Ribosomal RNA synthesis in haploid and diploid loach embryos]

rRNA synthesis was compared in the loach haploid (In) and diploid (2n) embryos. The relative intensity of synthesis was evaluated by 14C-uridine incorporation in 27S and 18S rRNA isolated from ribosomes taking into account label incorporation into total acid-soluble fraction and phosphrylated uridine derivatives. Label incorporation into rRNA, in reference with DNA content in 1n and 2n embryos, suggests that the level of rRNA synthesis per DNA unit in haploids is twice that in diploids whereas, in reference per cell, the same amount of ribosomes is synthesized both in haploids and diploids. The data obtained show that the amount of rRNAs synthesized in the loach embryogenesis does not depend on ploidy.     

Inhibition of RNA synthesis in animal cells by sodium selenite

The effect of selenium-containing compounds on RNA synthesis in rat liver cells was studied in vivo. All the selenium derivatives under study inhibited the rRNA synthesis in liver cells. The most potent inhibiting effect was exerted by sodium selenite. It was shown that in a cell-free system of RNA biosynthesis sodium selenite selectively inhibited the activity of RNA-polymerase I in isolated nuclei and purified enzyme preparations of normal and tumour cells. A feasible mechanism of inhibition of the RNA-polymerase I activity by selenium and a hypothesis on the anticarcinogenic effect of selenium are postulated.     

Effect of norfloxacin on ultrastructure characteristics of the loach embryos

The ultrastructure of embryo cells of the loach (Misgurnus fossilis L.) at the stage of the first and the tenth blastomer divisions in the control and under the conditions of fluoroquinolone norfloxacin (5 and 25 mkg/ml) influences has been investigated. The effect of this antibiotic has resulted in significant ultrastructural changes of embryo cells, such as hypertrophy of channels of the smooth and rough endoplasmic reticulum, disorganization of mitochondrias and cytoplasm membrane destructions of embryo. It has been established that fluoroquinolone inhibited biosynthetic processes, directly influencing on the blastomer biosynthetic structures. Such results testify a high norfloxacin embryotoxicity.     

Effect of avermectin on the ultrastructural characteristics of loach embryos

The ultrastructure of loach (Misgurnus fossilis L.) embryo cells at the stages of the first and tenth blastomere divisions in the presence of avermectin B (a compound that belongs to the class of macrocyclic lactones, avermectins) in an incubation medium at concentrations of 0.01, 0.1, and 1.0 μg/ml was studied. It was found that the effect of this compound led to ultrastructural changes in cell organelles, such as hypertrophy of the granular and agranular endoplasmic reticulum and disorganization of the mitochondria and the embryo plasma membrane. Avermectin activity causes dose-dependent destructive changes in organelles; such changes are the consequences of the destruction of metabolic and regulatory processes, caused by the inhibitory influence of avermectin on the processes of active transport of Na⁺, K⁺ and Ca²⁺ ions. The data obtained in this study show that avermectin is characterized by high embryotoxicity.     

Activation of RNA synthesis in loach embryos after injection of a nuclear extract obtained by using 0.35 M NaCl

An extract mainly containing chromatin nonhistone proteins was obtained by means of 0.35 M NaCl from nuclei isolated from loach (Misgurnus fossilis L.) embryos at the 18 hour developmental stage (late gastrula). Injection of a concentrated nuclear extract into the loach eggs was followed by intensified (1.5--2.0 fold) incorporation of radioactive precursors [3H]uridine or 14CO2 into RNA. The stage at which natural activation of the RNA synthesis occurs (6 hours, mid blastula) remains unchanged, but the rate of incorporation after the onset of synthesis activation (8 hours, late blastula) becomes greater.     

Influence of sodium selenite and selenomethionine on DNA/RNA synthesis and BaP binding to spleen lymphocytes in culture

In the present study, an attempt was made to provide some information regarding the effects of organic and inorganic selenium compounds on DNA/RNA synthesis and benzo(a)pyrene uptake in cultured lymphocytes from mice spleen. It was clear from the results that there was a significant inhibition of DNA/RNA synthesis with increasing concentration of either form of selenium from 0.1ΜM to 1 mM in culture medium. However, when used at the same level as selenite with respect to selenium content, selenomethionine exerted more DNA/RNA synthesis inhibitory effect than selenite. Benzo(a)pyrene uptake by proliferating lymphocytes was also significantly reduced with increasing selenium concentration (0.1 ΜM to 1 mM). However, both forms of selenium at the same selenium concentration showed almost the same inhibitory effect on the cellular uptake of benzo(a)pyrene, which indicated that some factor(s) other than the DNA synthesis are also involved in the interaction between benzo(a)pyrene and cells. Involvement of the changes in the carcinogen metabolism and glutathione level has been discussed. Present studies show that organic selenium as a source of selenium is a more potent chemopreventive compared to the inorganic one. This information may have a useful therapeutic potential.     

