Effect of -amantine on puffing and intranuclear RNA synthesis in Chironomus salivary glands

The ribosome biogenesis pathway as an early target of benzyl butyl phthalate (BBP) toxicity in Chironomus riparius larvae

Butyl benzyl phthalate (BBP) is a ubiquitous contaminant whose presence in the environment is expected for decades, since it has been extensively used worldwide as a plasticizer in the polyvinyl chloride (PVC) industry and the manufacturing of many other products. In the present study, the interaction of BBP with the ribosome biogenesis pathway and the general transcriptional profile of Chironomus riparius aquatic larvae were investigated by means of changes in the rDNA activity (through the study of the internal transcribed spacer 2, ITS2) and variations in the expression profile of ribosomal protein genes (rpL4, rpL11, and rpL13) after acute 24-h and 48-h exposures to a wide range of BBP doses. Furthermore, cytogenetic assays were conducted to evaluate the transcriptional activity of polytene chromosomes from salivary gland cells, with special attention to the nucleolus and the Balbiani rings (BRs) of chromosome IV. BBP caused a dose and time-dependent toxicity in most of the selected biomarkers, with a general depletion in the gene expression levels and the activity of BR2 after 48-h treatments. At the same time, decondensation and activation of some centromeres took place, while the activity of nucleolus remained unaltered. Withdrawal of the xenobiotic allowed the larvae to reach control levels in the case of rpL4 and rpL13 genes, which were previously slightly downregulated in 24-h tests. These data provide the first evidence on the interaction of BBP with the ribosome synthesis pathways, which results in a significant impairment of the functional activity of ribosomal protein genes. Thus, the depletion of ribosomes would be a long-term effect of BBP-induced cellular damage. These findings may have important implications for understanding the adverse biological effects of BBP in C. riparius, since they provide new sensitive biomarkers of BBP exposure and highlight the suitability of this organism for ecotoxicological risk assessment, especially in aquatic ecosystems.

Cytogenetic index and functional genome alterations in Chironomus piger Strenzke (Diptera, Chironomidae) in the assessment of sediment pollution: a case study of Bulgarian and UK rivers

The genotoxicity of trace metals in the sediments from a number of polluted sites on UK and Bulgarian rivers to Chironomus piger was assessed by an examination of genome instability as demonstrated by structural and functional changes to the salivary glands chromosomes. Based on the metal assays, the sediments were characterized to range from 'extremely' to 'strongly contaminated'. The cytogenetic index calculated on the basis of somatic structural chromosome alterations in the polytene chromosomes indicates a high level of pollution (0.07-0.06 in Bulgarian and 0.10-0.13 in UK stations). Exposure of C. piger to contaminated sediments resulted in a high level of chromosome damage as indicated by a somatic index of between 1.96 and 4.0. The transcription mechanism of the Balbiani rings and nucleolar organizer was damaged as their activity was either partially or completely suppressed. We have demonstrated that the C. piger genome is a sensitive sublethal indicator of sediment contamination, and is a highly suitable candidate for ecotoxicological monitoring of running waters.

Does biodiversity of macroinvertebrates and genome response of Chironomidae larvae (Diptera) reflect heavy metal pollution in a small pond?

The investigation was carried out on a small pond situated on a recent mine spoil at Bolesław in the Olkusz region with Zn-Pb ore deposits. Water of the pond had pH 7.2-8.5 and low concentrations of heavy metals. Concentrations of Pb (487 μg g( - 1)) and Zn (1,991 μg g( - 1)) in the sediment were very high and potentially could lead to toxicological effects. In the pond, 48 taxa of macroinvertebrates belonging to Oligochaeta and water stages of Ephemeroptera, Odonata, Megaloptera, Trichoptera, Heteroptera, Coleoptera and Diptera (mainly Chironomidae family) were found. The influence of heavy metals on macroinvertebrates diversity was not found. Effect of heavy metal pollution was observed on the appearance of chromosome aberrations in the polytene chromosomes of Chironomidae larvae. It was manifested by two ways: (1) in Kiefferulus tendipediformis and Chironomus sp. chromosome rearrangements in fixed state (tandem fusion and homozygous inversions), indicated intensive process of speciation; (2) in Chironomus sp., K. tendipediformis, Glyptotendipes gripekoveni (Chironomidae) somatic chromosome rearrangements (inversions, deficiencies, specific puffs, polyploidy) affected few cells of every individual. The somatic functional and structural alterations in Chironomidae species are particular suitable as biomarkers-they can be easily identified and used for detecting toxic agents in the environment.

