Cortactin releases the brakes in actin- based motility by enhancing WASP-VCA detachment from Arp2/3 branches

Cortactin is involved in invadopodia and podosome formation [1], pathogens and endosome motility [2], and persistent lamellipodia protrusion [ [3] and [4] ]; its overexpression enhances cellular motility and metastatic activity [ [5] , [6] , [7] and [8] ]. Several mechanisms have been proposed to explain cortactin's role in Arp2/3-driven actin polymerization [ [9] and [10] ], yet its direct role in cell movement remains unclear. We use a biomimetic system to study the mechanism of cortactin-mediated regulation of actin-driven motility [11]. We tested the role of different cortactin variants that interact with Arp2/3 complex and actin filaments distinctively. We show that wild-type cortactin significantly enhances the bead velocity at low concentrations. Single filament experiments show that cortactin has no significant effect on actin polymerization and branch stability, whereas it strongly affects the branching rate driven by Wiskott-Aldrich syndrome protein (WASP)-VCA fragment and Arp2/3 complex. These results lead us to propose that cortactin plays a critical role in translating actin polymerization at a bead surface into motion, by releasing WASP-VCA from the new branching site. This enhanced release has two major effects: it increases the turnover rate of branching per WASP molecule, and it decreases the friction-like force caused by the binding of the moving surface with respect to the growing actin network.     

Cardinal directions for visual optic flow.

As we move through our environment, the flow of deforming images on the retinae provides a rich source of information about the three-dimensional structure of the external world and how to navigate through it. Recent evidence from psychophysical [1] [2] [3] [4], electrophysiological [5] [6] [7] [8] [9] and imaging [10] [11] studies suggests that there are neurons in the primate visual system - in the medial superior temporal cortex - that are specialised to respond to this type of complex 'optic flow' motion. In principle, optic flow could be encoded by a small number of neural mechanisms tuned to 'cardinal directions', including radial and circular motion [12] [13]. There is little support for this idea at present, however, from either physiological [6] [7] or psychophysical [14] research. We have measured the sensitivity of human subjects for detection of motion and for discrimination of motion direction over a wide and densely sampled range of complex motions. Average sensitivity was higher for inward and outward radial movement and for both directions of rotation, consistent with the existence of detectors tuned to these four types of motion. Principle component analysis revealed two clear components, one for radial stimuli (outward and inward) and the other for circular stimuli (clockwise and counter-clock-wise). The results imply that the mechanisms that analyse optic flow in humans tend to be tuned to the cardinal axes of radial and rotational motion.     

Environmentally constrained mutation and adaptive evolution in Salmonella

The relationship between environment and mutation is complex [1]. Claims of Lamarkian mutation [2] have proved unfounded [3], [4] and [5]; it is apparent, however, that the external environment can influence the generation of heritable variation, through either direct effects on DNA sequence [6] or DNA maintenance and copying mechanisms [7], [8], [9] and [10], or as a consequence of evolutionary processes [11], [12], [13], [14], [15] and [16]. The spectrum of mutational events subject to environmental influence is unknown [6] and precisely how environmental signals modulate mutation is unclear. Evidence from bacteria suggests that a transient recombination-dependent hypermutational state can be induced by starvation [5]. It is also apparent that chnages in the mutability of specific loci can be influenced by alterations in DNA topology [10] and [17]. Here we describe a remarkable instance of adaptive evolution in Salmonella which is caused by a mutation that occurs in intermediate-strength osmotic environments. We show that the mutation is not ‘directed’ and describe its genetic basis. We also present compelling evidence in support of the hypothesis that the mutational event is constrained by signals transmitted from the external environment via changes in the activity of DNA gyrase.     

