Haplotype tests using coalescent simulations conditional on the number of segregating sites.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
S Mousset
Publications and source records attributed to S Mousset.
Selective sweep near the In(2L)t inversion breakpoint in an African population of Drosophila melanogaster.
Chromosomal inversions largely inhibit recombination and may be associated with selective forces, such as hitch-hiking effects: the effect of positive selection on linked loci. A West African population of Drosophila melanogaster showed a high frequency (0.61) of the In(2L)t inversion. Departure from neutrality statistically associated with the inversion polymorphism was previously recorded at Su(H), a locus distant from the proximal breakpoint of the inversion. These results were consistent with hitch-hiking effects with recombination. The present sequence polymorphism survey involves a 1 kb fragment of the Vha68-1 locus located closer to the proximal breakpoint of the inversion. It shows a significant deficit of polymorphism with respect to divergence when compared with other loci studied in the same population, thus suggesting selective effects. Only 11 polymorphic sites are present in a sample of 20 chromosomes and these sites present a significant excess of rare-frequency variants. The major haplotype shows an unexpectedly high frequency. Our estimate of the background selection effect is not sufficient to account for the observed reduction of polymorphism. Intraspecific variation is structured between inverted and standard chromosomes; there are no shared polymorphisms but also no fixed differences between them. This pattern, together with that found on other loci previously studied near this inversion breakpoint, suggests hitch-hiking effects enhanced by the inversion.
Animals↗
Gene flow in a facultative apomictic poacea, the savanna grass Hyparrhenia diplandra.
The genetics of the poacea Hyparrhenia diplandra was studied in four natural populations from an ecological station in West Africa, where it makes up 80% of grasses from wet savanna and constitutes a dense continuum of randomly distributed individuals. DNA content and cytogenetical observations suggest it is an allotetraploid. Using two highly variable microsatellites (heterozygosity H = 0.615-0.616), we show that this species is an apomict with rare sexual reproduction events that account for approximately 0.5% of seeds pollinated in the wild. Hexaploid individuals were also produced, corroborating the observation of aberrant genotypes in the wild. The spatial extent of asexual clones in the field was low in comparison with the predominance of apomixis, thus indicating a low dispersal of seeds from their parent. Heterozygosity and departure from Hardy-Weinberg predictions were similar in the four populations, revealing a high apparent selfing rate s = 0.599 among sexually produced seeds. This is an overestimate since we could not distinguish true selfing from reciprocal outcrosses between neighboring individuals from the same apomictic clone. Gene flow by pollen could be substantial, possibly explaining the absence of isolation by distance in the studied area.
Africa, Western↗
p53-independent apoptosis and p53-dependent block of DNA rereplication following mitotic spindle inhibition in human cells.
We have studied the response of human transformed cells to mitotic spindle inhibition. Two paired cell lines, K562 and its parvovirus-resistant KS derivative clone, respectively nonexpressing and expressing p53, were continuously exposed to nocodazole. Apoptotic cells were observed in both lines, indicating that mitotic spindle impairment induced p53-independent apoptosis. After a transient mitotic delay, both cell lines exited mitosis, as revealed by flow-cytometric determination of MPM2 antigen and cyclin B1 expression, coupled to cytogenetic analysis of sister centromere separation. Both cell lines exited mitosis without chromatid segregation. K562 p53-deficient cells further resumed DNA synthesis, giving rise to cells with a DNA content above 4C, and reentered a polyploid cycle. In contrast, KS cells underwent a subsequent G1 arrest in the tetraploid state. Thus, G1 arrest in tetraploid cells requires p53 function in the rereplication checkpoint which prevents the G1/S transition following aberrant mitosis; in contrast, p53 expression is dispensable for triggering the apoptotic response in the absence of mitotic spindle.
Apoptosis↗
Cysteine control over glutathione homeostasis in Chinese hamster fibroblasts overexpressing a gamma-glutamylcysteine synthetase activity.
Gamma-glutamylcysteine synthetase (GCS) catalyses the first step of glutathione (GSH) biosynthesis and is considered to be the rate-limiting step of this pathway. In several experimental systems, GCS overexpression has been associated with GSH pool expansion and drug resistance. In this report, we describe a mutant line of Chinese hamster fibroblasts that overexpress this activity by 4-5 times, due to the amplification of the gene encoding the catalytic subunit of GCS. These mutant cells contained a wild-type steady-state level of GSH and, after depletion, synthesized GSH at the same rate as wild-type cells because their rate of endogenous production of cysteine was limiting. An exogenous supply of cysteine expanded the pool of GSH in mutant cells by 80% but did not increase that of wild-type cells, and, in GSH-depleted cells, increased the rate of GSH biosynthesis by eight and 35-times in wild-type and mutant cells, respectively. These experiments indicated that GCS overexpression had no consequence on the metabolism of GSH, unless a supply of cysteine was provided. Mutant cells were not resistant to cisplatin or nitrogen mustard.
