd) on the synthesis of ribosomal (pre-rRNA) and heterogeneous nuclear RNA (pre-mRNA) in normal and in regenerating rat liver was studied by using 40 min labelling with [6(-14)C]orotic acid. 2. Partial hepatectomy caused a sharp transient increase in the specific radioactivity of the endogenous low-molecular-weight RNA precursors in the livers of both normal and irradiated rats. Irradiation of intact animals did not affect the pool. 3. Irradiation enhanced the synthesis of pre-rRNA for at least 12h. The synthesis of pre-mRNA was also enhanced, but only in the first 3h after irradiation. 4. Partial hepatectomy strongly stimulated the synthesis of both pre-rRNA and pre-mRNA. 5. The synthesis of pre-rRNA was enhanced also in regenerating liver of animals irradiated before or after the operation. The conclusion can be drawn that the early increase in the synthesis of ribosomal RNA is a non-specific cellular response to different injuring factors. 6. The only case where irradiation caused an early inhibition of RNA synthesis was that of pre-mRNA in regenerating liver. This supports the hypothesis that ionizing radiation does not suppress the transcription per se but affects the mechanisms of activation of new genes (cellular programming).

DEOXYCYTIDYLATE DEAMINASE LEVELS IN REGENERATING RAT LIVER

1961 ◽  
Vol 39 (6) ◽  
pp. 1043-1054 ◽  
Author(s):  
D. K. Myers ◽  
C. Anne Hemphill ◽  
Constance M. Townsend
Keyword(s):  
Dna Synthesis ◽  
Liver Regeneration ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
Deoxyribonucleic Acid ◽  
Regenerating Liver ◽  
Regenerating Rat Liver ◽  
High Level ◽  
Early Regeneration

Deoxycytidylate deaminase activity and net synthesis of deoxyribonucleic acid (DNA) in vivo were found to increase at approximately the same time during the early stages of liver regeneration. However, deaminase activity in the regenerating liver remained at a high level for 1 day after DNA synthesis had slowed down again during the later stages of regeneration. The increase in deaminase activity was restricted as a result of exposure to 600 r X radiation during early regeneration, but this effect only became evident 11–16 hours after the irradiation. Irradiation on the second day after partial hepatectomy, when deaminase levels in control regenerating livers were relatively constant, failed to affect the deaminase activity immediately but did produce a 40–50% decrease in activity 11–16 hours later. Other antimitotic agents, e.g., colchicine, had little effect on deaminase activity.

Cholesterol metabolism in regenerating liver of the rat

1985 ◽  
Vol 249 (6) ◽  
pp. G679-G684 ◽  
Author(s):  
F. J. Field ◽  
S. N. Mathur ◽  
D. R. LaBrecque
Keyword(s):  
Dna Synthesis ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
Cholesterol Synthesis ◽  
Cholesterol Metabolism ◽  
Reductase Activity ◽  
Plasma Cholesterol ◽  
Regenerating Liver ◽  
Acyltransferase Activity ◽  
Regenerating Rat Liver

The regenerating rat liver was used as a model to investigate the necessity for new cholesterol synthesis prior to the onset of cell division. Plasma cholesterol levels in partially hepatectomized rats were significantly decreased 24 and 48 h after surgery compared with levels in sham-operated animals. Hepatic cholesteryl ester content was also significantly increased in livers from partially hepatectomized animals, but the hepatic content of unesterified cholesterol was not affected. Hepatic triglyceride content was significantly increased within 6 h after surgery in the regenerating liver. The triglyceride levels reached a peak at 24 h, and by 72 h they had decreased back to levels that were no different from control. In the regenerating liver, microsomal 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase activity was increased 12 h after surgery. The activity of this enzyme remained significantly elevated throughout the 72-h period after surgery. In contrast, 12 h after partial hepatectomy the rate of hepatic cholesterol synthesis was significantly lower than that observed in livers from sham-operated rats. An increase in the rate of cholesterol synthesis was not observed until 48 h after partial hepatectomy, some 32 h after the start of DNA synthesis. Microsomal acyl-CoA:cholesterol acyltransferase activity was unchanged except for a 28% decrease at 72 h after partial hepatectomy. The data suggest that new cholesterol synthesis is not a requirement prior to the initiation of DNA synthesis in the regenerating rat liver.(ABSTRACT TRUNCATED AT 250 WORDS)

RIBONUCLEASE ACTIVITY IN REGENERATING RAT LIVER

1967 ◽  
Vol 45 (7) ◽  
pp. 1021-1026 ◽  
Author(s):  
D. J. S. Arora ◽  
G. de Lamirande
Keyword(s):  
Enzymatic Activity ◽  
Liver Regeneration ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
Ribonucleic Acid ◽  
Ribonuclease Activity ◽  
Regenerating Liver ◽  
Early Stages ◽  
Regenerating Rat Liver ◽  
Ribonucleoprotein Particles

