Studies of mitotic and centromeric abnormalities in Roberts syndrome: Implications for a defect in the mitotic mechanism

Roberts syndrome is an inherited human condition that is of particular interest because separation of centromeres and constitutive heterochromatin is observed in metaphase chromosomes. In this study we investigated the frequency of other cytological abnormalities in three Roberts syndrome patients. Our findings when taken with previous cytological reports emphasize that there are other features that are equally characteristic of Roberts syndrome: (1) aneuploidy with random chromosome loss and (2) micronuclei and/or nuclear lobulations of 8%–24% of interphase cells. We observed abnormal chromosome movement involving one or all the chromosomes during anaphase. Evidence is presented suggesting that aneuploidy, micronuclei and abnormal nuclear morphology are a direct result of lagging chromosomes. The cytological features documented for Roberts syndrome indicate that this is a human mitotic mutant.by T.C. Hsu     

Endopolyploidy in irradiated p53-deficient tumour cell lines: persistence of cell division activity in giant cells expressing Aurora-B kinase

Recent findings including computerised live imaging suggest that polyploidy cells transiently emerging after severe genotoxic stress (and named 'endopolyploid cells') may have a role in tumour regrowth after anti-cancer treatment. Until now, mostly the factors enabling metaphase were studied in them. Here we investigate the mitotic activities and the role of Aurora-B, in view of potential depolyploidisation of these cells, because Aurora-B kinase is responsible for coordination and completion of mitosis. We observed that endopolyploid giant cells are formed via different means in irradiated p53 tumours, by: (1) division/fusion of daughter cells creating early multi-nucleated cells; (2) asynchronous division/fusion of sub-nuclei of these multi-nucleated cells; (3) a series of polyploidising mitoses reverting replicative interphase from aborted metaphase and forming giant cells with a single nucleus; (4) micronucleation of arrested metaphases enclosing genome fragments; or (5) incomplete division in the multi-polar mitoses forming late multi-nucleated giant cells. We also observed that these activities can release para-diploid cells, although infrequently. While apoptosis typically occurs after a substantial delay in these cells, we also found that approximately 2% of the endopolyploid cells evade apoptosis and senescence arrest and continue some form of mitotic activity. We describe here that catalytically active Aurora-B kinase is expressed in the nuclei of many endopolyploid cells in interphase, as well as being present at the centromeres, mitotic spindle and cleavage furrow during their attempted mitotes. The totally micronucleated giant cells (containing sub-genomic fragments in multiple micronuclei) represented only the minor fraction which failed to undergo mitosis, and Aurora-B was absent from it. These observations suggest that most endopolyploid tumour cells are not reproductively inert and that Aurora-B may contribute to the establishment of resistant tumours post-irradiation.     

Nature of antigens and antibodies in immune complexes isolated by staphylococcal protein A from plasma of melanoma patients

Summary Immune complexes (IC) were isolated from plasma of melanoma patients by absorption to staphylococcal protein A and subsequent elution with MgCl₂. The isolated ICs were purified by precipitation with polyethylene glycol and sucrose density gradient ultracentrifugation after radioiodination with ¹²⁵I. The purified ICs were dissociated and radiolabeled antigen/antibody components were separated by ultracentrifugation at low pH (2.6). Under these conditions, about 72% radioactivity of the purified IC remained in the light-density region as a wide band. After neutralization, 26%–60% radioactivity in the region of 5S sedimentation bound to immobilized autologous immunoglobulins, as opposed to a maximum of 23% to immobilized immunoglobulins from human normal serum. Significant levels (73%–77%) of radioactivity in 7S region bound to rabbit anti-human IgG immunobeads. Immunoprecipitation of the antigen fraction by allogeneic anti-melanoma and rabbit anti-melanoma antibodies followed by SDS-polyacrylamide gel electrophoresis revealed the presence of a fetal antigen (FA) and a melanoma tumor-associated antigen (TAA). In addition, the presence of auto-antigen(s) was indicated by using autologous antibody in immunoprecipitation. Immunoglobulins (IgG) isolated from purified IC bound to cultured melanoma, sarcoma, and normal fibroblasts, although the binding to sarcoma and normal fibroblasts could be inhibited by preincubation of isolated IgG with soluble FA but not with soluble melanoma TAA. Thus, results of this investigation provide evidence that circulating IC in melanoma patients are composed of at least IgG and different antigens, and some of these antigens are produced by their tumor.     

