The tarani mutation alters surface curvature in Arabidopsis leaves by perturbing the patterns of surface expansion and cell division

The leaf surface usually stays flat, maintained by coordinated growth. Growth perturbation can introduce overall surface curvature, which can be negative, giving a saddle-shaped leaf, or positive, giving a cup-like leaf. Little is known about the molecular mechanisms that underlie leaf flatness, primarily because only a few mutants with altered surface curvature have been isolated and studied. Characterization of mutants of the CINCINNATA-like TCP genes in Antirrhinum and Arabidopsis have revealed that their products help maintain flatness by balancing the pattern of cell proliferation and surface expansion between the margin and the central zone during leaf morphogenesis. On the other hand, deletion of two homologous PEAPOD genes causes cup-shaped leaves in Arabidopsis due to excess division of dispersed meristemoid cells. Here, we report the isolation and characterization of an Arabidopsis mutant, tarani (tni), with enlarged, cup-shaped leaves. Morphometric analyses showed that the positive curvature of the tni leaf is linked to excess growth at the centre compared to the margin. By monitoring the dynamic pattern of CYCLIN D3;2 expression, we show that the shape of the primary arrest front is strongly convex in growing tni leaves, leading to excess mitotic expansion synchronized with excess cell proliferation at the centre. Reduction of cell proliferation and of endogenous gibberellic acid levels rescued the tni phenotype. Genetic interactions demonstrated that TNI maintains leaf flatness independent of TCPs and PEAPODs.

Stability Of Adhesion Clusters And Cell Reorientation Under Lateral Cyclic Tension

This work is motivated by experimental observations that cells on stretched substrate exhibit different responses to static and dynamic loads. A model of focal adhesion that can consider the mechanics of stress fiber, adhesion bonds, and substrate was developed at the molecular level by treating the focal adhesion as an adhesion cluster. The stability of the cluster under dynamic load was studied by applying cyclic external strain on the substrate. We show that a threshold value of external strain amplitude exists beyond which the adhesion cluster disrupts quickly. In addition, our results show that the adhesion cluster is prone to losing stability under high-frequency loading, because the receptors and ligands cannot get enough contact time to form bonds due to the high-speed deformation of the substrate. At the same time, the viscoelastic stress fiber becomes rigid at high frequency, which leads to significant deformation of the bonds. Furthermore, we find that the stiffness and relaxation time of stress fibers play important roles in the stability of the adhesion cluster. The essence of this work is to connect the dynamics of the adhesion bonds (molecular level) with the cell's behavior during reorientation (cell level) through the mechanics of stress fiber. The predictions of the cluster model are consistent with experimental observations.

Lymphangioleiomyomatosis Biomarkers Linked to Lung Metastatic Potential and Cell Stemness

Lymphangioleiomyomatosis (LAM) is a rare lung-metastasizing neoplasm caused by the proliferation of smooth muscle-like cells that commonly carry loss-of-function mutations in either the tuberous sclerosis complex 1 or 2 (TSC1 or TSC2) genes. While allosteric inhibition of the mechanistic target of rapamycin (mTOR) has shown substantial clinical benefit, complementary therapies are required to improve response and/or to treat specific patients. However, there is a lack of LAM biomarkers that could potentially be used to monitor the disease and to develop other targeted therapies. We hypothesized that the mediators of cancer metastasis to lung, particularly in breast cancer, also play a relevant role in LAM. Analyses across independent breast cancer datasets revealed associations between low TSC1/2 expression, altered mTOR complex 1 (mTORC1) pathway signaling, and metastasis to lung. Subsequently, immunohistochemical analyses of 23 LAM lesions revealed positivity in all cases for the lung metastasis mediators fascin 1 (FSCN1) and inhibitor of DNA binding 1 (ID1). Moreover, assessment of breast cancer stem or luminal progenitor cell biomarkers showed positivity in most LAM tissue for the aldehyde dehydrogenase 1 (ALDH1), integrin-beta 3 (ITGB3/CD61), and/or the sex-determining region Y-box 9 (SOX9) proteins. The immunohistochemical analyses also provided evidence of heterogeneity between and within LAM cases. The analysis of Tsc2-deficient cells revealed relative over-expression of FSCN1 and ID1; however, Tsc2-deficient cells did not show higher sensitivity to ID1-based cancer inhibitors. Collectively, the results of this study reveal novel LAM biomarkers linked to breast cancer metastasis to lung and to cell stemness, which in turn might guide the assessment of additional or complementary therapeutic opportunities for LAM.

