Elasticity-based boosting of neuroepithelial nucleokinesis via indirect energy transfer from mother to daughter.

Neural progenitor cells (NPCs), which are apicobasally elongated and densely packed in the developing brain, systematically move their nuclei/somata in a cell cycle-dependent manner, called interkinetic nuclear migration (IKNM): apical during G2 and basal during G1. Although intracellular molecular mechanisms of individual IKNM have been explored, how heterogeneous IKNMs are collectively coordinated is unknown. Our quantitative cell-biological and in silico analyses revealed that tissue elasticity mechanically assists an initial step of basalward IKNM. When the soma of an M-phase progenitor cell rounds up using actomyosin within the subapical space, a microzone within 10 µm from the surface, which is compressed and elastic because of the apical surface's contractility, laterally pushes the densely neighboring processes of non-M-phase cells. The pressed processes then recoil centripetally and basally to propel the nuclei/somata of the progenitor's daughter cells. Thus, indirect neighbor-assisted transfer of mechanical energy from mother to daughter helps efficient brain development.

Toxicity of dihydroxyacetone is exerted through the formation of methylglyoxal in Saccharomyces cerevisiae: effects on actin polarity and nuclear division.

Dihydroxyacetone (DHA) is the smallest ketotriose, and it is utilized by many organisms as an energy source. However, at higher concentrations, DHA becomes toxic towards several organisms including the budding yeast Saccharomyces cerevisiae In the present study, we show that DHA toxicity is due to its spontaneous conversion to methylglyoxal (MG) within yeast cells. A mutant defective in MG-metabolizing enzymes (glo1Δgre2Δgre3Δ) exhibited higher susceptibility to DHA. Intracellular MG levels increased following the treatment of glo1Δgre2Δgre3Δ cells with DHA. We previously reported that MG depolarized the actin cytoskeleton and changed vacuolar morphology. We herein demonstrated the depolarization of actin and morphological changes in vacuoles following a treatment with DHA. Furthermore, we found that both MG and DHA caused the morphological change in nucleus, and inhibited the nuclear division. Our results suggest that the conversion of DHA to MG is a dominant contributor to its cytotoxicity.

Cytotoxicity and genotoxicity of clothianidin in human lymphocytes with or without metabolic activation system.

Clothianidin (CHN) is a broad-spectrum neonicotinoid insecticide. Limited studies have been carried out on the cytotoxic and genotoxic effects of both CHN using different genotoxicity tests in human cells with or without human metabolic activation system (S9 mix). Therefore, the aim of this study is to investigate the cytotoxic and genotoxic effects of CHN and its metabolites on human lymphocyte cultures with or without S9 mix using chromosomal aberration (CA) and micronucleus (MN) tests. The cultures were treated with 25, 50, and 100 µg/ml of CHN in the presence (3 h treatment) and absence (48 h treatment) of S9 mix. Dimethyl sulfoxide (DMSO) was used as a solvent control. CHN showed cytotoxic and genotoxic effects due to significant decreases in mitotic index (MI) and nuclear division index (NDI), and significant increases in the CAs, aberrant cells, and MN formation in the absence of S9 mix when compared with solvent control. However, CHN did not significantly induce cytotoxicity and genotoxicity in the presence of S9 mix. Our results indicated that CHN has cytotoxic, cytostatic, and genotoxic potential on human peripheral blood lymphocyte cultures, but not its metabolites under the experimental conditions.

Ziprasidone induces cytotoxicity and genotoxicity in human peripheral lymphocytes.

It has been stated that some antipsychotic drugs might cause genotoxic and carcinogenic effects. Ziprasidone (ZIP) is commonly used an antipsychotic drug. However, its genotoxicity and carcinogenicity data are very limited. The cytotoxicity and genotoxicity of ZIP on human peripheral blood lymphocytes were examined in vitro by sister chromatid exchange (SCE), chromosome aberration (CA) and micronucleus (MN) tests in this study. Lymphocyte cultures were treated with 50, 75 and 100 µg/ml of ZIP in the presence and absence of a metabolic activator (S9 mix). Dimethylsulfoxide was used as a solvent control. While the cells were treated with ZIP for 24 h and 48 h in cultures without S9 mix, the cultures with S9 mix were exposed to ZIP for 3 h. ZIP and its metabolites can exert cytotoxic activities due to significant decreases in mitotic index, proliferation index and nuclear division index in the presence and absence of S9 mix. Statistically significant increases in CAs, aberrant cells and MN values in the presence and absence of S9 mix were found in cultures treated with ZIP. While ZIP significantly increased the SCE values in the absence of S9 mix at all concentrations, increased SCE values in cultures with S9 mix were not found to significantly at all concentrations tested. Our results indicated that both ZIP and its metabolites have cytotoxic, cytostatic and genotoxic potential on lymphocyte cultures under the experimental conditions. Further studies are necessary to make a possible risk assessment in patients receiving therapy with this drug.