Mechanisms of tumour rejection in the murine DBA/2-SL2 concomitant immunity system

Summary The mechanisms of rejection of secondary tumours were studied in concomitant immunity using transplants of standard-size solid SL2 tumours in syngeneic DBA/2 mice. In such a system primary tumour implants are not rejected, in contrast to secondary tumour implants. The second tumour was mainly rejected 2–4 days after implantation. Both primary tumour and secondary tumour implants (which are rejected) contained hardly any lymphocyte infiltrate, whereas, 2–4 days after implantation they contained 40%–50% macrophages, which were cytotoxic in vitro. Transfer (s.c.) of these tumours to naive mice showed that cellular infiltrates in the secondary implants did not always cause tumour rejection. Serum collected on day 4 after implantation of the secondary tumour was cytotoxic to SL2 tumour cells in vitro, whereas serum from mice with only primary implants was not cytotoxic on day 4 after implantation. Preliminary characterization of this cytotoxic factor showed that it was heat-labile, as cytotoxicity disappeared after 30 min at 56°C, the molecular mass of the factor was higher than 100 kDa, and it was not IgG. We hypothesize that secondary tumours in the DBA/2-SL2 concomitant immunity system are rejected mainly between 2 and 4 days after implantation as a result of the combined action of cytotoxic serum and the presence of 40%–50% cytotoxic macrophages. The primary tumour is not rejected at 2–4 days after implantation as there is no cytotoxic factor.     

Cross-reactivity of lung cancer patients' leucocytes in the leucocyte migration inhibition test

Summary Panels of 3 M KCl extracts of squamous-cell carcinomas, adenocarcinomas and oat-cell carcinomas of the lung were used for a comprehensive analysis of cross-reactivity in the leucocyte migration test. Lung cancer patients' leucocytes showed positive reactivity in 69%–100% of cases (n=353). No significant differences were observed when data were grouped with respect to the histological type of the tumours used for extraction or of the tumours of the leukocyte donors. Leukocytes of patients bearing tumours of nonpulmonary origin exposed to lung cancer extract panels and leukocytes of lung cancer patients exposed to gastrointestinal cancer extract panels were definitely less reactive (35%–47% and 6%–38%, respectively). However, a high reaction frequency was found in patients with lung metastases from different nonpulmonary tumours. This group of patients also frequently showed reactivity (52%) with normal lung tissue extracts. Patients with benign lung diseases reacted positively with lung tumour extracts in 25%–39% of cases, but donors with other benign disease and healthy controls were virtually nonreactive (0–14%).Hence, a high degree of cross-reactivity occurs in the lung cancer system and restricted cross-reactivity occurs with tumours of other organs. Possible explanations for the lung-oriented reactivity of patients with lung metastases are discussed.Abbreviations LMI leucocyte migration inhibition - MI migration index - LMT leucocyte migration test - SCC squamous-cell carcinoma - OCC oat-cell carcinoma - AC adenocarcinoma     

Analysis of germinal aging in Paramecium caudatum by micronuclear transplantation

The role of the micronucleus in the age-dependent increase in mortality after conjugation in Paramecium has been investigated using micronuclear transplantation. The clone of Paramecium caudatum used for this study had a lifespan of about 750 fissions. In this clone, the fission rate began to decrease about 450 fissions after conjugation. Mortality after selfing conjugation also began to appear at about 450 fissions and gradually increased with clonal age. Cells at about 650 fissions showed 10–70% survival after selfing conjugation but when their micronuclei were transplanted into amicronucleate cells of about 450 fissions, the progeny survival increased to 70–90%. When micronuclei from cells 700–750 fissions old were transplanted into amicronucleate cells of 100–150 fissions, however, increase in progeny survival was very rare. The results indicate that micronuclei in cells up to the age of 650 fissions can function normally if the cytoplasmic environment is young.     