Ribosomal genes as early targets of cadmium-induced toxicity in Chironomus riparius larvae

Cadmium is a widespread environmental pollutant that causes severe impacts in organisms. Although the effects of cadmium on aquatic insects have been studied in terms of their toxicity and changes in developmental parameters, little is known about its molecular and genetic effects. We have investigated the alterations in the pattern of gene expression provoked by acute exposure to cadmium in Chironomus riparius Mg. (Diptera, Chironomidae), a sentinel organism widely used in aquatic toxicity testing. The early cytotoxic effects were evaluated using immunocytochemistry and specific fluorescent probes in fourth instar larvae after 12 h of 10 mM cadmium treatments; under these conditions no significant effect on larvae mortality was detected until after 36 h of exposure. The changes in the pattern of gene expression were analysed by means of DNA/RNA hybrid antibodies in the polytene chromosomes from salivary gland cells. A decrease in the activity of the nucleolus is especially remarkable, accompanied by a significant reduction in size and the modification in nucleolar architecture, as shown by FISH. The inhibition of rDNA transcription was further evaluated by Northern blot analysis, which showed a marked decrease in the level of preribosomal rRNA (54% 45S 12 h). However, the BR genes, whose products are the giant polypeptides that constitute the silk-like secretion for constructing housing tubes, remain active. Simultaneously, decondensation and activation take place at some chromosomal regions, especially at the centromeres. The changes observed in the pattern of gene expression do not resemble those found after heat shock or other cell stressors. These data provide the first evidence that cadmium interacts with ribosomal genes and results in a drastic impairment of the functional activity of the nucleolus, an essential organelle for cellular survival. Therefore, the depletion of ribosomes would be a long-term effect of Cd-induced cellular damage. These findings may have important implications for understanding the adverse biological effects of cadmium and its toxic mechanism, as yet not clearly defined, and provide a sensitive biomarker of cadmium exposure.

Genotoxic effect of copper on salivary gland polytene chromosomes of Chironomus riparius Meigen 1804 (Diptera, Chironomidae)

The genotoxic action of copper (Cu) on the polytene chromosomes of Chironomus riparius was investigated by analysing structural and functional chromosome aberrations of fourth instars larvae hatched from eggs subject to acute (48 h) exposure with three environmentally relevant concentrations of aqueous Cu (0.005, 0.01, 0.05 mg/l). A dose dependent relationship was observed between Cu concentration and frequency of chromosomal aberrations. A significantly higher frequency of functional alterations, specifically decondensed centromeres and telomeres, and reduction in activity of Balbiani rings, was observed in treated material compared to control. A comparison of breakpoints resulting from treatment with chromium and lead from earlier studies with those Cu-induced identified a series of chromosomal weak points particularly vulnerable to trace metals. We also show that the appearance of structural and functional chromosome aberrations are more sensitive indicators of acute Cu toxicity in chironomid larvae than changes in external morphology.

Functional and structural rearrangements of salivary gland polytene chromosomes of Chironomus riparius Mg. (Diptera,Chironomidae) in response to freshly neutralized aluminium

Although recent work has shown that environmentally relevant concentrations of freshly neutralized aluminium (AI) are bioavailable and toxic to freshwater invertebrates, the genotoxicity of Al has not been examined. Here we show that freshly neutralized Al affects structure and function of the salivary gland polytene chromosomes of the ubiquitous chironomid larva Chironomus riparius over three generations. Exposure to 500 microg l-1 added Al for 24-25 days resulted in a significantly higher frequency of numerous somatic aberrations, while no structural aberrations were found in F1 controls and few in the second and third generation. Aberrations also included deletions of sections of chromosome G of C. riparius larvae as well as deletions of one or more Balbiani rings. Changes in functional activity included decreased activity of the Balbiani rings (BR), and an increase in the number of decondensed centromeres. The activity of the nucleolar organizer (NOR) significantly decreased in F1 chironomids exposed to Al, while in the F2 and F3 generations the NOR showed normal (high) activity. First generation chironomids were generally more susceptible to Al although no clear evidence of tolerance was apparent over three generations. The possible use of alterations in chironomid polytene chromosomes as biomarkers of trace metal pollution is discussed.

