A pharmacological cocktail for arresting actin dynamics in living cells.

The actin cytoskeleton is regulated by factors that influence polymer assembly, disassembly, and network rearrangement. Drugs that inhibit these events have been used to test the role of actin dynamics in a wide range of cellular processes. Previous methods of arresting actin rearrangements take minutes to act and work well in some contexts, but can lead to significant actin reorganization in cells with rapid actin dynamics, such as neutrophils. In this paper, we report a pharmacological cocktail that not only arrests actin dynamics but also preserves the structure of the existing actin network in neutrophil-like HL-60 cells, human fibrosarcoma HT1080 cells, and mouse NIH 3T3 fibroblast cells. Our cocktail induces an arrest of actin dynamics that initiates within seconds and persists for longer than 10 min, during which time cells maintain their responsivity to external stimuli. With this cocktail, we demonstrate that actin dynamics, and not simply morphological polarity or actin accumulation at the leading edge, are required for the spatial persistence of Rac activation in HL-60 cells. Our drug combination preserves the structure of the existing cytoskeleton while blocking actin assembly, disassembly, and rearrangement, and should prove useful for investigating the role of actin dynamics in a wide range of cellular signaling contexts

Anyon Wave Function for the Fractional Quantum Hall Effect

An anyon wave function (characterized by the statistical factor $n$) projected onto the lowest Landau level is derived for the fractional quantum Hall effect states at filling factor $\nu = n/(2pn+1)$ ($p$ and $n$ are integers). We study the properties of the anyon wave function by using detailed Monte Carlo simulations in disk geometry and show that the anyon ground-state energy is a lower bound to the composite fermion one.Comment: Reference adde

Apparent phonon side band modes in pi-conjugated systems: polymers, oligomers and crystals

The emission spectra of many pi-conjugated polymers and oligomers contain side-band replicas with apparent frequencies that do not match the Raman active mode frequencies. Using a time dependent model we show that in such many mode systems, the increased damping of the time dependent transition dipole moment correlation function results in an effective elimination of the vibrational modes from the emission spectrum; subsequently causing the appearance of a regularly spaced progression at a new apparent frequency. We use this damping dependent vibrational reshaping to quantitatively account for the vibronic structure in the emission spectra of pi-conjugated systems in the form of films, dilute solutions and single crystals. In particular, we show that by using the experimentally measured Raman spectrum we can account in detail for the apparent progression frequencies and their relative intensities in the emission spectrum.Comment: Presented in "Optical Probes 2005", Bangalore, Indi

Longidorus israelensis sp. n. (Nematoda : Dorylaimoidea), a parasite of carrot in Israel

#Longidorus israelensis sp. n., espèce parthénogénétique associée à des dégâts sur carotte en Israël, est décrite. Cette espèce est caractérisée par une grande longueur du corps (7,1-9,1 mm), une région labiale légèrement en relief et aplatie frontalement, des poches amphidiennes non bilobées, un long odontostyle (125-135 micromètres) et une queue courte, sub-hémisphérique (36-46 micromètres). Elle présente également une disposition inhabituelle des noyaux des glandes oesophagiennes. Les carottes attaquées par #L. israelensis sp. n. voient la croissance de leurs racines stoppée, le départ de racines secondaires et l'apparition de renflements à l'extrémité des racines. Il en résulte des carottes déformées et divisées en pluseiurs parties. Le nématode est généralement rencontré à des profondeurs du sol variant de 20 à 40 cm mais il peut migrer jusqu'à 40-100 cm de profondeur de façon à survivre pendant la période estivale chaude et sèche. (Résumé d'auteur

Reversible Optogenetic Control of Subcellular Protein Localization in a Live Vertebrate Embryo.

We demonstrate the utility of the phytochrome system to rapidly and reversibly recruit proteins to specific subcellular regions within specific cells in a living vertebrate embryo. Light-induced heterodimerization using the phytochrome system has previously been used as a powerful tool to dissect signaling pathways for single cells in culture but has not previously been used to reversibly manipulate the precise subcellular location of proteins in multicellular organisms. Here we report the experimental conditions necessary to use this system to manipulate proteins in vivo. As proof of principle, we demonstrate that we can manipulate the localization of the apical polarity protein Pard3 with high temporal and spatial precision in both the neural tube and the embryo's enveloping layer epithelium. Our optimizations of optogenetic component expression and chromophore purification and delivery should significantly lower the barrier for establishing this powerful optogenetic system in other multicellular organisms