Tracking autophagy during proliferation and differentiation of trypanosoma brucei

Autophagy is a lysosome-dependent degradation mechanism that sequesters target cargo into autophagosomal vesicles. The Trypanosoma brucei genome contains apparent orthologues of several autophagy-related proteins including an ATG8 family. These ubiquitin-like proteins are required for autophagosome membrane formation, but our studies show that ATG8.3 is atypical. To investigate the function of other ATG proteins, RNAi compatible T. brucei were modified to function as autophagy reporter lines by expressing only either YFP-ATG8.1 or YFP-ATG8.2. In the insect procyclic lifecycle stage, independent RNAi down-regulation of ATG3 or ATG7 generated autophagy-defective mutants and confirmed a pro-survival role for autophagy in the procyclic form nutrient starvation response. Similarly, RNAi depletion of ATG5 or ATG7 in the bloodstream form disrupted autophagy, but did not impede proliferation. Further characterisation showed bloodstream form autophagy mutants retain the capacity to undergo the complex cellular remodelling that occurs during differentiation to the procyclic form and are equally susceptible to dihydroxyacetone-induced cell death as wild type parasites, not supporting a role for autophagy in this cell death mechanism. The RNAi reporter system developed, which also identified TOR1 as a negative regulator controlling YFP-ATG8.2 but not YFP-ATG8.1 autophagosome formation, will enable further targeted analysis of the mechanisms and function of autophagy in the medically relevant bloodstream form of T. brucei

ALMA CO J=6-5 observations of IRAS16293-2422: Shocks and entrainment

Observations of higher-excited transitions of abundant molecules such as CO are important for determining where energy in the form of shocks is fed back into the parental envelope of forming stars. The nearby prototypical and protobinary low-mass hot core, IRAS16293-2422 (I16293) is ideal for such a study. The source was targeted with ALMA for science verification purposes in band 9, which includes CO J=6-5 (E_up/k_B ~ 116 K), at an unprecedented spatial resolution (~0.2", 25 AU). I16293 itself is composed of two sources, A and B, with a projected distance of 5". CO J=6-5 emission is detected throughout the region, particularly in small, arcsecond-sized hotspots, where the outflow interacts with the envelope. The observations only recover a fraction of the emission in the line wings when compared to data from single-dish telescopes, with a higher fraction of emission recovered at higher velocities. The very high angular resolution of these new data reveal that a bow shock from source A coincides, in the plane of the sky, with the position of source B. Source B, on the other hand, does not show current outflow activity. In this region, outflow entrainment takes place over large spatial scales, >~ 100 AU, and in small discrete knots. This unique dataset shows that the combination of a high-temperature tracer (e.g., CO J=6-5) and very high angular resolution observations is crucial for interpreting the structure of the warm inner environment of low-mass protostars.Comment: Accepted for publication in A&A Letter

The RMS Survey: Resolving kinematic distance ambiguities towards a sample of compact HII regions using HI absorption

We present high-resolution HI data obtained using the Australia Telescope Compact Array to resolve the near/far distance ambiguities towards a sample of compact HII regions from the Red MSX Source (RMS) survey. The high resolution data are complemented with lower resolution archival HI data extracted from the Southern and VLA Galactic Plane surveys. We resolve the distance ambiguity for nearly all of the 105 sources where the continuum was strong enough to allow analysis of the HI absorption line structure. This represents another step in the determination of distances to the total RMS sample, which with over 1,000 massive young stellar objects and compact HII regions, is the largest and most complete sample of its kind. The full sample will allow the distribution of massive star formation in the Galaxy to be examined.Comment: Accepted by MNRAS. This paper consists of 15 pages and contains 10 figures and 5 table

SERMeQ Model Produces a Realistic Upper Bound on Calving Retreat for 155 Greenland Outlet Glaciers

The rate of land ice loss due to iceberg calving is a key source of variability among model projections of the 21st century sea level rise. It is especially challenging to account for mass loss due to iceberg calving in Greenland, where ice drains to the ocean through hundreds of outlet glaciers, many smaller than typical model grid scale. Here, we apply a numerically efficient network flowline model (SERMeQ) forced by surface mass balance to simulate an upper bound on decadal calving retreat of 155 grounded outlet glaciers of the Greenland Ice Sheet—resolving five times as many outlets as was previously possible. We show that the upper bound holds for 91% of glaciers examined and that simulated changes in terminus position correlate with observed changes. SERMeQ can provide a physically consistent constraint on forward projections of the dynamic mass loss from the Greenland Ice Sheet associated with different climate projections.Key PointsWe test an upper‐bound model of calving retreat of 155 ocean‐terminating outlet glaciers that drain the Greenland Ice SheetOur physics‐based method produces terminus positions that correlate with observed positions for 103 glaciers without model tuningOur model bounds retreat rates on 91% of glaciers tested, providing a constraint for future sea level projectionsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163401/3/grl61420-sup-0003-2020GL090213-Text_SI-S01.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163401/2/grl61420_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163401/1/grl61420.pd