Microcystin-RR induces physiological stress and cell death in the cyanobacterium Aphanizomenon sp DC01 isolated from Lake Dianchi, China

The phytoplankton community in Lake Dianchi (Yunnan Province, Southwestern China) is dominated in April by a bloom of Aphanizomenon, that disappears Suddenly and is displaced by a Microcystis bloom in May. The reasons for the rapid bloom disappearance phenomenon and the temporal variability in the composition of phytoplankton assemblages are poorly understood. Cell growth, ultrastructure and physiological changes were examined in cultures of Aphanizomenon sp. DC01 isolated from Lake Dianchi exposed to different closes of rnicrocystin-RR (MC-RR) produced by the Microcystis bloom. MC-RR concentrations above 100 mu g L-1 markedly inhibited the pigment (chlorophyll-a, phycocyanin) synthesis and caused an increase of soluble carbohydrate and protein contents and nitrate reductase activity of toxin-treated blue-green algae. A drastic. reduction in photochemical efficiency of PSII (Fv/Fm) was also found. Morphological examinationn showed that the Aphanizomenon filaments disintegrated and file cells lysed gradually after 48 h Of toxin exposure. Transmission electron microscopy revealed that cellular inclusions of stressed cells almost leaked out completely and the cell membranes were grossly damaged. These findings demonstrate the allelopathic activity of Microcystis aeruginosa inducing physiological stress and cell death of Aphanizomenon sp. DC01 Although the active concentrations of microcystin were rather high, we propose that microcystin may function as allelopathic Substance due to inhomogeneous toxin concentrations close to Microcystis cells. Hence, it may play a role in species Succession of Aphanizomenon and Microcystis in Lake Dianchi.

Cellular contractility and substrate elasticity: A numerical investigation of the actin cytoskeleton and cell adhesion

Numerous experimental studies have established that cells can sense the stiffness of underlying substrates and have quantified the effect of substrate stiffness on stress fibre formation, focal adhesion area, cell traction, and cell shape. In order to capture such behaviour, the current study couples a mixed mode thermodynamic and mechanical framework that predicts focal adhesion formation and growth with a material model that predicts stress fibre formation, contractility, and dissociation in a fully 3D implementation. Simulations reveal that SF contractility plays a critical role in the substrate-dependent response of cells. Compliant substrates do not provide sufficient tension for stress fibre persistence, causing dissociation of stress fibres and lower focal adhesion formation. In contrast, cells on stiffer substrates are predicted to contain large amounts of dominant stress fibres. Different levels of cellular contractility representative of different cell phenotypes are found to alter the range of substrate stiffness that cause the most significant changes in stress fibre and focal adhesion formation. Furthermore, stress fibre and focal adhesion formation evolve as a cell spreads on a substrate and leading to the formation of bands of fibres leading from the cell periphery over the nucleus. Inhibiting the formation of FAs during cell spreading is found to limit stress fibre formation. The predictions of this mutually dependent material-interface framework are strongly supported by experimental observations of cells adhered to elastic substrates and offer insight into the inter-dependent biomechanical processes regulating stress fibre and focal adhesion formation. © 2013 Springer-Verlag Berlin Heidelberg.