Ribonucleoprotein particles were isolated from sham-hepatectomized and partially hepatectomized animals. The levels of ribonucleic acid and of proteins, as well as the ribosomal ribonuclease activity, have been studied in regenerating liver at periods of 4, 8, 16, 36, and 72 hours after partial hepatectomy. The results showed that the amount of ribosomes in regenerating rat liver was not affected as compared with the level observed in sham-operated rats. However, a decrease of ribonuclease activity was noticed in the early stages of liver regeneration. The ribonuclease activity was practically negligible at 16 and 36 hours. Less than 50% of the enzymatic activity was regained at the 72-hour period after partial hepatectomy.Results show that the ribosomes from regenerating liver are more stable and the stabilizing factor seems to be the absence of ribonuclease.

scholarly journals Growth of liver accompanied by an increased binding of aminoacyl-transfer ribonucleic acids

1977 ◽  
Vol 166 (3) ◽  
pp. 463-471 ◽  
Author(s):  
D McEwen Nicholls ◽  
J Carey ◽  
W Sendecki
Keyword(s):  
Rat Liver ◽  
Inhibitory Activity ◽  
Elongation Factor ◽  
Supernatant Fraction ◽  
Regenerating Liver ◽  
Ribosomal Subunits ◽  
Ribonucleic Acids ◽  
Aminoacyl Transfer ◽  
Elongation Factor 1 ◽  
Trna Binding

Homogenates of rat liver obtained 3 or 14 days after partial hepatectomy were used to prepare the postmicrosomal pH5-supernatant fraction and to prepare salt-wash fractions of the 40S ribosomal subunits and the 80S ribosomes. The factor-dependent binding of methionyl-tRNAfMet to ribosomes and the elongation-factor-1-dependent binding of phenylalanyl-tRNA to ribosomes were both increased after 3 days of growth, but not after 14 days of growth. An activity inhibitory to phenylalanyl-tRNA binding that was located in ribosomal wash fractions was decreased after 14 days of growth. Since the decreased inhibitory activity was obtained from the ribosomes and was tested against ribosomes and excess of pH5-supernatant fraction from control rat liver, its action was separate from the phenylalanyl-tRNA binding activities of the pH5-supernatant fractions from sham-operated and regenerating liver.

scholarly journals Differential stability of 28s and 18s rat liver ribosomal ribonucleic acids

1969 ◽  
Vol 115 (1) ◽  
pp. 91-94 ◽  
Author(s):  
P. V. Venkov ◽  
A. A. Hadjiolov
Keyword(s):  
Rat Liver ◽  
Gel Electrophoresis ◽  
18S Rrna ◽  
Heterogeneous Material ◽  
28S Rrna ◽  
Agar Gel ◽  
Ribonucleic Acids ◽  
Different Temperatures ◽  
Rrna Species ◽  
Agar Gel Electrophoresis

Rat liver ribosomal RNA (rRNA) free from nuclease contaminants was isolated by a modification of the phenol technique. The 28s and 18s rRNA species were separated by preparative agar-gel electrophoresis. The two rRNA species were heated at different temperatures under various conditions and the amount of undegraded rRNA was determined by analytical agar-gel electrophoresis. The 18s rRNA remained unaltered after heating for up to 10min. at 90° in water, acetate buffer, pH5·0, or phosphate buffer, pH7·0. Under similar or milder conditions 28s rRNA was partially degraded, giving rise to a well-delimited 6s peak and a heterogeneous material located in the zone between 28s and 6s. The dependence of degradation of 28s rRNA on the temperature and the ionic strength of the medium was studied. The greatest extent of degradation of 28s rRNA was observed on heating at 90° in water. It is suggested that the instability of rat liver 28s rRNA is due to two factors: the presence of hidden breaks in the polymer chain and a higher susceptibility of some phosphodiester bonds to thermal hydrolysis.

EFFECT OF CORTICOTROPHIN AND CORTISONE ON THE INCORPORATION OF 3H-THYMIDINE INTO THE DEOXYRIBONUCLEIC ACIDS (DNA) OF THE REGENERATING LIVER IN THE WHITE RAT

1968 ◽  
Vol 59 (1) ◽  
pp. 10-22 ◽  
Author(s):  
Jan W. Guzek
Keyword(s):  
Dna Synthesis ◽  
Mitotic Activity ◽  
Rat Liver ◽  
Regenerating Liver ◽  
Regenerating Rat Liver

ABSTRACT Both cortisone and ACTH inhibit the incorporation of 3H-thymidine into the DNA of parenchymatous cells in the regenerating rat liver. In addition, the mitotic activity of hepatocytes is markedly impaired. It is assumed that the suppression of mitoses in the regenerating rat liver, caused by cortisone or ACTH, is due to a direct or indirect interference with DNA synthesis.

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