Effect of anionic surfactants on some dehydrogenases and phosphofructokinase activities in loach embryos

Glucose-6-phosphatedehydrogenase (EC 1.1.1.49), lactatedehydrogenase (EC 1.1.1.27), malate dehydrogenase (EC 1.1.1.38) and phosphofructokinase (EC 2.7.1.11) activities in loach (Misgurnus fossilis L.) embryos were determined after incubation of the latter in the media containing surfactants--alkyl benzol sulphonates NP-1, NP-3, RAS and secondary alkyl sulphate "Progress". The determined activities changed under the influence of the used surfactants. Minimal changes of the activities were observed in the media with sulphonol np-1, and maximal ones--with the "Progress" preparation. The dependence is revealed of the enzyme activities changes upon the surfactant concentration and the stage of the embryo development.     

Kinetics of the synthesis of nucleic acids in haploid and diploid loach embryos]

Al kinetic analysis of incorporation of the mixture of 3H-nucleosides in the nucleic acid fractions was carried out to examine the mechanisms of compensation of the genetic material deficiency. Both the haploid and diploid embryos of the loach (Misgurnus fossilis L.) were analyzed. When comparing the DNA and RNA syntheses, the level of phosphorylation (nucleotide pool) in the both genetic variants was under control. The rate of incorporation of the labelled nucleosides in DNA was shown to be higher in haploids at the early developmental stages than in diploids but later it became the same. The increased level of DNA replication in the early haploid embryos was due to the compensatory increase of the cell number in them as compared with the diploid ones. The rate of total RNA synthesis corrected by the differences in the rate of nucleoside phosphorylation varied directly with the degree of ploidy at the blastula stage; at the gastrula stage the value of RNA synthesis per haploid genome was compensated, and at the stage of organogenesis the production of total RNA, as calculated per cell, became in haploids even higher than in diploids. The data obtained suggest the essential changes in the patterns of RNA synthesis control during development.     

RNA and protein synthesis in preimplantation rabbit embryos

A phenol-sodium dodecyl sulfate procedure has been used to extract DNA, RNA, and protein from 3-, 4.5-, and 6.5-day-old preimplantation rabbit embryos that were incubated for different lengths of time in the presence of labeled precursors. The results suggest that the newly-synthesized RNA and protein are more stable in the growing blastocyst than in the trophoblast at the time of implantation.This conclusion was derived from the results of embryo incorporation kinetics. The results also suggest that the increase in protein and RNA content in preimplantation rabbit blastocysts was preceded by an increase in protein synthesis accompanied by low catabolism.     

Effect of chemical animalization and vegetalization on the synthesis of ribosomal RNA in sea urchin embryos

Summary Treatment of embryos of Paracentrotus lividus with a concentration of ZnSO₄ which causes animalization, strongly inhibits the initiation of ribosomal RNA synthesis.The vegetalizing agent LiCl does not seem clearly to affect the synthesis of this RNA.

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Zusammenfassung In mit ZnSO₄ animalisierten Embryonen von Paracentrotus lividus ist der Beginn der ribosomalen RNS-Synthese stark gehemmt.Das vegetalisierende LiCl scheint nicht die Synthese dieser RNS zu beeinflussen.

     

Effects of alpha-amanitin on RNA synthesis by mouse embryos in culture

Investigations were conducted to test the effects of alpha-amanitin on RNA synthesis in preimplantation mouse embryos. Exposure of embryos in culture to 1-100 microgram/ml alpha-amanitin produced a dose- and time-dependence suppression of total RNA synthesis as measured by incorporation of [3H]uridine. Synthesis of polyadenylated RNA in blastocyst-stage embryos was abolished by alpha-amanitin-treatment at concentrations and exposure times that suppressed total RNA synthesis by less than 15%. DNA-dependent RNA polymerase activity was measured in lysates of embryos at several stages of preimplantation development. alpha-Amanitin suppressed total polymerase activity assayed under ionic conditions favorable to the detection of RNA polymerase II. Electrophoretic analyses revealed that preincubation of blastocysts in 100 microgram/ml alpha-amanitin reduced labelling of cytoplasmic 28S and 18S RNA by inhibition of both synthesis and maturation of nucleolar 45SrRNA-precursor. This action of alpha-amanitin on nucleolar RNA synthesis cannot be correlated with the minimal suppression of nucleolar RNA polymerase activity and suggests that the synthesis and processing of rRNA may be under control of nucleoplasmic gene products.