Ecdysone-controlled mRNA stability in Drosophila salivary glands: deadenylation-independent degradation of larval glue protein gene message during the larval/prepupal transition

20-Hydroxyecdysone induces poly(A) shortening and the subsequent degradation of transcripts encoding the larval glue protein LGP-1 in Drosophila virilis late third larval instar salivary glands. Degradation concurs with the transient increase of ribonucleolytic activities in the gland cells. In vitro nuclease assays using crude cytoplasmic extracts of ecdysone-treated salivary glands demonstrate degradation to be deadenylation-independent and that the induced ribonucleolytic activities initiate the degradation of the Lgp-1 transcripts in putative single-stranded loop regions. The independence of degradation from deadenylation is also found in vivo in transformed D. melanogaster carrying a modified Lgp-1 gene.

Induction of the heat-shock response by carbon dioxide in Chironomus thummi

The effects of a set of stress treatments on gene expression of Chironomus thummi salivary gland cells have been analyzed. Among the treatments assayed, only during recovery from carbon dioxide have we observed a response similar to that previously described after heat-shock treatment: induction of the heat-shock puffs and synthesis of the heat-shock polypeptides. In these conditions, puffing and transcription of telomeric regions were observed, which led to the appearance of the temperature-inducible telomeric Balbiani ring T-BR-III. Other treatments failed to induce the heat-shock response, despite promoting real stress conditions to C. thummi larvae or salivary gland cells.

Mutations in rDNA : 3. Modulatory action of α-amanitin on aberration induction in nucleolus organizer regions

The action of α-amanitin, an inhibitor of RNA synthesis, on the induction by hydroxyurea (HU) of chromosomal aberrations in nucleolus organizer regions of barley was studied. The data obtained show that α-amanitin can effectively modify aberration induction in rDNA. Administered before mutagen treatment or in combination with the mutagen, the toxin significantly decreased the HU-induced aberration frequencies in NORs. The data obtained provide further evidence that α-amanitin is an effective modulator of aberration induction in NORs either by interfering with RNA synthesis or by modifying chromatin structure.

RNA polymerase B in polytene chromosomes: immunofluorescent and autoradiographic analysis during stimulated and repressed RNA synthesis

The distribution of RNA polymerase B (or II) in native and fixed polytene chromosomes isolated from salivary glands of Chironomus tentans and C. pallidivittatus was investigated by both indirect immunofluorescence and autoradiography. The chromosomes, especially the Balbiani rings (BR2, BR1 and BR3), were examined during periods of stimulated and repressed RNA synthesis. In repressed BR2a and, after the salivary gland chromosomes had been stretched, in various chromosomal segments, it was possible to establish unequivocally that RNA polymerase B is not confined to puffs, but also occurs in interbands. The enzyme was absent from the bands, or at least there was not enough of it to be detected with indirect immunofluorescence. It was shown that the distribution of the indirect immunofluorescence in the chromosomes concurs with that of the 3H-uridine or 3H-UTP labeling. However, RNA polymerase B molecules remain associated with the chromosomal template even after an in vivo alpha-amanitin or actinomycin D treatment to inhibit RNA synthesis. Following heat shocks (37 degrees C to 39 degrees C), transcriptively active RNA polymerase B is still found in interbands, in the BRs and in other puffs that have collapsed as a result of the heat treatment; the greatest enzyme concentrations, however, are in the stimulated heat-shock puffs.