Torque generation by one of the motor subunits of heterotrimeric kinesin-2

Heterotrimeric kinesin-2 motors [1] and [2] transport intraflagellar transport (IFT)-particles from the base to the tip of the axoneme to assemble and maintain cilia [3], [4], [5], [6], [7], [8], [9] and [10]. These motors are distinct in containing two non-identical motor subunits together with an accessory subunit [1], [11], [12], [13], [14] and [15]. We evaluated the significance of this organization by comparing purified wild type kinesin-2 holoenzymes that support IFT in vivo, with mutant trimers containing only one type of motor domain that do not support IFT in vivo. In motility assays, wild type kinesin-2 moved microtubules (MTs) at a rate intermediate between the rates supported by the two mutants. Interestingly, one of the mutants, but not the other mutant or the wild type protein, was observed to drive a persistent counter-clock-wise rotation of the gliding MTs. Thus one of the two motor domains of heterotrimeric kinesin-2 exerts torque as well as axial force as it moves along a MT, which may allow kinesin-2 to control its circumferential position around a MT doublet within the cilium.     

Local Interactions Lead to Pathogen-Driven Change to Host Population Dynamics

Individuals tend to interact more strongly with nearby individuals or within particular social groups. Recent theoretical advances have demonstrated that these within-population relationships can have fundamental implications for ecological and evolutionary dynamics [1], [2], [3], [4], [5], [6], [7], [8], [9], [10] and [11]. In particular, contact networks are crucial to the spread [12], [13] and [14] and evolution [8], [9], [11] and [15] of disease. However, the theory remains largely untested experimentally [16]. Here, we manipulate habitat viscosity and thereby the frequency of local interactions in an insect-pathogen model system in which the virus had previously been shown to have little effect on host population dynamics [16] and [17]. At high viscosity, the pathogen caused the collapse of dominant and otherwise stable host generation cycles. Modeling shows that this collapse can be explained by an increase in the frequency of intracohort interactions relative to intercohort interactions, leading to more disease transmission. Our work emphasizes that spatial structure can subtly mediate intraspecific competition and the effects of natural enemies. A decrease in dispersal in a population may actually (sometimes rather counterintuitively) intensify the effects of parasites. Broadly, because anthropological and environmental change often cause changes in population mixing, our work highlights the potential for dramatic changes in the effects of parasites on host populations.     

Targeted disruption of the gene encoding DNA ligase IV leads to lethality in embryonic mice

DNA ligase IV is the most recently identified member of a family of enzymes joining DNA strand breaks in mammalian cell nuclei [1] and [2]. The enzyme occurs in a complex with the XRCC4 gene product [3], an interaction mediated via its unique carboxyl terminus [4] and [5]. Cells lacking XRCC4 are hypersensitive to ionising radiation and defective in V(D)J recombination [3] and [6], implicating DNA ligase IV in the pathway of nonhomologous end-joining (NHEJ) of DNA double-strand breaks mediated by XRCC4, the Ku70/80 heterodimer and the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) in mammalian cells (reviewed in [7]). The phenotype of a null mutant of the Saccharomyces cerevisiae DNA ligase IV homologue indicates that the enzyme is non-essential and functions in yeast NHEJ [8], [9] and [10]. Unlike other mammalian DNA ligases for which cDNAs have been characterised, DNA ligase IV is encoded by an intronless gene (LIG4). Here, we show that targeted disruption of LIG4 in the mouse leads to lethality associated with extensive apoptotic cell death in the embryonic central nervous system. Thus, unlike Ku70/80 and DNA-PKcs [11], [12], [13] and [14], DNA ligase IV has an essential function in early mammalian development.     

Multistep Brownian dynamics: application to short wormlike chains

Brownian dynamics simulations of short wormlike chains are carried out using the method of Ermak and McCammon [(1978) J. Chem. Phys. 69 , 1352–1360]. Following Hagerman and Zimm [(1981) Biopolymers 20 , 1481–1502], the wormlike chain is modeled as a string of beads. In each simulation, the dynamic evolution of an ensemble of 100 randomly generated chains is calculated for a period of from 3 to 200 ns. Two different “experiments,” fluorescence depolarization and dynamic light scattering, were performed in these simulations. Since we are primarily interested in the bending motions and not the torsional motions in this work, we have placed the transition moments along the local symmetry axis of the wormlike chain in the fluorescence depolarization “experiment.” As predicted by the Barkley and Zimm theory [(1979) J. Chem. Phys. 70 , 2991–3008], a considerable amount of rapid bending motion was detected by fluorescence depolarization, though not as much as predicted by theory. We conclude that these differences are primarily due to differences between the model used in the theory and the simulations. The light-scattering experiment was found to be insensitive to internal motion in the low scattering angle limit.     