Genotoxicity of five food preservatives tested on root tips of Allium cepa L

The effects of the food preservatives sodium benzoate (SB), boric acid (BA), citric acid (CA), potassium citrate (PC) and sodium citrate (SC) have been studied on root tips of Allium cepa L. Roots of A. cepa were treated with a series of concentrations, ranging from 20 to 100 ppm for 5, 10 and 20 h. The results indicate that these food preservatives reduced mitotic division in A. cepa compared with the respective control. Mitotic index values were generally decreased with increasing concentrations and longer treatment times. Additionally, variations in the percentage of mitotic stages were observed. The total percentage of aberrations generally increased with increasing concentrations of these chemicals and the longer period of treatment. Different abnormal mitotic figures were observed in all mitotic phases. Among these abnormalities were anaphase bridges, C-mitosis, micronuclei, lagging, stickiness, breaks and unequal distribution.     

Genotoxicity of five food preservatives tested on root tips of Allium cepa L.

The effects of the food preservatives sodium benzoate (SB), boric acid (BA), citric acid (CA), potassium citrate (PC) and sodium citrate (SC) have been studied on root tips of Allium cepa L. Roots of A. cepa were treated with a series of concentrations, ranging from 20 to 100 ppm for 5, 10 and 20 h. The results indicate that these food preservatives reduced mitotic division in A. cepa compared with the respective control. Mitotic index values were generally decreased with increasing concentrations and longer treatment times. Additionally, variations in the percentage of mitotic stages were observed. The total percentage of aberrations generally increased with increasing concentrations of these chemicals and the longer period of treatment. Different abnormal mitotic figures were observed in all mitotic phases. Among these abnormalities were anaphase bridges, C-mitosis, micronuclei, lagging, stickiness, breaks and unequal distiribution.     

The effect of hyperthermia on micronucleus induction by mutagens in mice

We administered mitomycin C (0.5 mg/kg) intraperitoneally to hyperthermic-treated mice and examined the effect of hyperthermia on micronucleus induction. Hyperthermia enhanced micronucleus induction. The timing of chemical administration relative to the start of hyperthermic treatment (37°C ambient temperature) influenced micronucleus frequency, and the effect was greatest 2 h after the start of hyperthermic treatment. But the hyperthermic treatment did not change the time course of micronucleus induction. In addition, we investigated the effect of hyperthermia on micronucleus induction by chemicals with different modes of action, i.e., alkylating agents (mitomycin C at 0.1–0.5 mg/kg, cyclophosphamide at 1.25–10 mg/kg), a spindle poison (colchicine at 0.05–1.0 mg/kg), and an antimetabolite (5-fluorouracil at 2.5–50 mg/kg). Hyperthermia enhanced only the clastogenicity of alkylating agents.     

