Identification of secretory granule phosphatidylinositol 4,5-bisphosphateinteracting proteins using an affinity pulldown strategy

Phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P-2) synthesis is required for calcium-dependent exocytosis in neurosecretory cells. We developed a PtdIns(4,5)P-2 bead pulldown strategy combined with subcellular fractionation to identify endogenous chromaffin granule proteins that interact with PtdIns(4,5)P-2. We identified two synaptotagmin isoforms, synaptotagmins 1 and 7; spectrin; alpha-adaptin; and synaptotagmin-like protein 4 (granuphilin) by mass spectrometry and Western blotting. The interaction between synaptotagmin 7 and PtdIns(4,5)P-2 and its functional relevance was investigated. The 45-kDa isoform of synaptotagmin 7 was found to be highly expressed in adrenal chromaffin cells compared with PC12 cells and to mainly localize to secretory granules by subcellular fractionation, immunoisolation, and immunocytochemistry. We demonstrated that synaptotagmin 7 binds PtdIns(4,5)P-2 via the C2B domain in the absence of calcium and via both the C2A and C2B domains in the presence of calcium. We mutated the polylysine stretch in synaptotagmin 7 C2B and demonstrated that this mutant domain lacks the calcium-independent PtdIns(4,5)P-2 binding. Synaptotagmin 7 C2B domain inhibited catecholamine release from digitonin-permeabilized chromaffin cells, and this inhibition was abrogated with the C2B polylysine mutant. These data indicate that synaptotagmin 7 C2B-effector interactions, which occur via the polylysine stretch, including calcium-independent PtdIns(4,5)P-2 binding, are important for chromaffin granule exocytosis

Control over phase separation and nucleation using a laser-tweezing potential

Control over the nucleation of new phases is highly desirable but elusive. Even though there is a long history of crystallization engineering by varying physicochemical parameters, controlling which polymorph crystallizes or whether a molecule crystallizes or forms an amorphous precipitate is still a poorly understood practice. Although there are now numerous examples of control using laser-induced nucleation, the absence of physical understanding is preventing progress. Here we show that the proximity of a liquid–liquid critical point or the corresponding binodal line can be used by a laser-tweezing potential to induce concentration gradients. A simple theoretical model shows that the stored electromagnetic energy of the laser beam produces a free-energy potential that forces phase separation or triggers the nucleation of a new phase. Experiments in a liquid mixture using a low-power laser diode confirm the effect. Phase separation and nucleation using a laser-tweezing potential explains the physics behind non-photochemical laser-induced nucleation and suggests new ways of manipulating matter

The 2021 outburst of the recurrent nova RS Ophiuchi observed in X-rays by the Neil Gehrels Swift Observatory: a comparative study

On 2021 August 8, the recurrent nova RS Ophiuchi erupted again, after an interval of 15.5 yr. Regular monitoring by the Neil Gehrels Swift Observatory began promptly, on August 9.9 (0.37 day after the optical peak), and continued until the source passed behind the Sun at the start of November, 86 days later. Observations then restarted on day 197, once RS Oph emerged from the Sun constraint. This makes RS Oph the first Galactic recurrent nova to have been monitored by Swift throughout two eruptions. Here we investigate the extensive X-ray datasets from 2006 and 2021, as well as the more limited data collected by EXOSAT in 1985. The hard X-rays arising from shock interactions between the nova ejecta and red giant wind are similar following the last two eruptions. In contrast, the early super-soft source (SSS) in 2021 was both less variable and significantly fainter than in 2006. However, 0.3–1 keV light-curves from 2021 reveal a 35 s quasi-periodic oscillation consistent in frequency with the 2006 data. The Swift X-ray spectra from 2021 are featureless, with the soft emission typically being well parametrized by a simple blackbody, while the 2006 spectra showed much stronger evidence for superimposed ionized absorption edges. Considering the data after day 60 following each eruption, during the supersoft phase the 2021 spectra are hotter, with smaller effective radii and lower wind absorption, leading to an apparently reduced bolometric luminosity. We explore possible explanations for the gross differences in observed SSS behaviour between the 2006 and 2021 outbursts

Additive growth inhibitory effects of ibandronate and antiestrogens in estrogen receptor-positive breast cancer cell lines