In vitro potential cytogenetic and oxidative stress effects of roxithromycin.

Macrolide antibiotic roxithromycin was evaluated in terms of its genotoxic, cytotoxic and oxidative stress effects. For this purpose; 25, 50, 100 and 200 µg/mL concentrations of roxithromycin were dissolved in dimethyl sulfoxide and treated to human peripheral blood lymphocytes for two different treatment periods (24 and 48 h). In chromosome aberration (CA) and micronucleus (MN) tests, roxithromycin did not show genotoxic effect. But it induced sister chromatid exchange (SCE) at the highest concentration (200 µg/mL) for the 24-h treatment period and at all concentrations (except 25 µg/mL) for the 48-h treatment period. Looking at cytotoxic effect of roxithromycin, statistically insignificant decreases on mitotic index and proliferation index were observed. Roxithromycin decreased nuclear division index (NDI) at highest two concentrations (100 and 200 µg/mL) for the 24-h treatment period and at all concentrations (expect 25 µg/mL) for the 48-h treatment period. Total oxidant values, total antioxidant values and oxidative stress index did not change with roxithromycin treatment. Eventually, roxithromycin did not have genotoxic and oxidative stress effects in human-cultured lymphocytes.

Determination of mutagenicity and genotoxicity of indium tin oxide nanoparticles using the Ames test and micronucleus assay.

In this study, the mutagenicity and genotoxicity of indium tin oxide (ITO) nanomaterial were assessed using two standard genotoxicity assays, the Salmonella reverse mutation assay (Ames test) and the in vitro micronucleus (MN) assay. Seven different concentrations (12.5, 25, 50, 75, 100, 125, and 150 µg/plate) of this nanomaterial were tested using the Ames test on the TA98 and TA100 strains in the presence and absence of the S9 mixture. At all the concentrations tested, this substance did not significantly increase the number of revertant colonies compared with the control with or without S9 mixture. The genotoxic effects of ITO were investigated in human peripheral lymphocytes treated with 125, 250, 500, and 750 µg/ml concentrations of this substance for 24- and 48-h treatment periods using an MN test. Nuclear division index (NDI) was also calculated in order to determine the cytotoxicity of ITO. It was determined that ITO increased MN frequency in the 750 µg/ml concentration in 24- and 48-h treatments. In addition, ITO dose dependently decreased the NDI significantly for two treatment periods.

Aberrant cytokinesis and cell fusion result in multinucleation in HepG2 cells exposed to silica nanoparticles.

The multinucleation effect of silica nanoparticles (SiNPs) had been determined in our previous studies, but the relative mechanisms of multinucleation and how the multinucleated cells are generated were still not clear. This extensional study was conducted to investigate the mechanisms underlying the formation of multinucleated cells after SiNPs exposure. We first investigated cellular multinucleation, then performed time-lapse confocal imaging to certify whether the multinucleated cells resulted from cell fusion or abnormal cell division. Our results confirmed for the first time that there are three patterns contributing to the SiNPs-induced multinucleation in HepG2 cells: cell fusion, karyokinesis without cytokinesis, and cytokinesis followed by fusion. The chromosomal passenger complex (CPC) deficiency and cell cycle arrest in G1/S and G2/M checkpoints may be responsible for the cell aberrant cytokinesis. The activated MAPK/ERK1/2 signaling and decreased mitosis related proteins might be the underlying mechanism of cell cycle arrest and thus multinucleation. In summary, we confirmed the hypothesis that aberrant cytokinesis and cell fusion resulted in multinucleation in HepG2 cells after SiNPs exposure. Since cell fusion and multinucleation were involved in genetic instability and tumor development, this study suggests the potential ability of SiNPs to induce cellular genetic instability. These findings raise concerns with regard to human health hazards and environmental risks with SiNPs exposure.