Indomethacin inhibits cell proliferation in the oxyntic epithelium of the rat

The aim of this investigation was to examine the action of parenteral indomethacin and oral prostaglandin E₂ on cell proliferation in the rat oxyntic mucosa. Groups of Sprague Dawley rats were treated with either 1.5 mg/kg indomethacin subcutaneously, 5 mg/kg oral prostaglandin E₂ or placebo, twice daily during 5 days. All rats were killed exactly 4 hours after mitotic arrest with vincristine, and a biopsy specimen from the oxyntic mucosa was processed for routine microscopic evaluation.Mitotic figures were distributed cluster-like along the oxyntic mucosa alternating with mitosis-free areas. The total number of mitotic figures in 8 mm of mucosa was significantly reduced by administration of indomethacin (p<0.05). In rats given indomethacin, 32.5% of the examined mucosa did not have mitotic figures, which is significantly higher than 14.3% as observed in placebo-treated rats (p<0.05). Both rats treated with indomethacin and with prostaglandin E₂ had fewer microscopic fields containing 5–6 mitotic figures than placebo-treated animals (p<0.05). The maximal length of mitosis-free areas was 0.6 (0.6–0.9) mm in rats given indomethacin which is significantly larger than 0.4 (0.2–0.4) mm observed in controls (p<0.05). Indomethacin produced epithelial atrophy as shown by a significant reduction of the epithelial height observed in those rats compared to controls (p<0.05).The inhibition of cell proliferation observed in the oxyntic mucosa of rats treated with the cyclooxygenase blocker indicates that an important physiological role of endogenous prostaglandin is to maintain the proliferative activity of the epithelium at a high level.     

Cremart: A new chemical for efficient induction of micronuclei in cells and protoplasts for partial genome transfer

Summary Results on efficient induction of micronuclei by Cremart in suspension cells and protoplasts of potato are reported. Cremart is a highly effective phosphoric amide herbicide, which acts on the mitotic spindle, and induces micronuclei through modification of mitosis. After treatment with Cremart, metaphase chromosomes changed directly into micronuclei without centromere division and chromatid separation. When suspension cells were treated with Cremart (3.7–15.0 M) for 48h, and subsequently incubated in a mixture of cell wall-digesting enzymes in the presence of cytochalasin-B and Cremart for 18h, the frequency of micronucleation in the cell/protoplast mixture increased significantly, as compared to that obtained after treatment of suspension cells with Cremart (3.7–15.0 M) for 48 h. Sieving after enzyme incubation resulted in the recovery of protoplasts, showing mass induction of micronuclei. Also synchronized suspension cells of Nicotiana plumbaginifolia responded with high frequency of micronucleation after Cremart (3.7 M) treatment. The application of this procedure for partial genome transfer is discussed.Abbreviations APM Amiprophos-methyl - BAP 6-Benzyl aminopurine - CB Cytochalasin-B - MI Mitotic index - MN Micronuclei - MS Murashige and Skoog - NAA 1-Naphthalene acetic acid     

The membranes of slowly drought-stressed wheat seedlings: a freeze-fracture study

Seedlings of Triticum aestivum L. cv. Neepawa were slowly drought-stressed by witholding water after sowing in pots. Leaf extension stopped during development of the third leaf. Damage was assessed by rewatering the pots and measuring regrowth; 1–5 d after growth stopped, rewatering induced significant regrowth within several hours; 6–13 d after growth stopped, regrowth was delayed; from 14 d after growth stopped, no regrowth occurred after rewatering. Leaf bases were excised from the drought-stressed seedlings during this period of increasing damage, and were freeze-etched.Intramembranous particles (IMP) were evenly scattered in the plasma membrane in those plants which regrew immediately after rewatering. In the plants which regrew after a delay or which did not regrow on rewatering, there were patches without IMP in plasma membrane, nuclear envelope, and other membranes. Plasma membrane, nuclear envelope and possibly other membranes were sometimes partly replaced by vesicles, possibly formed from the original membrane. Such vesiculation occurred in a few cells in plants which survived the stress with a delayed regrowth, and was commoner in the plants which did not recover. The results support the idea that slow drought induces IMP-free patches in membranes including the plasma membrane, this induces membrane reorganisation including vesiculation of membranes and coagulation of protoplasm, and that these are expressed as delayed or failed regrowth. Some IMP-free patches in the plasma membrane had a faint ordered sub-structure, possibly a hexagonal lipid phase. Such patches were infrequent and IMP sometimes occurred in areas of plasma membrane having an apparently similar sub-structure. Thus the IMP-free patches could not be explained by a lamellar-hexagonal phase transition. As the stress became damaging, vesicles and endoplasmic reticulum accumulated immediately next to the plasma membrane. Mainly during the early period of damaging stress (6–10 d after growth stopped), depressions, invaginations, and rarer lesions occurred in the plasma membrane, sometimes associated with some of the IMP-free patches. In the same period, many nuclear envelopes had exceptionally large nuclear pores.Abbreviations E exoplasmic - IMP intramembranous particles - P protoplasmic     