INTRODUCTION: Bisphosphonates are inhibitors of osteoclast-mediated tumor-stimulated osteolysis, and they have become standard therapy for the management of bone metastases from breast cancer. These drugs can also directly induce growth inhibition and apoptosis of osteotropic cancer cells, including estrogen receptor-positive (ER+) breast cancer cells. METHODS: We examined the anti-proliferative properties of ibandronate on two ER+ breast cancer cell lines (MCF-7 and IBEP-2), and on one ER negative (ER-) cell line (MDA-MB-231). Experiments were performed in steroid-free medium to assess ER regulation and the effect of ibandronate in combination with estrogen or antiestrogens. RESULTS: Ibandronate inhibited cancer cell growth in a dose- and time-dependent manner (approximate IC(50): 10(-4 )M for MCF-7 and IBEP-2 cells; 3 × 10(-4 )M for MDA-MB-231 cells), partly through apoptosis induction. It completely abolished the mitogenic effect induced by 17β-estradiol in ER+ breast cancer cells, but affected neither ER regulation nor estrogen-induced progesterone receptor expression, as documented in MCF-7 cells. Moreover, ibandronate enhanced the growth inhibitory action of partial (4-hydroxytamoxifen) and pure (ICI 182,780, now called fluvestrant or Faslodex™) antiestrogens in estrogen-sensitive breast cancer cells. Combination analysis identified additive interactions between ibandronate and ER antagonists. CONCLUSION: These data constitute the first in vitro evidence for additive effects between ibandronate and antiestrogens, supporting their combined use for the treatment of bone metastases from breast cancer

Lambda and Antilambda polarization from deep inelastic muon scattering

We report results of the first measurements of Lambda and Antilambda polarization produced in deep inelastic polarized muon scattering on the nucleon. The results are consistent with an expected trend towards positive polarization with increasing x_F. The polarizations of Lambda and Antilambda appear to have opposite signs. A large negative polarization for Lambda at low positive x_F is observed and is not explained by existing models.A possible interpretation is presented.Comment: 9 pages, 2 figure

Representation of Time-Varying Stimuli by a Network Exhibiting Oscillations on a Faster Time Scale

Sensory processing is associated with gamma frequency oscillations (30–80 Hz) in sensory cortices. This raises the question whether gamma oscillations can be directly involved in the representation of time-varying stimuli, including stimuli whose time scale is longer than a gamma cycle. We are interested in the ability of the system to reliably distinguish different stimuli while being robust to stimulus variations such as uniform time-warp. We address this issue with a dynamical model of spiking neurons and study the response to an asymmetric sawtooth input current over a range of shape parameters. These parameters describe how fast the input current rises and falls in time. Our network consists of inhibitory and excitatory populations that are sufficient for generating oscillations in the gamma range. The oscillations period is about one-third of the stimulus duration. Embedded in this network is a subpopulation of excitatory cells that respond to the sawtooth stimulus and a subpopulation of cells that respond to an onset cue. The intrinsic gamma oscillations generate a temporally sparse code for the external stimuli. In this code, an excitatory cell may fire a single spike during a gamma cycle, depending on its tuning properties and on the temporal structure of the specific input; the identity of the stimulus is coded by the list of excitatory cells that fire during each cycle. We quantify the properties of this representation in a series of simulations and show that the sparseness of the code makes it robust to uniform warping of the time scale. We find that resetting of the oscillation phase at stimulus onset is important for a reliable representation of the stimulus and that there is a tradeoff between the resolution of the neural representation of the stimulus and robustness to time-warp. Author Summary Sensory processing of time-varying stimuli, such as speech, is associated with high-frequency oscillatory cortical activity, the functional significance of which is still unknown. One possibility is that the oscillations are part of a stimulus-encoding mechanism. Here, we investigate a computational model of such a mechanism, a spiking neuronal network whose intrinsic oscillations interact with external input (waveforms simulating short speech segments in a single acoustic frequency band) to encode stimuli that extend over a time interval longer than the oscillation's period. The network implements a temporally sparse encoding, whose robustness to time warping and neuronal noise we quantify. To our knowledge, this study is the first to demonstrate that a biophysically plausible model of oscillations occurring in the processing of auditory input may generate a representation of signals that span multiple oscillation cycles.National Science Foundation (DMS-0211505); Burroughs Wellcome Fund; U.S. Air Force Office of Scientific Researc