Development of ichthyosporeans sheds light on the origin of metazoan multicellularity.

To understand the mechanisms involved in the transition from protists to multicellular animals (metazoans), studying unicellular relatives of metazoans is as important as studying metazoans themselves. However, investigations remain poor on the closest unicellular (or colonial) relatives of Metazoa, i.e., choanoflagellates, filastereans and ichthyosporeans. Molecular-level analyses on these protists have been severely limited by the lack of transgenesis tools. Their genomes, however, contain several key genes encoding proteins important for metazoan development and multicellularity, including those involved in cell-cell communication, cell proliferation, cell differentiation, and tissue growth control. Tools to analyze their functions in a molecular level are awaited. Here we report techniques of cell transformation and gene silencing developed for the first time in a close relative of metazoans, the ichthyosporean Creolimax fragrantissima. We propose C. fragrantissima as a model organism to investigate the origin of metazoan multicellularity. By transgenesis, we demonstrate that its colony develops from a fully-grown multinucleate syncytium, in which nuclear divisions are strictly synchronized. It has been hypothesized that metazoan multicellular development initially occurred in the course of evolution through successive rounds of cell division, which were not necessarily be synchronized, or alternatively through cell aggregation. Our findings point to another possible mechanism for the evolution of animal multicellularity, namely, cellularization of a syncytium in which nuclear divisions are synchronized. We believe that further studies on the development of ichthyosporeans by the use of our methodologies will provide novel insights into the origin of metazoan multicellularity.

Arrest of nuclear division in Plasmodium through blockage of erythrocyte surface exposed ribosomal protein P2.

Malaria parasites reside inside erythrocytes and the disease manifestations are linked to the growth inside infected erythrocytes (IE). The growth of the parasite is mostly confined to the trophozoite stage during which nuclear division occurs followed by the formation of cell bodies (schizogony). The mechanism and regulation of schizogony are poorly understood. Here we show a novel role for a Plasmodium falciparum 60S stalk ribosomal acidic protein P2 (PfP2) (PFC0400w), which gets exported to the IE surface for 6-8 hrs during early schizogony, starting around 26-28 hrs post-merozoite invasion. The surface exposure is demonstrated using multiple PfP2-specific monoclonal antibodies, and is confirmed through transfection using PfP2-GFP. The IE surface-exposed PfP2-protein occurs mainly as SDS-resistant P2-homo-tetramers. Treatment with anti-PfP2 monoclonals causes arrest of IEs at the first nuclear division. Upon removal of the antibodies, about 80-85% of synchronized parasites can be released even after 24 hrs of antibody treatment. It has been reported that a tubovesicular network (TVN) is set up in early trophozoites which is used for nutrient import. Anti-P2 monoclonal antibodies cause a complete fragmentation of TVN by 36 hrs, and impairs lipid import in IEs. These may be downstream causes for the cell-cycle arrest. Upon antibody removal, the TVN is reconstituted, and the cell division progresses. Each of the above properties is observed in the rodent malaria parasite species P. yoelii and P. berghei. The translocation of the P2 protein to the IE surface is therefore likely to be of fundamental importance in Plasmodium cell division.

ApoA-II directs morphogenetic movements of zebrafish embryo by preventing chromosome fusion during nuclear division in yolk syncytial layer.

The high density lipoprotein (HDL) represents a class of lipid- and protein-containing particles and consists of two major apolipoproteins apoA-I and apoA-II. ApoA-II has been shown to be involved in the pathogenesis of insulin resistance, adiposity, diabetes, and metabolic syndrome. In embryo, apoa2 mRNAs are abundant in the liver, brain, lung, placenta, and in fish yolk syncytial layer (YSL), suggesting that apoa2 may perform a function during embryonic development. Here we find out that apoa2 modulates zebrafish embryonic development by regulating the organization of YSL. Disruption of apoa2 function in zebrafish caused chromosome fusing, which strongly blocked YSL nuclear division, inducing disorders in YSL organization and finally disturbing the embryonic epiboly. Purified native human apoA-II was able specifically to rescue the defects and induced nuclear division in zebrafish embryos and in human HeLa cells. The C terminus of apoA-II was required for the proper chromosome separation during nuclear division of YSL in zebrafish embryos and in human HeLa cells. Our data indicate that organization of YSL is required for blastoderm patterning and morphogenesis and suggest that apolipoprotein apoA-II is a novel factor of nuclear division in YSL involved in the regulation of early zebrafish embryonic morphogenesis and in mammalian cells for proliferation.