Modelling Diffusion in Zeolites by Molecular Dynamics Simulations

Abstract

The diffusion of molecules sorbed in zeolites is of growing interest for understanding the mechanisms of chemical processes with regard to selectivity and reactivity [1].

MD simulations give insight into physical systems on the molecular level allowing to study and visualize the motion of molecules even beyond the possibilities of experiments [2,3]. Single system parameters can easily be varied to study their influence, also those parameters that are fixed in reality (e.g., the size of particles). We present a cross section of our recent work to illustrate the capabilities of MD: The self diffusion coefficients (D) of a mixture of methane and xenon in silicalite show remarkable deviations from those of the pure species. This is shown and confirmed by PFG NMR experiments [4].

Simulating ethane in zeolite A the mechanism of diffusion has been studied. The effects of rotation on the diffusion lead to cases where D decreases with growing temperature [5].

The independence of self diffusion on lattice vibrations is proven even for zeolites with windows of guest particle size comparing simulations with rigid and vibrating zeolite lattice [6].     

Increased work in cardiac trabeculae causes decreased mitochondrial NADH fluorescence followed by slow recovery.

The oxidative phosphorylation rate in isolated mitochondria is stimulated by increased [ADP], resulting in decreased [NADH]. In intact hearts, however, increased mechanical work has generally not been shown to cause an increase in [ADP]. Therefore, increased [NADH] has been suggested as an alternative for stimulating the phosphorylation rate. Such a rise in [NADH] could result from stimulation of various substrate dehydrogenases by increased intracellular [Ca2+] (e.g., during increased pacing frequency). We have monitored mitochondrial [NADH] in isolated rat ventricular trabeculae, using a novel fluorescence spectroscopy method where a native fluorescence signal was used to correct for motion artifacts. Work was controlled by increased pacing frequency and assessed using time-averaged force. At low-pacing rates (approximately 0.1 Hz), [NADH] immediately decreased during contraction and then slowly recovered (approximately 5 s) before the next contraction. At higher rates, [NADH] initially decreased by an amount related to pacing rate (i.e., work). However, during prolonged stimulation, [NADH] slowly (approximately 60 s) recovered to a new steady-state level below the initial level. We conclude that 1) during increased work, oxidative phosphorylation is not initially stimulated by increased mitochondrial [NADH]; and 2) increased pacing frequency slowly causes stimulation of NADH production.     

The symmetric and asymmetric thiophene-fused benzocarborane: structures and first hyperpolarizabilities

The unusual properties of thiophene-fused benzocarborane have attracted a lot of interest in recent years due to their wide applications in photonics and optoelectronics. In the present work, nine molecules [M, N] (M, N are labeled as the number of thiophene rings on the left and right part, respectively) on the basis of thiophene-fused benzocarborane were considered. The first hyperpolarizability (β _tot) values of three synthesized symmetric molecules [1, 1], [2, 2], [3, 3] (M=N, Chem. Eur. J 2012. 18, 11251–11257) and six asymmetric molecules [1, 2], [1, 3], [1, 4], [1, 5], [2, 3], [2, 4] (M≠N) were investigated, β _tot values of symmetric molecules show the order: 39 of [1, 1]< 800 of [2, 2]< 903 au of [3, 3], which indicate that β _tot value increases with increasing the number of thiophene ring for symmetric molecules. The other order of β _tot values can be observed: 39 of [1, 1]< 800 of [1, 2]< 3553 of [1, 3]< 7998 of [1, 4]< 13049 au of [1, 5] and 66 of [2, 2]< 3240 of [2, 3]< 8029 au of [2, 4]. Interestingly, when sum of M and N is constant, larger difference between M and N is, larger β _tot value is: 800 au of [2, 2]< 3553 au of [1, 3]; 3240 au of [2, 3] < 7998 au of [1, 4]; 903 au of [3, 3]< 8029 au of [2, 4]< 13049 au of [1, 5]. Significantly, [1, 5] with six thiophene rings has the largest β _tot value (13049 au) which is greatly larger than 903 au of [3, 3] with six thiophene rings. Furthermore, the natural bond orbital (NBO) charge populations, the nucleus-independent chemical shift (NICS), the bond length alternation (BLA) of the nine molecules and crucial transition were studied in our work. We hope that the present work will be beneficial for future theoretical and experimental studies on the electro-optical properties of thiophene-fused benzocarborane molecules.