Endophytic fungi (Neotyphodium coenophialum) affect the growth and mineral uptake, transport and efficiency ratios in tall fescue (Festuca arundinacea)

Neotyphodium coenophialuminteracts mutualistically with its host grasses. Tall fescue (Festuca arundinacea Schreb.) plants infected by the fungal endophyte,Neotyphodium coenophialum(Morgan-Jones and Gams) Glenn, Bacon and Hanlin, often perform better than non-infected plants, especially in limited resource environments. However, there is a scarcity of information about endophyte-grass ecotypes interaction in Andisols of temperate regions. Clones of three tall fescue ecotypes (Fukaura, Koiwai and Showa) either infected with N. coenophialum (E+) or noninfected (E–) were grown in Andisols (Black Andisol: naturally low content of phosphorus, high in other nutrients; Red Andisol: naturally high content of phosphorus, low in other nutrients) for 133 days in a controlled environment. Cumulative shoot dry weight, daily regrowth rates (tiller number, plant height and shoot dry matter) after clippings and nutrient uptake, transport and efficiency ratios were measured. In Black Andisol, E+ plants had significantly higher cumulative shoot dry weight as well as daily regrowth rates than E– plants, while in Red Andisol the reverse was true. Among the ecotypes studied, Showa had the highest shoot growth. Significantly higher phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) uptake as well as transport were identified in E+ vs. E– plants grown in Black Andisol. With few exceptions, values for nutrient efficiency ratios were not significantly different between E+ and E– plants grown in both soils. Significant three-way interaction (endophyte × ecotype × soil) for cumulative shoot dry weight and regrowth rate revealed that the ecotype specific regrowth responses to endophyte infection were depended on soil nutrient conditions. Vegetative growth and nutrient acquisition in tall fescue varied with ecotype and were modified by abiotic (soil fertility status) as well as biotic (endophyte infection) factors.     

Activation markers on T cells infiltrating melanoma metastases after therapy with dinitrophenyl-conjugated vaccine

Treatment of metastatic melanoma patients with an autologous vaccine modified by the hapten, dinitrophenyl (DNP), produces a striking immunological effect: the induction of clinically evident inflammatory responses in metastatic tumors. Histological examination shows these tumors to be infiltrated with T lymphocytes. We studied the expression of activation markers on those cells and compared them with matched peripheral blood lymphocytes (PBL) and with lymphocytes extracted from metastases before treatment with DNP-conjugated vaccine. The median fraction of cells that were T cells in post-vaccine tumors was 41%, as compared with 9% in pre-treatment tumors, and those T cells were predominantly CD8⁺ (mean CD8/CD4 ratio=5.0). A high proportion of both pre- and posttreatment infiltrating T cells expressed HLA-DR (mean±SE=48%±4%), CD69 (56%±7%), and ganglioside GD3 (68%±5%). This distinguished them from matched PBL in which expression of those markers was significantly lower (HLA-DR=10%±2%; CD69=2%±0.4%; GD3=49%±4%). These changes were not accompanied by increased cell-surface expression of interleukin-2 (IL-2) receptors, either CD25 or p75, which were expressed by 1%–2% and 12% of tumor-infiltrating lymphocytes (TIL), respectively. The pattern of activation marker expression that we identified appears to be characteristic of tissue T cells with the memory phenotype. The low expression of IL-2 receptors could indicate functional impairment of TIL in situ, perhaps because of inhibitory molecules produced by melanoma cells.This work was supported by NIH grants CA 39248, CA 40358, and AR 39674 from the National Institutes of Health and by funds from the Nat Pincus Trust     