Differences in apoptotic status in the bovine placentome between spontaneous and induced parturition.

We conducted this study to analyze apoptotic changes in the bovine placentome at spontaneous and induced parturition. Cows delivered i) after the administration of dexamethasone followed by prostaglandin F(2α) and estriol, ii) after the administration of prostaglandin F(2α) and estriol or iii) spontaneously. Prepartum changes in plasma progesterone and estradiol-17ß concentrations were similar between spontaneous and induced parturition. Messenger RNA of BCL2-related protein A1 (BCL2A1), an antiapoptotic gene, was expressed by trophoblast binucleate cells and caruncular epithelial cells. Quantitative RT-PCR showed that the expression of BCL2A1 mRNA in cotyledonary and caruncular portions was significantly lower in spontaneous parturition than induced parturition. The expression of BCL2-associated X protein (BAX) mRNA, a proapoptotic gene, was significantly higher in cotyledons at spontaneous parturition than parturition induced without dexamethasone. Caspase-3 (CASP3) mRNA and pre-activated CASP3 protein were predominantly detected in caruncular epithelial cells regardless of how parturition proceeded. Activated CASP3 protein was found in trophoblast uninucleate cells and binucleate cells rather than caruncular epithelial cells. In spontaneous parturition, intense staining of activated CASP3 was detected in caruncular epithelial cells. Spontaneous and dexamethasone-induced parturition increased apoptotic cells in the placentome compared with parturition induced without dexamethasone. The number of binucleate cells was significantly decreased in spontaneous parturition. The present results suggest that although the clinical dose of dexamethasone induces apoptosis in the placentome at term, neither dexamethasone nor prostaglandin F(2α) evoke normal physiological changes in the placentome during delivery such as a change in the balance of apoptosis-related genes and disappearance of binucleate cells.

The evaluation of the genotoxic and oxidative damage potentials of Ulothrix tenuissima (Kutz.) in vitro.

Several alga species are known to produce a variety of toxic metabolites that pose a threat to aquatic organisms, animals and humans. Moreover, these metabolites have been thought to cause serious diseases including certain cancers and neurodegenerative disorders. On the other hand, Ulothrix is a genus of filamentous green algae, generally found in fresh water and marine and abundantly available in some lakes and rivers of Turkey. To our best knowledge, no study has been performed to assess the genotoxic and biochemical effects of U. tenuissima on cultured human blood cells. Therefore, in order to determine clastogenic or aneugenic effects of aqueous alga extracts the micronucleus assay was carried out. Nuclear division index (NDI) in peripheral lymphocytes was also analyzed for cytotoxicity evaluations. In addition, biochemical parameters (total antioxidant capacity (TAC) and total oxidative stress (TOS)) were examined to determine oxidative effects. For this aim, we obtained heparinized blood samples from three healthy persons. The alga samples were collected from Porsuk Pond in Hasankale (Erzurum, Turkey) in summer period of the year 2010. The aqueous extracts of this species were added to cultures at different concentrations (0 to 5000 ppm) for 72 h. Our results showed that this alga did not cause any statistically important changes in the rates of studied genotoxicity endpoint. But dose-dependent alterations were observed in TAC and TOS levels and NDI rates. In conclusion, U. tenuissima was found to be non-genotoxic but caused sterility at higher concentrations due to oxidative stress.

Cdc25B cooperates with Cdc25A to induce mitosis but has a unique role in activating cyclin B1-Cdk1 at the centrosome.

Cdc25 phosphatases are essential for the activation of mitotic cyclin-Cdks, but the precise roles of the three mammalian isoforms (A, B, and C) are unclear. Using RNA interference to reduce the expression of each Cdc25 isoform in HeLa and HEK293 cells, we observed that Cdc25A and -B are both needed for mitotic entry, whereas Cdc25C alone cannot induce mitosis. We found that the G2 delay caused by small interfering RNA to Cdc25A or -B was accompanied by reduced activities of both cyclin B1-Cdk1 and cyclin A-Cdk2 complexes and a delayed accumulation of cyclin B1 protein. Further, three-dimensional time-lapse microscopy and quantification of Cdk1 phosphorylation versus cyclin B1 levels in individual cells revealed that Cdc25A and -B exert specific functions in the initiation of mitosis: Cdc25A may play a role in chromatin condensation, whereas Cdc25B specifically activates cyclin B1-Cdk1 on centrosomes.