Animals↗
Genistein analogues: effects on epidermal growth factor receptor tyrosine kinase and on stress-activated pathways.
Two genistein analogues (MD831 and MD833) have been synthesized and analyzed for their biological properties and their mechanism of action im comparison to genistein either in vitro or in intact cells. We showed that, in vitro, one of these compounds (MD831) inhibits the tyrosine kinase activity associated with the epidermal growth factor receptor (EGFR) as efficiently as genistein. However, treatment of A431 cells with these compounds did not result in any significant modification of EGFR tyrosine phosphorylation. Extracellular-signal regulated kinase (ERK) phosphorylation in cells stimulated by EGF was enhanced in the presence of MD831, whereas the other compounds, genistein and MD833, were able to activate the c-jun N-terminal kinase (JNK). This study showed that two structurally related compounds could elicit markedly different pharmacological effects on two signalling pathways, one involved in the mitogenic response and the other in the stress response. Such compounds may be useful to characterize signalling events involved in cell response to physiological stimuli.
Calcium-Calmodulin-Dependent Protein Kinases↗
The cytotoxicity of the parvovirus minute virus of mice nonstructural protein NS1 is related to changes in the synthesis and phosphorylation of cell proteins.
Autonomous parvoviruses exert lytic and cytostatic effects believed to contribute to their antineoplastic activity. Studies with inducible clones have demonstrated a direct involvement of parvovirus nonstructural proteins (NS) in oncolysis. Human and rat fibroblasts have been stably transfected with MVM(p) (minute virus of mice prototype strain) NS genes cloned under the control of a hormone-inducible promoter. Dexamethasone-induced synthesis of the NS proteins in sensitive transformed cells results in cell killing within a few days. From these sensitive cell lines have been isolated some NS-resistant clones that also prove resistant to MVM(p) infection, suggesting that cell factors modulate NS cytotoxicity. We have previously reported that factors involved in cell cycle regulation may contribute to this modulation, since NS toxicity requires cell proliferation and correlates with a cell cycle perturbation leading to an arrest in phase S/G2. In addition to its role in cytotoxicity, NS1 can regulate transcription driven by parvovirus and nonparvovirus promoters. Since phosphorylation is a critical event in controlling the activity of many proteins, notably transcription factors and cell cycle-regulated proteins, we have examined the effect of NS1 on the synthesis and phosphorylation of cell proteins. Our results indicate that NS1 interferes, within 7 h of induction, with phosphorylation of a protein of about 14 kDa (p14). Cell synchronization has enabled us to show that phosphorylation of this protein occurs in early S phase and is prevented when NS1 is induced. This early effect of NS1 on p14 phosphorylation may be directly linked to cytotoxicity and is probably related to the previously reported inhibition of cell DNA synthesis. Late in the induction period (24 h), NS1 also alters the synthesis of a 50-kDa protein and a 35-kDa protein (p50 and p35, respectively). Microsequencing of p35 reveals sequence homology with beta-tubulin. These effects of NS1, observed only in NS1-sensitive cell lines, may be related to the protein's cytotoxicity.
Amino Acid Sequence↗
The nonstructural proteins of the autonomous parvovirus minute virus of mice interfere with the cell cycle, inducing accumulation in G2.
The nonstructural (NS) proteins of the autonomous parvovirus minute virus of mice (prototype strain) are involved in viral DNA replication and in the regulation of parvoviral and heterologous promoters. By constructing cell lines having integrated the NS coding sequence under the control of an inducible promoter, we were able to demonstrate that NS proteins are toxic, once expressed in the transformed cells. Cell killing appears after several days of NS expression, suggesting that NS toxicity involved cellular factors. In this paper, we show that NS proteins are cytotoxic and interfere with the cell cycle in proliferating cells only NS expression is innocuous in resting cells, whereas in growing cells, it induces the accumulation of G2 cells. This cytostatic effect is enhanced upon neoplastic transformation, which sensitized the cells to NS killing. Moreover, as clones resistant to NS toxicity undergo no alteration of their cycle, this cytostatic effect of NS proteins could be an early step on the way to cell killing. These observations strongly suggest that NS toxicity involves cellular factors associated with the regulation of the cell cycle.
