Pole position: How plant cells polarize along the axes

Having a sense of direction is a fundamental cellular trait that can determine cell shape, division orientation, or function, and ultimately the formation of a functional, multicellular body. Cells acquire and integrate directional information by establishing discrete subcellular domains along an axis with distinct molecular profiles, a process known as cell polarization. Insight into the principles and mechanisms underlying cell polarity has been propelled by decades of extensive research mostly in yeast and animal models. Our understanding of cell polarity establishment in plants, which lack most of the regulatory molecules identified in other eukaryotes, is more limited, but significant progress has been made in recent years. In this review, we explore how plant cells coordinately establish stable polarity axes aligned with the organ axes, highlighting similarities in the molecular logic used to polarize both plant and animal cells. We propose a classification system for plant cell polarity events and nomenclature guidelines. Finally, we provide a deep phylogenetic analysis of polar proteins and discuss the evolution of polarity machineries in plants.

This review discusses the principles, mechanisms, and evolution of plant cell polarity, an essential cellular feature for plant development and physiology that endows cells with a sense of direction.     

In vivo micronucleus assays on 2,4-dichlorophenoxyacetic acid and its derivatives.

The potential for 2,4-D and seven of its salts and esters to induce cytogenetic abnormalities in mammalian cells in vivo was investigated in the mouse bone marrow micronucleus test. All the test materials were administered to male and female mice by oral gavage and the frequencies of micronucleated polychromatic erythrocytes (MN-PCE) in the bone marrow were determined at intervals of 24, 48 and 72 h following dosing. There were no significant increases in the incidence of MN-PCE in the treated mice at any of the bone marrow sampling times. These results are consistent with the reported lack of in vitro genetic toxicity for these materials in various in vitro genotoxicity assays as well as the absence of carcinogenic potential for 2,4-D in both mice and rats.     

Role of NF-kappaB signaling pathway in increased tumor necrosis factor-alpha-induced apoptosis of lymphocytes in aged humans

In human aging, lymphocytes display increased sensitivity to tumor necrosis factor-alpha (TNF-alpha)-induced apoptosis. TNF-alpha induces both survival and apoptotic signals. The survival signal is mediated by the activation of NF-kappaB. Although a role of certain proapoptotic molecules in aging has been reported, a role of altered NF-kappaB signaling pathway has not been explored in detail. In this study, we have compared TNF-alpha-induced activation of NF-kappaB, phosphorylation of IkappaBalpha, and the expression of IKKbeta between lymphocytes from young and aged humans. Furthermore, we have explored a role of IKKbeta in increased susceptibility of lymphocytes from aged humans to TNF-alpha-induced apoptosis. Lymphocytes from aged humans displayed decreased activation of NF-kappaB, reduced phosphorylation of IkappaBalpha, and decreased expression of IKKbeta. In addition, overexpression of IKKbeta in lymphocytes from aged humans normalized TNF-alpha-induced apoptosis to the level of young subjects. These data suggest a deficiency of NF-kappaB signaling pathway and a role of IKKbeta, at least in part, for increased sensitivity of lymphocytes from aged humans to TNF-alpha-induced apoptosis.     

Mouse lymphoma thymidine kinase gene mutation assay: meeting of the International Workshop on Genotoxicity Testing, San Francisco, 2005, recommendations for 24-h treatment

The Mouse Lymphoma Assay (MLA) Workgroup of the International Workshop on Genotoxicity Testing (IWGT), comprised of experts from Japan, Europe and the United States, met on September 9, 2005, in San Francisco, CA, USA. This meeting of the MLA Workgroup was devoted to reaching a consensus on issues involved with 24-h treatment. Recommendations were made concerning the acceptable values for the negative/solvent control (mutant frequency, cloning efficiency and suspension growth) and the criteria to define an acceptable positive control response. Consensus was also reached concerning the use of the global evaluation factor (GEF) and appropriate statistical trend analysis to define positive and negative responses for the 24-h treatment. The Workgroup agreed to continue their support of the International Committee on Harmonization (ICH) recommendation that the MLA assay should include a 24-h treatment (without S-9) in those situations where the short treatment (3-4 h) gives negative results.     