Developmental competence of oocytes recovered from postmortem ovaries of the endangered Indian blackbuck (Antilope cervicapra).

The ability to rescue gametes from endangered or wildlife species and to subsequently produce viable embryos holds tremendous potential as a means to increase the population size of endangered or wildlife species. The objective of this study was to assess the meiotic and developmental competence of oocytes recovered from postmortem ovaries of the Indian blackbuck. Oocytes collected from the ovaries of dead blackbucks were allowed to mature in vitro and then tested for developmental potential by activation with ionomycin followed by treatment with 6-dimethylaminopurine. The average number of oocytes recovered per ovary was 10.9, and recovery of the oocytes did not depend on the presence or absence of the corpus luteum, on the side, size and weight of the ovaries or on the type of oocytes recovered. The proportion of good quality oocytes showing cumulus expansion and extrusion of the first polar body were 79.3% and 46.1% when cultured with gonadotropins. In vitro maturation studies indicated that the proportion of oocytes that reached MII stage was significantly higher when good quality oocytes (68%) were used compared with fair quality oocytes (48%) when cultured in the presence of gonadotropins. Furthermore, fifty eight percent of the in vitro matured oocytes cleaved, and thirteen percent of the cleaved oocytes developed into blastocysts. These findings suggest that the oocytes recovered from postmortem ovaries of the blackbuck can be utilized for production of embryos.

Methylglyoxal inhibits nuclear division through alterations in vacuolar morphology and accumulation of Atg18 on the vacuolar membrane in Saccharomyces cerevisiae.

Methylglyoxal (MG) is a natural metabolite derived from glycolysis, and it inhibits the growth of cells in all kinds of organisms. We recently reported that MG inhibits nuclear division in Saccharomyces cerevisiae. However, the mechanism by which MG blocks nuclear division remains unclear. Here, we show that increase in the levels of phosphatidylinositol 3,5-bisphosphate (PtdIns(3,5)P2) is crucial for the inhibitory effects of MG on nuclear division, and the deletion of PtdIns(3,5)P2-effector Atg18 alleviated the MG-mediated inhibitory effects. Previously, we reported that MG altered morphology of the vacuole to a single swelling form, where PtdIns(3,5)P2 accumulates. The changes in the vacuolar morphology were also needed by MG to exert its inhibitory effects on nuclear division. The known checkpoint machinery, including the spindle assembly checkpoint and morphological checkpoint, are not involved in the blockade of nuclear division by MG. Our results suggest that both the accumulation of Atg18 on the vacuolar membrane and alterations in vacuolar morphology are necessary for the MG-induced inhibition of nuclear division.

Visualization of aberrant perinuclear microtubule aster organization by microtubule-destabilizing agents.

To analyze aberrant spindle formation by microtubule-targeting drugs, live cell imaging was performed using multi-fluorescent human MDA-MB-435 cells in which several spindle components were visualized. Time-lapse images revealed that nocodazole and vinblastine induced additional perinuclear asters at the onset of mitosis. These results imply that these drugs stimulate the microtubule-organizing activity, despite their microtubule-destabilizing properties.

Fluorodeoxyuridine mediated cell cycle synchronization in S-phase increases the Auger radiation cell killing with 125I-iododeoxyuridine.

AIM: 125I-iododeoxyuridine is a potential Auger radiation therapy agent. Its incorporation in DNA of proliferating cells is enhanced by fluorodeoxyuridine. Here, we evaluated therapeutic activities of 125I-iododeoxyuridine in an optimized fluorodeoxyuridine pre-treatment inducing S-phase synchronization. METHODS: After S-phase synchronization by fluorodeoxyuridine, cells were treated with 125I-iododeoxyuridine. Apoptosis analysis and S-phase synchronization were studied by flow cytometry. Cell survival was determined by colony-forming assay. Based on measured growth parameters, the number of decays per cell that induced killing was extrapolated. RESULTS: Treatment experiments showed that 72 to 91% of synchronized cells were killed after 0.8 and 8 kBq/ml 125I-iododeoxyuridine incubation, respectively. In controls, only 8 to 38% of cells were killed by corresponding 125I-iododeoxyuridine activities alone and even increasing the activity to 80 kBq/ml gave only 42 % killing. Duplicated treatment cycles or repeated fluorodeoxyuridine pre-treatment allowed enhancing cell killing to >95 % at 8 kBq/ml 125I-iododeoxyuridine. About 50 and 160 decays per S-phase cells in controls and S-phase synchronization, respectively, were responsible for the observed cell killing at 0.8 kBq/ml radio-iododeoxyuridine. CONCLUSION: These data show the successful application of fluorodeoxyuridine that provided increased 125I-iododeoxyuridine Auger radiation cell killing efficacy through S-phase synchronization and high DNA incorporation of radio-iododeoxyuridine.