Subcellular distribution of glycoside hydrolase and polysaccharide depolymerase enzymes in the rumen entodiniomorphid ciliatePolyplastron multivesiculatum

The distribution of 12 acid hydrolase and two polysaccharide depolymerase enzymes in the rumen entodiniomorphid ciliatePolyplastron multivesiculatum, isolated from the ovine rumen 2 h after feeding, was examined by differential and density-gradient centrifugation. Approximately 60%–70% of the recovered activity was sedimentable in fractions prepared by centrifugation at 10³ g for 10 min (F1) and 10⁴ g for 10 min (F2) with 25%–35% of the acid hydrolases and 15%–20% of acid phosphatase and the polysaccharidases remaining nonsedimentable (in fraction F5) after centrifugation at 10⁵ g for 60 min. Approximately 60% of the sedimentable activity was located in fraction F1. Latency of the hydrolase activity was demonstrated. After isopycnic centrifugation in sucrose density gradients, the hydrolytic enzymes cosedimented in acid phosphatase-containing, membrane-bound, pleomorphic lysosomelike vesicles 0.1–1.0 m in size, with a mean equilibrium density of 1.17 (1.15–1.19) g/ml.     

Major histocompatibility complex class II antigen expression during potentiation of line-10 tumor immunity after intralesional administration of bacillus Calmette-Guérin

Summary Intralesional injection of BCG into an established line-10 hepatocellular carcinoma in the strain-2 guinea pig causes regression of the tumor and induction of line-10 immunity. We found that the animals were already protected for a second challenge with line-10 tumor cells 7 days after BCG treatment. We studied whether this early induction of immunity was correlated with the expression of MHC class II antigens on line-10 tumor cells and was correlated with an increased expression of MHC class II antigens on leukocytes in the primary tumor and in the regional lymph node (Ln. axillaris accessorius). The MHC class II antigens and the leukocyte subpopulations were measured with monoclonal antibodies and flow cytofluorometry. In the draining lymph node the number of nucleated cells increased about 10-fold during the first 5 days after intralesional injection of BCG. At this time the MHC class II antigen expression of these cells was increased from 21%–32% in the naive controls to 39%–53% in animals with BCG-treated tumors. This implies that the number of MHC-class-II-positive cells increased about 20-fold in the draining lymph node. Surprisingly, the increase in percentage of MHC-class-II-antigen-positive cells was mainly due to an increase of IgM-positive B cells from 8%–11% to 22%–41% and an increase of IgG-positive B cells from 7%–27% to 25%–44%. In the tumor, BCG treatment induced a small increase of MHC-class-II-antigen-positive cells from 11%–12% to 15%–20%. Probably this increase came not from tumor cells but mainly from a BCG-induced infiltration of mononuclear cells, as an increase of T cells from 14% to 20%, an increase of macrophages from 8% to 18%, and an increase of B cells from 0 to 6% was observed. We conclude that the potentiation of anti-(line-10 tumor cell) immunity correlated with a 20-fold increase of MHC-class-II-antigen-positive cells in the lymph nodes and a small increase in the number of MHC-class-II-antigen-positive tumor-infiltrating cells.     

Wirkung von Endoxan auf die Chromosomen von HeLa-Zellen

Mutagenic effects induced by solutions of Cytoxan-Substance and its activated compound (rat-passage) are tested in He-La cells.Cytoxan-substance induces chromatid aberrations as well as mitotic depression 44–48 hs after treatment in proportion to the concentration. 22–24 hs after treatment no effects are seen. Activated Cytoxan induces gaps and breaks in HeLa cells harvested 22 hs after treatment. Reunion-figures are missing.Incubating cultures up to 46 hs after treatment leads to few gaps, more breaks and a high number of reunion-figures.It is not known if activated Cytoxan delays the cell cycle or single phases of the cycle. It is discussed that autoradiographic experiments are nessessary to get more information on sensitive and/or delayed phases of the cycle under influence of activated Cytoxan. Furthermore those studies have proved to be helpful to solve questions about the rejoining mechanism.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Physiological regeneration of the digestive parenchyma in Convoluta convoluta and Oxyposthia praedator (Turbellaria,Acoela)