Effects of DMSO on the structure and function of polytene chromosomes of Chironomus

Dimethylsulfoxide (DMSO) controlled puff induction and repression (or non-induction) in larval polytene chromosomes of Chironomus tentans were studied for the case of the Balbiani rings (BR). A characteristic reaction pattern, involving BR 1, BR 2, and BR 3, all in salivary gland chromosome IV was found. In vivo exposure of 4th instar larvae (not prepupae) to 10%n DMSO at 18 degrees C first evokes an over-stimulation of BR 3 while DMSO-stimulation of puffing at BR 1 and BR 2 always follows that of BR 3. After removal of the drug, a rapid uniform collapse of all puffs occurs, thus more or less restoring the banding pattern of all previously decondensed chromosome segments. Recovery proceeds as BR's and other puffs reappear. By observing the restoration, one can locate the site from which a BR (puff) originates. BR 2, which is normally the most active non-ribosomal gene locus in untreated larvae, here serves as an example. As the sizes of BR 3, BR 1 and BR 2 change, so do the quantities of the transcriptional products in these gene loci (and vice versa), as estimated electron-microscopically in ultrathin sections and autoradiographically in squash preparations. In autoradiograms, the DMSO-stimulated BRs exhibit the most dense concentration of silver grains and therefore the highest rate of transcriptional activity. In DMSO-repressed BRs (and other puffs) the transcription of the locus specific genes is not completely shut off. In chromosomes from nuclei with high labelling intensities the repressed BRs (and other puffs) always exhibit a low level of 3H-uridine incorporation in vivo. The absence of cytologically visible BR (puff) formation therefore does not necessarily indicate complete transcriptional inactivity. Typically, before the stage of puff formation the 3H-uridine labelling first appears in the interband-like regions.

Study of salivary gland specific transcripts in Chironomus tentans by cDNA analysis

Preparative amounts of polyA-containing RNA were purified from isolated salivary glands from Chironomus tentans and used as a template for the synthesis of cDNA by AMV reverse transcriptase. The yield of cDNA corresponded to 8-14% of the input polyA RNA. Using the Alwine hybridization method (Alwine et al., 1977) it was shown that only a minor part of the cDNA hybridized to the 75S RNA band and that the major hybridization occurred to a hitherto unknown gland-specific polyA RNA transcript of 1.3 kb length. In addition, the cDNA hybridized to a gland-specific polyA-RNA transcript of 2 kb length. - The majority of the cDNA had a size of 0.4 or 0.7 kb in equal amounts. A Southern hybridization of the cDNA to an EcoRI digest of genomic DNA showed in addition to a very weak hybridization to the 40 kb band of the Balbiani ring genes, hybridization to several restriction fragments with sizes from 1.3 to 16 kb.

Temperature-induced Balbiani rings in Chironomus thummi

The formation of a new telomeric Balbiani ring in the right arm of chromosome III (T-BR III) has been induced in Chironomus thummi larvae by applying a wide range of temperature treatments (33 degrees - 39 degrees C). In this paper we present some kinetic and functional characteristics of this structure. T-BR III incorporates tritiated uridine, and during its formation accumulation of acidic proteins takes place. However, induction and maintenance of this puff structure appear to be insensitive to Actinomycin treatment. An additional T-BR can be induced in chromosome I by employing the most drastic temperature treatments (37 degrees - 39 degrees C). We also report the existence of a group of puffs active after heat treatments in Chironomus polytene chromosomes which could be homologous with the T-puffs of Drosophila.

Dependence of Balbiani ring puffing on protein synthesis

The possible dependence of puffing of the Balbiani rings (BRs) on the protein synthesis has been investigated by studying the response of these structures to protein synthesis inhibition induced by cycloheximide and anisomycin. When larvae of Chironomus thummi belonging to middle IV instar (BR1 repressed, BR2 expanded) are subjected to short treatment (3--6 h) with these drugs, BR1 and BR2 puffing states remain essentially unaffected. But when the same treatments are applied to galactose-pretreated larvae (BR1 expanded, BR2 repressed), selective reactivation of the collapsed BR2 occurs. These observations suggest that maintenance of a given puffing state can be dependent, to a variable extent, on the supply of newly synthesized proteins. In particular, selective re-expansion of galactose-repressed BR2 induced by the drugs seem to indicate the existence of repressor-like factor whose activity would be triggered by the galactose treatment.

