New nucleic dyes for pico-and nanoplankton cytometric analysis

Flow cytometry (FCM) is a promising tool in the field of aquatic phytoplankton ecology because it allows for multi-parameter assessment of the physiological state of individual cells in an algal population. It can help to elucidate major questions such as phytoplankton taxa identification, the evaluation of cell quantity and viability, and the measuring of phytoplankton and general microbial metabolic activities. Traditionally, microalgal characterization is performed by microscopic analysis using UV-excited nuclear dyes (e.g. Hoechst and DAPI) or dyes that are excited in the blue-green part of the spectrum such as propidium iodide and eosin. The development of multi-laser cytometric systems has widened the possibilities for multi-parametric analysis and cell sorting of phytoplankton populations. Notwithstanding, significant algae autofluorescence originating from different types of chlorophyll and accessory pigments may overlap with propidium iodide and/or eosin staining and affect the resolution of algae clusters and cell sorting

A substorm in midnight auroral precipitation

International audienceDMSP F7 spacecraft observations for the whole of 1986 were used to construct the empirical model of the midnight auroral precipitation during a substorm. The model includes the dynamics of different auroral precipitation boundaries and simultaneous changes in average electron precipitation energy and energy flux in different precipitation regions during all substorm phases, as well as the IMF and solar wind plasma signatures during a substorm. The analysis of the model shows a few important features of precipitation. (1) During the magnetic quietness and just before the beginning of the substorm expansive phase the latitudinal width of the auroral precipitation in the nightside sector is about 5 ? 6° CGL, while that of the auroral oval is about 2 ? 3° CGL during such periods. (2) For about 5 min before the substorm onset a decrease in the average precipitating electron energy in the equatorward part of auroral zone was observed simultaneously, with an increase in both the average electron energy and energy flux of electron precipitation in the poleward part of the auroral zone. (3) The isotropy boundary position in the beginning of the substorm expansive phase coincides well with the inner edge of the central plasma sheet. The analysis of interplanetary medium parameters shows that, on average, during the substorm development, the solar wind dynamic pressure was about 1.5 times that of the magnetic quietness period. Substorms occurred predominantly during the southward IMF orientation, suggesting that substorm onset often was not associated with the northern turn or decrease in the southward interplanetary Bz . The Northern Hemisphere's substorms occurred generally during the positive interplanetary By in winter, and they were observed when the interplanetary By was negative in summer

Physical criterion of the degree of non-Markovity of relaxation processes in liquids

The microscopic parameter characterizing the degree of non-Markovity of irreversible processes is introduced. It is shown that the structure relaxation process in liquids is essentially non-Markovian in a wide range of wave vectors excluding the region near the first maximum of the static structure factor. © 1990

Optical Spin Orientation under Inter- and Intra-Subband Transitions in QWs

It is shown that absorption of circularly polarized infrared radiation achieved by inter-subband and intra-subband (Drude-like) transitions results in a monopolar spin orientation of free carriers. The monopolar spin polarization in zinc-blende-based quantum wells (QWs) is demonstrated by the observation of the spin-galvanic and circular photogalvanic effects. It is shown that monopolar spin orientation in n-type QWs becomes possible if an admixture of valence band states to the conduction band wave function and the spin-orbit splitting of the valence band are taken into account

New nucleic dyes for pico-and nanoplankton cytometric analysis

Flow cytometry (FCM) is a promising tool in the field of aquatic phytoplankton ecology because it allows for multi-parameter assessment of the physiological state of individual cells in an algal population. It can help to elucidate major questions such as phytoplankton taxa identification, the evaluation of cell quantity and viability, and the measuring of phytoplankton and general microbial metabolic activities. Traditionally, microalgal characterization is performed by microscopic analysis using UV-excited nuclear dyes (e.g. Hoechst and DAPI) or dyes that are excited in the blue-green part of the spectrum such as propidium iodide and eosin. The development of multi-laser cytometric systems has widened the possibilities for multi-parametric analysis and cell sorting of phytoplankton populations. Notwithstanding, significant algae autofluorescence originating from different types of chlorophyll and accessory pigments may overlap with propidium iodide and/or eosin staining and affect the resolution of algae clusters and cell sorting