The influence of technology on the mathematical modelling of physical phenomena

A study is presented in which students are asked to model two physical phenomena using applications on electronic tablets : a bounce of a ball and the extension of a spring. The analysis focusses on (a) the influence of characteristics of the applications on the tablets on the decisions that groups of 16-year-old students made during the modelling phases in which reality and mathematics are related, (b) mathematisation of the phenomena and (c) interpretation of the models. The phenomena were recorded using an app that requests users establish a set of references during the mathematisation process, which makes students focus on the way the references have been set to interpret the model properly. Our findings indicated inconsistences between student decisions made during mathematisation and their considerations during interpretation of the model. To conclude we suggest reasons students experience problems in working without a pre-defined reference syste

Swift detection of the super-swift switch-on of the super-soft phase in nova V745 Sco (2014)

V745 Sco is a recurrent nova, with the most recent eruption occurring in February 2014. V745 Sco was first observed by Swift a mere 3.7 hr after the announcement of the optical discovery, with the super-soft X-ray emission being detected around four days later and lasting for only ~two days, making it both the fastest follow-up of a nova by Swift and the earliest switch-on of super-soft emission yet detected. Such an early switch-on time suggests a combination of a very high velocity outflow and low ejected mass and, together with the high effective temperature reached by the super-soft emission, a high mass white dwarf (>1.3 M_sun). The X-ray spectral evolution was followed from an early epoch where shocked emission was evident, through the entirety of the super-soft phase, showing evolving column density, emission lines, absorption edges and thermal continuum temperature. UV grism data were also obtained throughout the super-soft interval, with the spectra showing mainly emission lines from lower ionization transitions and the Balmer continuum in emission. V745 Sco is compared with both V2491 Cyg (another nova with a very short super-soft phase) and M31N 2008-12a (the most rapidly recurring nova yet discovered). The longer recurrence time compared to M31N 2008-12a could be due to a lower mass accretion rate, although inclination of the system may also play a part. Nova V745 Sco (2014) revealed the fastest evolving super-soft source phase yet discovered, providing a detailed and informative dataset for study

Macro-Climatic Distribution Limits Show Both Niche Expansion and Niche Specialization among C4 Panicoids

Grasses are ancestrally tropical understory species whose current dominance in warm open habitats is linked to the evolution of C4 photosynthesis. C4 grasses maintain high rates of photosynthesis in warm and water stressed environments, and the syndrome is considered to induce niche shifts into these habitats while adaptation to cold ones may be compromised. Global biogeographic analyses of C4 grasses have, however, concentrated on diversity patterns, while paying little attention to distributional limits. Using phylogenetic contrast analyses, we compared macro-climatic distribution limits among ~1300 grasses from the subfamily Panicoideae, which includes 4/5 of the known photosynthetic transitions in grasses. We explored whether evolution of C4 photosynthesis correlates with niche expansions, niche changes, or stasis at subfamily level and within the two tribes Paniceae and Paspaleae. We compared the climatic extremes of growing season temperatures, aridity, and mean temperatures of the coldest months. We found support for all the known biogeographic distribution patterns of C4 species, these patterns were, however, formed both by niche expansion and niche changes. The only ubiquitous response to a change in the photosynthetic pathway within Panicoideae was a niche expansion of the C4 species into regions with higher growing season temperatures, but without a withdrawal from the inherited climate niche. Other patterns varied among the tribes, as macro-climatic niche evolution in the American tribe Paspaleae differed from the pattern supported in the globally distributed tribe Paniceae and at family level.Fil: Aagesen, Lone. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Botánica Darwinion. Academia Nacional de Ciencias Exactas, Físicas y Naturales. Instituto de Botánica Darwinion; ArgentinaFil: Biganzoli, Fernando. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bena, María Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Botánica Darwinion. Academia Nacional de Ciencias Exactas, Físicas y Naturales. Instituto de Botánica Darwinion; ArgentinaFil: Godoy Bürki, Ana Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Botánica Darwinion. Academia Nacional de Ciencias Exactas, Físicas y Naturales. Instituto de Botánica Darwinion; ArgentinaFil: Reinheimer, Renata. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; ArgentinaFil: Zuloaga, Fernando Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Botánica Darwinion. Academia Nacional de Ciencias Exactas, Físicas y Naturales. Instituto de Botánica Darwinion; Argentin