Animals↗
Activation of the mitogen-activated protein kinase cascade by tyrphostin (RG 50864).
Tyrphostins are synthetic compounds which have been described as in vitro inhibitors of epidermal growth factor (EGF)-receptor tyrosine kinase activity. In NIH3T3 cells, stimulation of EGF-receptor tyrosine kinase leads to an increase of intracellular protein phosphorylations, among them the phosphorylation of mitogen-activated protein (MAP) kinase and the S6 kinases p90rsk and p70S6K. Phosphorylation of these proteins, either on tyrosine or serine/threonine residues or on both residues increases their protein kinase activity. Unexpectedly, treatment of NIH3T3 cells with both tyrphostin (RG 50864) and EGF results in an increase in the level of tyrosine phosphorylation of the MAP kinase. During this treatment, we also observed an increase in MAP kinase and S6 kinase p90rsk activities. Tyrphostin treatment diminishes the level of c-fos mRNA but has no effect on c-myc mRNA expression nor on S6 kinase p70S6K activity. Mitogenic signalling induced by EGF in NIH3T3 cells was blocked by tyrphostin, suggesting that the target(s) for this event may be elements downstream from the MAP kinase or independent of this signal transduction.
3T3 Cells↗
The cytotoxicity of the autonomous parvovirus minute virus of mice nonstructural proteins in FR3T3 rat cells depends on oncogene expression.
The nonstructural (NS) proteins of the autonomous parvovirus minute virus of mice are involved in viral DNA replication and in the regulation of homologous and heterologous promoters. Moreover, NS products have proved to be cytotoxic, especially for transformed cells. We show here that intracellular accumulation of NS products is not sufficient to kill rat fibroblasts from the established cell line FR3T3, which is phenotypically normal in several respects. FRNS cell lines were obtained by stable transfection of FR3T3 cells by a vector carrying the NS genes under the control of the hormone-inducible long terminal repeat promoter of the mouse mammary tumor virus. In the presence of dexamethasone, the NS proteins were synthesized without associated cell death. Transformation of FRNS cells with the c-Ha-ras oncogene or polyomavirus oncogenes had little effect on their capacity for NS induction, as measured at both concentration and transactivating activity levels, yet the transformants were now dying within a few days in the presence of the inducer. The same results were obtained with cells stably transfected by a vector expressing the NS1 product alone, suggesting that in this system there is no cooperation between NS1 and NS2 for maximal cytopathic effect. Cell mortality after NS protein induction was quantitatively related to the yield of oncogene expression, while NS-1 was not limiting in this respect. Our results show that the NS1 protein is not lethal unless cellular factors that may depend on oncogene expression trigger its cytotoxicity.
Animals↗
Cooperation of oncogenes in cell transformation and sensitization to killing by the parvovirus minute virus of mice.
The established line of normal Fisher rat fibroblasts (FR3T3) is naturally resistant to the parvovirus minute virus of mice (MVM), and was used as a model system to study the influence of stepwise transformation on the susceptibility of cells to this virus. When transformed with genes encoding the class I nuclear oncoproteins large T antigen of polyomavirus (PyLT) or v-myc, cells retained a normal appearance, but acquired some ability to form colonies in soft agar. On the other hand, the class II transforming oncogenes encoding the middle T antigen of polyomavirus (PyMT) and c-Ha-ras-1 induced both morphological alterations and a high capacity for anchorage-independent growth in transfected cells. The concomitant expression of oncogenes from both classes (PyLT-(+)PyMT; v-myc+c-Ha-ras-1) induced a supertransformed phenotype characterized by the piling-up of cells into poorly adherent foci, even in low density cultures. The progressive transformation of this cellular system was found to coincide with a gradual increase in its susceptibility to MVMp (MVM prototype strain) infection. Compared to parental cells, class I, class II and double transformants proved to be sensitized to killing by MVMp to a low, moderate and large extent, respectively. Thus, oncogenes from different functional classes appeared to cooperate in the responsiveness of cells to parvovirus attack. Interestingly, this cooperation exacerbated both the killing of infected cells and their capacity to produce viral non-structural (NS) proteins, in agreement with the reported cytotoxic activity of NS polypeptides. Therefore, in this system, parameters of the parvovirus life cycle may serve as indications of the overall progression of the transformation process.
Animals↗
Early effect of BCNU on rat astrocytes. Inhibition of S6 kinase activation by growth factors.