Features of in vitro puffing and RNA synthesis in polytene chromosomes of Chironomus

In order to elucidate the causal relation between RNA synthesis and puffing in polytene chromosomes, salivary gland nuclei and chromosomes from Chironomus tentans and C. pallidivittatus (Diptera, Chironomidae) were isolated in the native state under controlled and optimized conditions. The behavior of the polytene chromatin in vitro as compared to that in vivo was studied morphologically and autoradiographically. It was shown that the absence of cytologically visible puffing does not necessarily indicate transcriptional quiescence. Under suitable conditions all potential puff sites incorporate the radioactive precursor simultaneously. This can be seen in vivo and even more clearly in chromosomes decondensed by 340-400 mM NaCl in vitro. Potential puff sites therefore appear to be permanently equipped with RNA-polymerases, and there is always a basic low level of transcriptive activity. Experimental shrinking of Balbiani rings and other puffs by dimethylsulfoxide (DMSO) or heat shock in vivo, leaves the genes in the collapsed puffs still transcriptionally active, although to a reduced extent. Light optically visible puffing is therefore not a necessary prerequisite for RNA synthesis, while, conversely, RNA synthesis is required for puff formation.

Amatoxins, phallotoxins, phallolysin, and antamanide: the biologically active components of poisonous Amanita mushrooms

This review gives a comprehensive account of the molecular toxicology of the bicyclic peptides obtained from the poisonous mushrooms of the genus Amanita. The discussion of the biochemical events will be preceded by a consideration of the chemistry of the toxic peptides. The structural features essential for biological activities of both the amatoxins and the phallotoxins will be discussed, also including the most important analytical data. Similar consideration will be given to antamanide, a cyclic peptide, which counteracts phalloidin. In addition, the phallolysins, three cytolytic proteins from Amanita phalloides will be discussed. The report on the biological activity of the amatoxins will deal with the sensitivity of the different RNA-polymerases towards the toxins and with their action on various cell types. Consideration will also be given to systems in which alpha-amanitin was used and can be used as a molecular tool; in the past, many investigators used the inhibitor in molecular biology, genetics, and even in physiological research. As for the phallotoxins, discussion of the affinity of these toxins for actin is provied. Further discussion attempts to understand the course of intoxication by filling in the gap between the first molecular event, formation of microfilaments, and the various lesions in hepatocytes during the intoxication.

Effect of galactose treatment in the puffing pattern of Chironomus thummi Balbiani rings

Galactose feeding of Chironomus thummi larvae induces the regression of Balbiani ring c (BRc) and the full expansion of BRb, both localized in the IV salivary gland chromosome. This effect coincides with that described on BR2 and BR1 of Ch. pallidivittatus and Ch. tentans. The puffing changes of BRb and BRc throughout develoment have been studied and also show identical variations as in BR1 and BR2 of Ch. pallidivittatus and Ch. tentans. The similar behaviour of BRb and BR1, and of BRc and BR2 respectively after galactose treatment and throughout development strongly suggests that these BRs play the same physiological role in the three Chironomus species, with BRb = BR1 and BRc= BR2.

Distribution of RNA polymerase on Drosophila polytene chromosomes as studied by indirect immunofluorescence

Using indirect immunofluorescence visualization techniques we investigated the in situ distribution of RNA polymerase B on Drosophila melanogaster polytene chromosomes. The enzyme was found at many sites distributed throughout the genome in a pattern clearly distinct from that observed for histone H1, but it was especially concentrated in puffs induced by heat shock.