Autoradiography has been applied to two acoel turbellarians, Convoluta convoluta and Oxyposthia praedator, to determine the distribution and fate of proliferative cells. In C. convoluta, mitotic figures and nuclei that labelled with [³H]thymidine could be observed in the peripheral parenchyma but not in the middle zone of the central parenchyma. The time required for regeneration of physiologically competent digestive cells was about 10–15 days. In O. praedator, mitotic figures (in metaphase and telophase) were observed in the peripheral parenchyma while none were found in the epidermis either in untreated animals or after treatment with colchicine. Mitotic figures were found only rarely in the central parenchyma and only in its marginal zone. Autoradiographs of O. praedator demonstrated [³H]thymidine incorporation into both the nuclei and the cytoplasm of peripheral parenchymal cells. In the central parenchyma, no nuclei with primary labelling were observed. The digestive parenchyma of the acoels is regarded as a unique histological system involving both specialized cells of the central parenchyma and stem cells located in the peripheral parenchyma.     

Cytogenetic effects of ribavirin on mouse bone marrow

The micronucleus test and mitotic chromosome analysis were used to study the in vivo mutagenic activity of ribavirin on bone marrow cells of Swiss albino mice. To determine the incidence of micronuclei, mice were injected i.p. twice, at an interval of 24 h. with the drug at doses of 20, 100 and 200 mg/kg. Animals were killed 6 h after the second dose and bone marrow was examined for the presence of micronuclei in developing erythrocytes. Ribavirin significantly (P less than 0.05) induced micronuclei in polychromatic erythrocytes at all doses. A study was conducted to investigate the cytogenetic effect of the drug on mitotic chromosomes. Ribavirin at 200 mg/kg/day was administered to mice for 3 and 5 days. Repeated treatment with the high dose of ribavirin produced a highly significant (P less than 0.02) increase in abnormal metaphase spreads. The results indicate that ribavirin is mutagenic to bone marrow cells of mice as evaluated by the micronucleus test and by chromosome analysis.     

Effects of deletions on mitotic stability of the Paternal-Sex-Ratio (PSR) chromosome from Nasonia

Paternal-Sex-Ratio (PSR) is a B chromosome that causes all-male offspring in the parasitoid wasp Nasonia vitripennis. It is only transmitted via sperm of carrier males and destroys the other paternal chromosomes during the first mitotic division of the fertilized egg. Because of haplodiploidy, the effect of PSR is to convert diploid (female) eggs into haploid eggs that develop into PSR-bearing males. The PSR chromosome was previously found to contain several families of repetitive DNA, which appear to be present in local blocks. PSR chromosomes with irradiation-induced deletions have decreased rates of transmission and increased variation in transmission. This study investigates whether these differences in transmission of deletion chromosomes are due to mitotic instability. Two deleton chromosomes (E306 and F316) and the wild-type PSR chromosome were examined. A cytogenetic assay of testes revealed that wild-type PSR males contained the chromosome in 98%–100% of their spermatocytes. Similar counts from carriers of two delection chromosomes were lower and varied between individuals from 50%–100%. One F316 male did not contain the chromosome in any of its spermatocytes although the chromosome was present in somatic tissues based on hybridization to PSR-specific repetitive DNA. A molecular analysis of males found the wild-type PSR chromosome to be present in all somatic tissues. Tissue specific differences in the presence of PSR were found in several males from the two deletion lines. The results show that deletions can result in mosaicism due to increased mitotic instability of PSR. Such individuals sometimes partially or completely fail to transmit the chromosome. Patterns of mosaicism of B chromosomes in other organisms are discussed.by P.B. Moens