Identification of Saccharomyces cerevisiae Tub1 alpha-tubulin as a potential target for NKH-7, a cytotoxic 1-naphthol derivative compound.

In a screening for small-molecule compounds that alleviate the deleterious effects of external CaCl(2) on zds1 Delta strain yeast, we found 2-((1-(hydroxymethyl) cyclohexyl) methyl) naphthalen-1-ol (NKH-7) to be an active compound. NKH-7 also inhibited cell growth at higher concentrations. To identify its target in growth inhibition, we isolated NKH-7-resistant mutants and selected those mutants that exhibited dominant or semi-dominant resistance specifically to NKH-7. By gene cloning, a TUB1 mutant gene encoding alpha-tubulin with a Ser248Pro mutation was identified. Deletion of the TUB3 gene, a minor gene encoding alpha-tubulin, led to supersensitivity to NKH-7. Cellular tubulin-containing arrays as visualized by green fluorescent protein (GFP)-labeled alpha-tubulin diminished rapidly on exposure to the inhibitor. The mutation was situated proximal to the alpha-beta interface of alpha-tubulin in microtubule protofilaments, suggesting the possibility that NKH-7 affects the hydrolysis of GTP bound to beta-tubulin. A functional connection perhaps exists between the tubulin inhibition and Ca(2+)-dependent cell-cycle regulation.

TPA-induced multinucleation of a mesenchymal stem cell-like clone is mediated primarily by karyokinesis without cytokinesis, although cell-cell fusion also occurs.

The 5F9A cell, which is a mesenchymal stem cell-like clone established from rat bone marrow substrate adherent cells, can differentiate into adipocytes and osteoblasts in vitro under the appropriate conditions. Multinucleated cells could be also induced by 12-O-tetradecanoylphorbol 13-acetate (TPA) in 5F9A cells. This effect was mediated by protein kinase C. Possible mechanisms of multinucleation by TPA were hypothesized to be either karyokinesis without cytokinesis or cell-cell fusion. By observation using time-lapse phase-contrast microscopy, we determined that the multinucleated cells were generated mainly by karyokinesis without cytokinesis. Cell fusion was studied using time-lapse photography, and confocal laser scanning microscopy using two differentially labeled cells. These techniques demonstrated that multinucleated 5F9A cells could be produced by cell fusion, albeit at a low frequency. We conclude that multinucleated 5F9A cells are formed primarily by karyokinesis without cytokinesis, although some cells are also formed by cell-cell fusion.

Flow cytometric cell cycle analysis allows for rapid screening of estrogenicity in MCF-7 breast cancer cells.

The quantitative measurement of individual cells and their characteristics by means of flow cytometry is already for many years of great value for clinical studies. However, its potential as a tool in (eco)toxicology has only recently been discovered. Analysis of cell cycle kinetics with DNA-staining dyes can offer a valuable alternative to detect effects of chemicals on cell proliferation, an important endpoint in screening estrogen-like properties of chemicals. In the present study, flow cytometric cell cycle analysis in growth arrested MCF-7 cells exposed to five xenoestrogens correspond well with cell proliferation results of the conventionally used E-screen assay. Moreover, re-induction of proliferation in MCF-7 cells, indicated by the percentage of cells in S(ynthesis)-phase, is most pronounced after 24 h exposure, thus allowing a faster screening of xenoestrogens. This flow cytometric proliferation assay confirms that the estrogenic activity of structurally analogous parabens is mediated by the estrogen receptor pathway and is proportional to the alkyl chain length. Moreover, the ER-mediated mode of action of two fluorotelomer alcohols (6:2 FTOH and 8:2 FTOH), recently reported as xenoestrogenic, could be elucidated. These results support the potential of flow cytometric cell cycle kinetics as a screening assay for estrogen-like properties of chemicals.