In vitro transcription by isolated nuclei of Rhynchosciara americana salivary glands. Characteristics of incorporation and inhibition by alpha-amanitin

A method for the isolation of polytene nuclei from salivary glands cells of the Diptera Rhynchosciara americana is described. The stage-specific morphological pattern of the chromosome is maintained during the isolation. The isolated nuclei show two distinct RNA polymerase activities, namely I and II, characterized on the basis of ionic requirements and alpha-amanitin sensitivity. Studies of the product under the incubation conditions show that the system allows the synthesis of high-molecular weight RNA, beside a low molecular weight peak which may comprise pre-4S and 5S RNAs. Autoradiographic studies carried out in the presence or absence of the toxin alpha-amanitin showed that micronucleoli contain products of RNA polymerase type I activity (ribosomal RNA) and that the DNA puffs are engaged in alpha-amanitin sensitive RNA synthesis and thus are sites of polymerase type II activity.

Effects of alpha-amanitine on chromatin in regenerating rat hepatocytes: a biochemical and morphologic study

Almost all the chromatin in nuclei of regenerating rat liver hepatocytes 15 h and particularly 24 h after partial hepatectomy appeared as decondensed chromatin. Treatment with alpha-amanitine induced a clear condensation of decondensed chromatin as early as 30 min after toxin injection. The degree of condensation increased further until, 2 h after poisoning, almost all the chromatin was found to be in condensed form. Because the synthesis of DNA, after toxin injection, was not modified during the first 2h and 30 min, our results indicate that the chromatin condensation did not affect the synthesis of DNA. In the present paper the relationships between the inhibition of RNA synthesis and the chromatin ultrastructural changes are also discussed.

Cycloheximide-induced ultrastructural changes in hepatocyte nuclei in partially hepatectomized rats

Nearly all the chromatin in regenerating rat hepatocytes appears to decondensed form 24 h after partial hepatectomy. When cycloheximide (CXM) is administered to partially hepatectomized rats, a marked condensation of chromatin occurs; 4 h after administration the quantity of condensed chromatin present is much higher than that found in the hepatocytes of sham-operated, untreated rats. No segregation or fragmentation of the nucleolus were, however, observed; this shows that the condensation of chromatin is not by itself sufficient to induce the segregation and fragmentation of the nucleolus. The mechanism governing CMX-induced chromatin condensation in regenerating hepatocytes is discussed.

The action of alpha-amanitin on RNA synthesis in Chinese hamster ovary cells. Ultrastructural and biochemical studies

alpha-Amanitin acts in vitro as a selective inhibitor of the nucleoplasmic form B RNA polymerases. Treatment of Chinese hamster ovary (CHO) cells with this drug leads principally to a severe fragmentation of the nucleoli. While the ultrastructural lesions induced by alpha-amanitin in CHO cells and in rat or mouse liver are quite similar, the results diverge concerning the effect on RNA synthesis. It has been shown that in rat or mouse liver alpha-amanitin blocks both extranucleolar and nucleolar RNA synthesis. Our autoradiographic and biochemical evidence indicates that in CHO cells high molecular weight extranucleolar RNA synthesis (HnRNA) is blocked by the alpha-amanitin treatment, whereas nucleolar RNA (preribosomal RNA) synthesis remains unaffected even several hours after the inhibition of extranucleolar RNA synthesis. Furthermore, the processing of this RNA as well as its transport to the cytoplasm seem only slightly affected by the treatment. Finally, under these conditions, the synthesis of the low molecular RNA species (4-5S) still occurs, though less actively. The results are interpreted as evidence for a selective impairment of HnRNA synthesis by alpha-amanitin in CHO cells.

[Localisation of the α-amanitin-sensitive RNA-polymerase in nuclei of Acetabularia]

An isolation medium for nuclei of Acetabularia mediterranea is described. The medium offers the possibility to keep nuclei alive (verified by reimplantation) for at least 10 min and to obtain nuclei with radioactively labelled RNA.The influence of α-amanitin on nucleolar and nucleoplasmatic RNA-synthesis is investigated autoradiographically. Amanitin inhibits the incorporation of uridine into the nucleoplasmatic RNA, whereas incorporation into the RNA of nucleoli is hardly or not at all influenced.We conclude that, in agreement with findings on animal cells, α-amanitin inhibits at least one of the RNA-polymerases localized in the nucleoplasm but does not markedly influence the RNA-polymerase of the nucleoli.