Mouse Lymphoma Thymidine Kinase Gene Mutation Assay: International Workshop on Genotoxicity Tests Workgroup Report—Plymouth, UK 2002

The Mouse Lymphoma Assay (MLA) Workgroup of the International Workshop on Genotoxicity Tests (IWGT) met on June 28th and 29th, 2002, in Plymouth, England. This meeting of the MLA group was devoted to discussing the criteria for assay acceptance and appropriate approaches to data evaluation. Prior to the meeting, the group conducted an extensive analysis of data from both the microwell and soft agar versions of the assay. For the establishment of criteria for assay acceptance, 10 laboratories (6 using the microwell method and 4 using soft agar) provided data on their background mutant frequencies, plating efficiencies of the negative/vehicle control, cell suspension growth, and positive control mutant frequencies. Using the distribution curves generated from this data, the Workgroup reached consensus on the range of values that should be used to determine whether an individual experiment is acceptable. In order to establish appropriate approaches for data evaluation, the group used a number of statistical methods to evaluate approximately 400 experimental data sets from 10 laboratories entered into a database created for the earlier MLA Workshop held in New Orleans [Environ. Mol. Mutagen. 40 (2002) 292]. While the Workgroup could not, during this meeting, make a final recommendation for the evaluation of data, a general strategy was developed and the Workgroup members agreed to evaluate this new proposed approach using their own laboratory data. This evaluation should lead to a consensus global approach for data evaluation in the near future.     

Analyses for in vitro growth conditions,cytokinetics, and sister chromatid exchanges in lymphocytes cultured from the Sprague-Dawley rat

Summary Peripheral blood samples from Sprague-Dawley rats gave successful lymphocyte growth in GIBCO: IA, RPMI 1640, and Eagle's minimum essential medium (MEM) culture media. Various growth conditions, cytokinetics, and sister chromatic exchange (SCE) induction were studied using reconstituted GIBCO 1A only. Neither methoxyflurane anesthesia of the rats before sampling nor washing of the cells with phosphate buffered saline affected the mitotic index. Cultures treated with [³H]thymidine showed the lymphocytes entering into DNA synthesis after approximately 24 h. The time at which BUdR (5-bromo-2′ deoxyuridine) was added, i.e. 0 vs. 24 h incubation, had minimal effect on the mitotic index of cultures harvested at 48 h. However, when harvest was extended to 72 h, mitotic activity was greater in the cultures treated with BUdR at 24 h. No significant differences in mitotic index and the number of average lymphocyte division were detected in cultures exposed to 0.3 to 0.5 μg/ml BUdR at 24 h and harvested at 72 h. Although SCE frequencies increased in the presence of BUdR, the baseline level of SCEs was estimated to be 5 to 6/cell. Average generation time of the lymphocytes dividing between 48 and 72 h was 16.5 h. Because of its simplicity of culture and the reproducible nature of its in vitro growth kinetics, the Sprague-Dawley rat lymphocyte is a suitable model for cytogenetic investigations.     

Genetic toxicity and carcinogenicity studies of glutaraldehyde--a review

Glutaraldehyde is a high production volume chemical that is highly reactive and has many medical and industrial uses. The majority of human exposures are via inhalation, but the exposure is not widespread. It has been extensively tested for genetic activity in vitro and in vivo, and there is disagreement in the literature with regard to glutaraldehyde's genetic activity. Glutaraldehyde produced DNA damage in bacteria and some cultured mammalian cell systems. In vitro, it was mutagenic in Salmonella and E. coli, produced inconsistent positive responses in mammalian cells, weak and inconsistent responses in chromosome aberration and SCE studies, and did not induce transformation in cultured SHE cells. In vivo, inhalation of glutaraldehyde induced cell proliferation in nasal tissue in rats and mice, but DNA damage and UDS were not induced at these sites in rats. Chromosome aberrations in bone marrow cells were reported in only one of eight studies using rats and mice, micronuclei were not induced in bone marrow cells of mice, and dominant lethal mutations were not induced in mice. Glutaraldehyde did not induce cell transformation in SHE cells in vitro. Bone marrow hyperplasia and low, but statistically significant, levels of leukemia were seen in one chronic drinking water study in rats, but not in a chronic inhalation study in rats or two chronic inhalation studies in mice.