The RMS Survey: Far-Infrared Photometry of Young Massive Stars

Context: The Red MSX Source (RMS) survey is a multi-wavelength campaign of follow-up observations of a colour-selected sample of candidate massive young stellar objects (MYSOs) in the galactic plane. This survey is returning the largest well-selected sample of MYSOs to date, while identifying other dust contaminant sources with similar mid-infrared colours including a large number of new ultra-compact (UC)HII regions. Aims:To measure the far-infrared (IR) flux, which lies near the peak of the spectral energy distribution (SED) of MYSOs and UCHII regions, so that, together with distance information, the luminosity of these sources can be obtained. Methods:Less than 50% of RMS sources are associated with IRAS point sources with detections at 60 micron and 100 micron, though the vast majority are visible in Spitzer MIPSGAL or IRAS Galaxy Atlas (IGA) images. However, standard aperture photometry is not appropriate for these data due to crowding of sources and strong spatially variable far-IR background emission in the galactic plane. A new technique using a 2-dimensional fit to the background in an annulus around each source is therefore used to obtain far-IR photometry for young RMS sources. Results:Far-IR fluxes are obtained for a total of 1113 RMS candidates identified as young sources. Of these 734 have flux measurements using IGA 60 micron and 100 micron images and 724 using MIPSGAL 70 micron images, with 345 having measurements in both data sets.Comment: 10 pages, 10 figures, 2 Tables, accepted to A&A. A full version of table 1 is available from the lead author or at the CDS upon publicatio

Dose-Dependent Response to Cyclodextrin Infusion in a Rat Model of Verapamil Toxicity

Introduction: Sulfobutylether-b-cyclodextrin (SBE-CD) is a pharmaceutical excipient known to bind verapamil. Following intravenous administration, clearance of SBE-CD approximates glomerular filtration rate. We hypothesized that infusion of SBE-CD would increase time to asystole in a rat model of verapamil toxicity in a dose-dependent manner. The objective was to demonstrate the effect of a range of SBE-CD concentrations in a rat model of verapamil toxicity. Methods: Twenty-five Wistar rats were allocated to control or 1 of 4 intervention groups. All received ketamine and diazepam anesthesia followed by verapamil infusion 32 mg/kg/h. The verapamil infusion for the intervention groups was premixed with SBE-CD in a 1:1, 1:2, 1:4, or 1:8 molar ratio (verapamil to SBE-CD). The control group infusion did not contain SBE-CD. Additional saline or water was added to the infusion so that the total volume infused was the same across groups, and the osmolality was maintained as close to physiologic as possible. Heart rate, respiratory rate, and temperature were monitored. The primary endpoint was time to asystole.Results: Verapamil coinfused with SBE-CD in a molar ratio of 1:4 resulted in prolonged time to asystole compared to control (21.2 minutes vs 17.6 minutes, P , 0.05). There were no differences in time to asystole between control and any other intervention group. There was no significant difference in time to apnea between control and any intervention group. We assessed the effect of a range of SBE-CD concentrations and identified 1 concentration that prolonged time to asystole. Mechanismsthat may explain this effect include optimal volume expansion with a hyperosmolar cyclodextrin containing solution, complexation of verapamil within the hydrophobic cyclodextrin pore, and/or complexation within micelle-like aggregates of cyclodextrin. However, mechanistic explanations for the observed findings are speculative at this point. Conclusion: The 1:4 verapamil to SBE-CD concentration was modestly effective with SBE-CD concentrations above and below this range demonstrating nonstatistically significant improvements in time to asystole. [West J Emerg Med. 2012;13(1):63–67.

Hele-Shaw flow of a nematic liquid crystal

Motivated by the variety of applications in which nematic Hele-Shaw flow occurs, a theoretical model for Hele-Shaw flow of a nematic liquid crystal is formulated and analysed. We derive the thin-film Ericksen-Leslie equations that govern nematic Hele-Shaw flow, and consider two important limiting cases in which we can make significant analytical progress. Firstly, we consider the leading-order problem in the limiting case in which elasticity effects dominate viscous effects, and find that the nematic liquid crystal anchoring on the plates leads to a fixed director field and an anisotropic patterned viscosity that can be used to guide the flow of the nematic. Secondly, we consider the leading-order problem in the opposite limiting case in which viscous effects dominate elasticity effects, and find that the flow is identical to that of an isotropic fluid and the behaviour of the director is determined by the flow. As an example of the insight which can be gained by using the present approach, we then consider the flow of nematic according to a simple model for the squeezing stage of the One Drop Filling method, an important method for the manufacture of Liquid Crystal Displays, in these two limiting cases

VLTI/MIDI 10 micron interferometry of the forming massive star W33A

We report on resolved interferometric observations with VLTI/MIDI of the massive young stellar object (MYSO) W33A. The MIDI observations deliver spectrally dispersed visibilities with values between 0.03 and 0.06, for a baseline of 45m over the wavelength range 8-13 micron. The visibilities indicate that W33A has a FWHM size of approximately 120AU (0.030'') at 8 micron which increases to 240AU at 13 micron, scales previously unexplored among MYSOs. This observed trend is consistent with the temperature falling off with distance. 1D dust radiative transfer models are simultaneously fit to the visibility spectrum, the strong silicate feature and the shape of the mid infrared spectral energy distribution (SED). For any powerlaw density distribution, we find that the sizes (as implied by the visibilities) and the stellar luminosity are incompatible. A reduction to a third of W33A's previously adopted luminosity is required to match the visibilities; such a reduction is consistent with new high resolution 70 micron data from Spitzer's MIPSGAL survey. We obtain best fits for models with shallow dust density distributions of r^(-0.5) and r^(-1.0) and for increased optical depth in the silicate feature produced by decreasing the ISM ratio of graphite to silicates and using optical grain properties by Ossenkopf et al. (1992).Comment: 4 pages, 4 figures. Accepted for ApJ letter