Deterministic mechanical model of T-killer cell polarization reproduces the wandering of aim between simultaneously engaged targets

T-killer cells of the immune system eliminate virus-infected and tumorous cells through direct cell-cell interactions. Reorientation of the killing apparatus inside the T cell to the T-cell interface with the target cell ensures specificity of the immune response. The killing apparatus can also oscillate next to the cell-cell interface. When two target cells are engaged by the T cell simultaneously, the killing apparatus can oscillate between the two interface areas. This oscillation is one of the most striking examples of cell movements that give the microscopist an unmechanistic impression of the cell's fidgety indecision. We have constructed a three-dimensional, numerical biomechanical model of the molecular-motor-driven microtubule cytoskeleton that positions the killing apparatus. The model demonstrates that the cortical pulling mechanism is indeed capable of orienting the killing apparatus into the functional position under a range of conditions. The model also predicts experimentally testable limitations of this commonly hypothesized mechanism of T-cell polarization. After the reorientation, the numerical solution exhibits complex, multidirectional, multiperiodic, and sustained oscillations in the absence of any external guidance or stochasticity. These computational results demonstrate that the strikingly animate wandering of aim in T-killer cells has a purely mechanical and deterministic explanation. © 2009 Kim, Maly

Non-linear Dose Response of Lymphocyte Cell Lines to Microtubule Inhibitors

Microtubule (MT) inhibitors show anti-cancer activity in a wide range of tumors in vitro and demonstrate high clinical efficacy. To date they are routinely included into many chemotherapeutic regimens. While the mechanisms of MT inhibitors’ interactions with tubulin have been well-established, the relationship between their concentration and effect on neoplastic cells is not completely understood. The common notion is that tumor cells are most vulnerable during division and all MT inhibitors block them in mitosis and induce mitotic checkpoint-associated cell death. At the same time multiple evidence of more subtle effects of lower doses of MT inhibitors on cell physiology exist. The extent of efficacy of the low-dose MT inhibitor treatment and the mechanisms of resulting cell death currently present a critical issue in oncology. The prospect of MT inhibitor dose reduction is promising as protocols at higher concentration have multiple side effects. We assessed cell cycle changes and cell death induced by MT inhibitors (paclitaxel, nocodazole, and vinorelbine) on human lymphoid B-cell lines in a broad concentration range. All inhibitors had similar accumulation effects and demonstrated “trigger” concentrations that induce cell accumulation in G2/M phase. Concentrations slightly below the “trigger” promoted cell accumulation in sub-G1 phase. Multi-label analysis of live cells showed that the sub-G1 population is heterogeneous and may include cells that are still viable after 24 h of treatment. Effects observed were similar for cells expressing Tat-protein. Thus cell cycle progression and cell death are differentially affected by high and low MT inhibitor concentrations

Anisotropic coarse-grained statistical potentials improve the ability to identify native-like protein structures

We present a new method to extract distance and orientation dependent potentials between amino acid side chains using a database of protein structures and the standard Boltzmann device. The importance of orientation dependent interactions is first established by computing orientational order parameters for proteins with alpha-helical and beta-sheet architecture. Extraction of the anisotropic interactions requires defining local reference frames for each amino acid that uniquely determine the coordinates of the neighboring residues. Using the local reference frames and histograms of the radial and angular correlation functions for a standard set of non-homologue protein structures, we construct the anisotropic pair potentials. The performance of the orientation dependent potentials was studied using a large database of decoy proteins. The results demonstrate that the new distance and orientation dependent residue-residue potentials present a significantly improved ability to recognize native folds from a set of native and decoy protein structures.Comment: Submitted to "The Journal of Chemical Physics