cis-Inhibition of Notch by Endogenous Delta Biases the Outcome of Lateral Inhibition

Lateral inhibition mediated by Delta/Notch (Dl/N) signaling is used throughout development to limit the number of initially equivalent cells that adopt a particular fate [1], [2] and [3]. Although adjacent cells express both Dl ligand and N receptor, signaling between them ultimately occurs in only one direction. Classically, this has been explained entirely by feedback: activated N can downregulate Dl, amplifying even slight asymmetries in the Dl or N activities of adjacent cells [1], [2], [3], [4] and [5]. Here, however, we present an example of lateral inhibition in which unidirectional signaling depends instead on Dl's ability to inhibit N within the same cell, a phenomenon known as cis-inhibition [6], [7], [8], [9], [10] and [11]. By genetically manipulating individual R1/R6/R7 photoreceptor precursors in the Drosophila eye, we show that loss of Dl-mediated cis-inhibition reverses the direction of lateral signaling. Based on our finding that Dl in R1/R6s requires endocytosis to trans-activate but not to cis-inhibit N, we reexamine previously published data from other examples of lateral inhibition. We conclude that cis-inhibition generally influences the direction of Dl/N signaling and should therefore be included in standard models of lateral inhibition.     

Begomoviruses Associated with Yellow Leaf Curl Disease of Tomato in Iran*

The occurrence of Tomato yellow leaf curl virus (TYLCV; genus Begomovirus, family Geminiviridae) in the major tomato‐growing areas of Iran was determined using TAS‐ELISA and PCR. The nucleotide sequences of the coat protein (CP) gene and intergenic region (IR) of eight Iranian isolates were determined. CP nucleotide identities among the Iranian isolates were 96–98%, and showed 94–96% identity with TYLCV‐IR [IR:Ira:98] and TYLCV‐IL [IL:Reo:86]. However, they showed low identity (68–69%) with ToLCIRV‐[IR:Ira]. Sequence analyses of IR indicated that seven Iranian isolates had sequence identity of 93–100% with each other, and 76% identity with the Jiroft isolate; identities of 75–79% with TYLCV‐IR[IR:Ira:98] were observed in every case, and 59–62% identity with ToLCIRV‐[IR:Ira]. The IR nucleotide sequences of Iranian isolates showed 92–93% identity with TYLCV‐IL[IL:Reo:86], except the Jiroft isolate (75%). The CP and IR sequence analyses suggested that eight Iranian TYLCV isolates probably differ from ToLCIRV‐[IR:Ira]. Based on IR sequence comparisons and phylogenetic analyses, the Iranian isolates were divided into two groups. The first major group (A), consists of seven virus isolates, was most closely related to TYLCV‐IL[IL:Reo:86], and relatively divergent from TYLCV‐IR [IR:Ira:98] and ToLCIRV‐[IR:Ira]. However, the Jiroft isolate from group B did not show high similarity with TYLCV‐IR[IR:Ira:98], ToLCIRV‐[IR:Ira], and TYLCV‐IL[IL:Reo:86], suggesting that the isolate may be a divergent variant. The differences are in a range that suggests different strains or species from TYLCV‐IR[IR:Ira:98] and ToLCIRV‐[IR:Ira] are probably associated with tomato yellow leaf curl disease in Iran.     