Regulation by hetC of genes required for heterocyst differentiation and cell division in Anabaena sp strain PCC 7120

Unlike those of the wild-type strain, proheterocysts of the Anabaena sp. strain PCC 7120 hetC strain keep dividing. ftsZ, the most critical cell division gene, is up-regulated in hetC proheterocysts. Heterocyst differentiation genes hglD, hglE, patB, nijB, and xisA are no longer expressed in the hetC mutant. hetC also regulates the expression of patA, a pattern formation gene.

Changes in culture growth dynamics and cell size in a Scenedesmus quadricauda upon action of potassium dichromate

The effect of potassium dichromate in concentrations of 0.5 to 10 mg/l on a laboratory culture of Sc. quadricauda algae was studied in standard conditions. The total cell numbers decreased at potassium dichromate concentrations over 1 mg/l, and the proportion of living cells decreased at all studied concentrations. A positive correlation was found between changes in cell size and their numbers at toxin concentrations of 1 and 3 mg/l, and a negative correlation was found between the relative size and the cell numbers at 3 and 10 mg/l. This may be due to different intensity of growth inhibition and cell division under the influence of the toxin. The culture sensitivity to the toxin increased in autumn and decreased in the spring.

Effect of 80.55 MeV/u(12)C(6+) ions on radiosensitivity and cell cycle of human hepatoma cell lines

In this paper, the relationship between radiosensitivity, cell cycle alteration and the change of apoptosis in different human hepatoma cell lines irradiated by heavy ions were studied with the aim of building up the base data for clinical therapy. Exponentially growing hepatoma cell lines were irradiated by 80.55 MeV/u(12)C(6+) ions at a dose of 0 Gy, 0.5 Gy, 1 Gy, 2 Gy, 4 Gy and 8 Gy. The radiosensitivity was assessed by means of the colony-forming assay. The DNA content, the percentage of each cell-cycle phase and the apoptosis rate were obtained with flow cytometry methods. After the irradiation, the SF2 (survival fraction at 2 gray) of SMMC-7721 cells were evidently lower than that of HepG2 cells. The S phase arrest, G2/M phase arrest delay and the apoptosis in the two hepatoma cell lines varied with the increase of the dose and repair time. The heavy ions could obviously kill the human hepatoma cell lines. Compared to HepG2 cells, SMMC-7721 cells were more radiosensitive to C-12(6+) ions.

Effects of hydrostatic pressure on microtubule organization and cell cycle in gynogenetically activated eggs of olive flounder (Paralichthys olivaceus)

Indirect immunofluorescence staining was used to detect cytological changes of isolated blastodisks during mitosis of flounder haploid eggs treated with hydrostatic pressure. Changes in microtubule structure and expected cleavage suppression were observed from blastodisk formation to the third cell cycle, with obvious differences between treated and control eggs. In most eggs, microtubules were disassembled and the nucleation capacity of the centrosome was temporarily inhibited after pressure treatment. Within 15-20 min after treatment, the nucleation capacity of the centrosome began to gradually recover, with slow regeneration of microtubules; approximately 25 min after treatment, the nucleation capacity of the centrosome recovered completely, regenerated distinct bipolar spindles, and the first mitosis ensued. During the second cell cycle, approximately 61% of the embryos were at the two-cell stage, with a monopolar spindle in each blastomere; that treatment was effective was based on second cleavage blockage. Approximately 15% of the eggs still remained at the one-cell stage and had a monopolar spindle (treatment was effective, according to the general model of first cleavage blockage). However, treatment was ineffective in approximately 15% of the embryos (bipolar spindle in each blastomeres) and in another 8% (bipolar spindle in one of the two blastomeres and a monopolar spindle in the other; both mechanisms operating in different parts of the embryo). This is the first report elucidating mitotic gynogenetic diploid induction by hydrostatic pressure in marine fishes and provides a cytological basis for developing an efficient method of inducing mitotic gynogenesis in olive flounder. (C) 2007 Elsevier Inc. All rights reserved.