In primary cultures of astrocytes, methylmethane, 2-N-methyl 9-hydroxy-ellepticinium acetate, ditercalinium, 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea and 1,3 bis (2-chloroethyl)-1-nitrosourea (BCNU) blocked to various extents the activation of S6 kinase by acidic fibroblast growth factor and insulin [or insulin-like growth factor 1 (IGF1)]. The effects of the most active agent, BCNU, were time and concentration dependent. Pretreatment of cells with 50 microM BCNU for 1 hr completely prevented S6 kinase activation by growth factors for at least 2 days. The S6 kinase activity of unstimulated cells was slightly affected. S6 kinase activation by 12-O-tetradecanoylphorbol 13 acetate was also strongly impaired by treating cells with BCNU whereas activation by 8-bromo-cyclic AMP was slightly reduced. Cyclic AMP-dependent protein kinase and phospholipid and Ca(2+)-dependent protein kinase were unaffected. BCNU had no direct effect on IGF1 binding to cell surface receptors or on the S6 kinase activity of cell cytosols.
Animals↗
Selective killing of transformed rat cells by minute virus of mice does not require infectious virus production.
Fischer rat fibroblasts, naturally resistant to killing by the fibrotropic strain of minute virus of mice [(parvovirus MVM(p)], became sensitive to MVM when transformed by polyomavirus. This sensitization did not involve an increase in the percentage of cells which synthesized viral capsid antigens or in the percentage of cells which produced infectious virus. The addition of anti-MVM antiserum to the growth medium of MVM-infected cells had only a small effect on their survival rates, indicating that the majority of the killing effect of MVM occurs in a single cycle of infection. The data indicate that cell killing by MVM is independent of infectious virus production and thus support the notion that the preferential cytolytic effect is affected by viral cytotoxic gene products which accumulate to intolerable levels in transformed cells but not in normal ones. Finally, using cells transformed with polyomavirus and genomic and subgenomic clones of polyomavirus, we showed that the extent of sensitization to killing by MVM depended on the transforming agent used.
Animals↗
Susceptibility to parvovirus Minute virus of mice as a function of the degree of host cell transformation: little effect of simian virus 40 infection and phorbol ester treatment.
Transformation of mouse fibroblasts by simian virus 40 (SV40) or certain oncogenes enhances their susceptibility to the lytic replication of Minute virus of mice (MVM), a non-defective parvovirus. It was investigated whether this cytotoxic action of MVM can also be potentiated by two types of incomplete and reversible cell transformation induced either by SV40 infection or by exposure to the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Although the latter two treatments trigger the expression of several traits of the transformed phenotype, they do not significantly enhance cell permissiveness to MVM.
Animals↗
Genotoxicity of ochratoxin A in mice: DNA single-strand break evaluation in spleen, liver and kidney.
Ochratoxin A, a natural contaminant of feed and food, has been shown to induce experimental liver and kidney tumours. In vitro experiments on mice spleen cells showed evidence of DNA single-strand breaks induced by ochratoxin A. We measured single-strand breaks in the DNA of spleen, liver and kidney of ochratoxin A-treated animals. Ochratoxin A induced DNA damage in vivo. This damage reversed with time. The appearance and extent of the damage varied in different tissues. Except for spleen our data correlate with the tumours induced by ochratoxin in mouse liver and kidney. With regard to the spleen, there has been no report to date of experimental leukemia induced by ochratoxin A. Thus our results indicate that this possibility has to be considered.
Animals↗
A study of intermediate filaments (cytokeratin, vimentin, neurofilament) in two cases of Merkel cell tumor.
In two cases of Merkel cell tumor, the study of intermediate filaments, using monoclonal antibodies (vimentin, cytokeratin, neurofilaments), confirmed the double differentiation (neuroendocrine and epithelial) of this tumor as previously observed in histological, electron microscopical and histochemical analyses. Labelling of the tumor cells was positive with monoclonal antibodies against neurofilament proteins and cytokeratin.
Adenocarcinoma↗
[DNA damage in the spleen, liver and kidneys of mice treated with ochratoxin A].
Ochratoxin A a natural contaminant of feed and food has been shown to induce experimental liver and kidney tumors. Since there is a good correlation between the carcinogenic potency of chemicals and the DNA damages induced in mammalian cells treated either in vivo or in vitro by these compounds, we have measured single-strand breaks induced by ochratoxin A in DNA of liver, spleen and kidney. Our data clearly showed that ochratoxin A induced DNA damages in vitro as well as in vivo. Damages were dose-dependent, reversible and vary upon the time according to the tissue. In spite there is no report up to now on experimental leukemia induced by ochratoxin A, our results indicate that this possibility have to be considered.
Animals↗
[Chloracne caused by manipulation of herbicides].
Explore the source record for details and available documents.
Acne Vulgaris↗