Endogenous Glutamate Increases Extracellular Concentrations of Dopamine, GABA, and Taurine Through NMDA and AMPA/Kainate Receptors in Striatum of the Freely Moving Rat: A Microdialysis Study

Abstract: Interactions between glutamate (Glu), dopamine (DA), GABA, and taurine (Tau) were investigated in striatum of the freely moving rat by using microdialysis. Intrastriatal infusions of the selective Glu uptake inhibitor l - trans -pyrrolidine-3,4-dicarboxylic acid (PDC) were used to increase the endogenous extracellular [Glu]. Correlations between extracellular [Glu] and extracellular [DA], [GABA], and [Tau], and the effects of a selective blockade of ionotropic Glu receptors, were studied. PDC (1, 2, and 4 m M ) produced a dose-related increase in extracellular [Glu]. At the highest dose of PDC, [Glu] increased from 1.55 ± 0.35 to 6.11 ± 0.88 µ M . PDC also increased extracellular [DA], [GABA], and [Tau]. The increasing [Glu] was correlated significantly with increasing [DA], [GABA], and [Tau]. PDC also decreased extracellular concentrations of DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and 4-hydroxy-3-methoxyphenylacetic acid (HVA). Perfusion with the NMDA-receptor antagonist 3-[( R )-2-carboxypiperazin-4-yl]-propyl-1-phosphonic acid (1 m M ) or the AMPA/kainate-receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) (1 m M ) attenuated the increases produced by PDC (4 m M ) on [DA], [GABA], and [Tau], and decreases in [DOPAC] and [HVA]. DNQX also attenuated the increases in [Glu] induced by PDC. These data show that endogenous Glu plays a role in modulating the extracellular concentrations of DA, GABA, and Tau in striatum of the freely moving rat.     

Electron probe X-ray microanalysis of cellular ions in the eccrine secretory coil cells during methacholine stimulation

Summary Intracellular concentrations of Na, K, Cl ([Na], [K] and [Cl], respectively) and other elements were determined in isolated monkey eccrine sweat secretory coil cells using quantitative electron probe X-ray microanalysis of freeze dried cryosections. The validity of the methodology was partially supported by qualitative agreement of the X-ray microanalysis data with those obtained by micro-titration with a helium glow spectrophotometer. [Na], [K] and [Cl] of the cytoplasm were the same as those in the nucleus in both clear and dark cells. [Na], [K], and [Cl] of the clear cells were also the same as those of the dark cells at rest and after stimulation with methacholine (MCh), suggesting that these two cell types behave like a functional syncytium. MCh stimulation induced a pharmacologically specific, dose-dependent decrease in [K] and [Cl] (as much as 65%), and a 3.7-fold increase in [Na]. In myoepithelial cells, a similar change in [Na] and [K] was noted after MCh stimulation although the decrease in [Cl] was only 20%. The MCh-induced change in [Na], [K] and [Cl] was almost completely inhibited by removal of Ca²⁺ from the medium. 10^–4 m bumetanide inhibited the MCh-induced increase in [Na], reduced the decrease in [K] by about 50%, but slightly augmented the MCh-induced decrease in [Cl]. 10^–4 m ouabain increased [Na] and decreased [K] as did MCh; however, unlike MCh, ouabain increased [Cl] by 56% after 30 min of incubation. Thus the data may be best interpreted to indicate that Ca-dependent K efflux and (perhaps also Ca-dependent) Cl efflux are the predominat initial ionic movement in muscarinic cholinergic stimulation of the eccrine sweat secretory coils and that the ouabain-sensitive Na pump plays an important role in maintenance of intracellular ions and sweat secretion.     

Synergistic interactions between XPC and p53 mutations in double-mutant mice: neural tube abnormalities and accelerated UV radiation-induced skin cancer

The significance of DNA repair to human health has been well documented by studies on xeroderma pigmentosum (XP) patients, who suffer a dramatically increased risk of cancer in sun-exposed areas of their skin [1] and [2]. This autosomal recessive disorder has been directly associated with a defect in nucleotide excision–repair (NER) [1] and [2]. Like human XP individuals, mice carrying homozygous mutations in XP genes manifest a predisposition to skin carcinogenesis following exposure to ultraviolet (UV) radiation [3], [4] and [5]. Recent studies have suggested that, in addition to roles in apoptosis [6] and cell-cycle checkpoint control [7] in response to DNA damage, p53 protein may modulate NER [8]. Mutations in the p53 gene have been observed in 50% of all human tumors [9] and have been implicated in both the early [10] and late [11] stages of skin cancer. To examine the consequences of a combined deficiency of the XPC and the p53 proteins in mice, we generated double-mutant animals. We document a spectrum of neural tube defects in XPC p53 mutant embryos. Additionally, we show that, following exposure to UV-B radiation, XPC p53 mutant mice have more severe solar keratosis and suffer accelerated skin cancer compared with XPC mutant mice that are wild-type with respect to p53.     

Biosynthesis of p-hydroxybenzoic acid in poplar lignin

Biosynthetic pathways to p-hydroxybenzoic acid in polar lignin were examined by tracer experiments. High incorporation of radioactivity to the acid was observed when shikimic acid-[1-¹⁴C], phenylalanine-[3-¹⁴C], trans-cinnamic acid-[3-¹⁴C], p-coumaric acid-[3-¹⁴C] and p-hydroxybenzoic acid-[COOH-¹⁴C] were administered, while incorporation was low from shikimic acid-[COOH-¹⁴C], phenylalanine-[1-¹⁴C], phenylalanine-[2-¹⁴C], tyrosine-[3-¹⁴C], benzoic acid-[COOH-¹⁴C], sodium acetate-[1-¹⁴C] and d-glucose-[U-¹⁴C]. Thus p-hydroxybenzoic acid in poplar lignin is formed mainly via the pathway: shikimic acid → phenylalanine → trans-cinnamic acid → p-coumaric acid → p-hydroxybenzoic acid.     

Compatibility of magnetic imprinting and secular variation

Diverse ocean migrants, including some sea turtles, elephant seals, and salmon, begin life in particular reproductive areas along coastlines, disperse across vast expanses of sea, and then return as adults to their natal areas to reproduce [1], [2] and [3]. Little is known about how such marine animals guide themselves to the correct coastal region from hundreds or thousands of kilometers away and after absences ranging in duration from a few months to a decade or more. One hypothesis is that animals imprint on the magnetic field of their home area and use this information to return [1]. The Earth's field varies predictably across the globe, so different geographic areas are marked by distinctive magnetic fields that might, in principle, provide unique magnetic signatures for natal areas [4]. A potentially serious complication for this hypothesis is that the Earth's field changes gradually over time [1] and [4], causing the magnetic signatures that define natal areas to slowly drift. This secular variation could make natal homing via magnetic imprinting impossible if the magnetic signatures moved too far from the natal area [1], [5] and [6]. To investigate whether magnetic imprinting is compatible with secular variation, we sought a species with a life history that poses challenges for the hypothesis, reasoning that if magnetic imprinting is consistent with natal homing under unfavorable circumstances, then it would also be plausible in most other cases. We chose the Kemp's ridley sea turtle (Lepidochelys kempii), an endangered species that ranges widely over the Gulf of Mexico, northern Caribbean, and the eastern U.S. coast, but returns to nest along a single, limited region of coastline in northern Mexico [7]. This species requires approximately 10–15 years to reach sexual maturity [7] and is thus absent from its natal area for much longer than animals such as salmon and elephant seals [2] and [3]. Given this long absence, the Kemp's ridley appears to be particularly susceptible to effects of secular variation if it relies on magnetic imprinting. The modeling results we report here show that the magnetic imprinting hypothesis can account for how the Kemp's ridley turtle returns to its natal region even after absences of a decade or more.