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- Morgado, B. E., et al.
(författare)
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A stellar occultation by the transneptunian object (50000) Quaoar observed by CHEOPS
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 664
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Tidskriftsartikel (refereegranskat)abstract
- Context. Stellar occultation is a powerful technique that allows the determination of some physical parameters of the occulting object. The result depends on the photometric accuracy, the temporal resolution, and the number of chords obtained. Space telescopes can achieve high photometric accuracy as they are not affected by atmospheric scintillation. Aims. Using ESA's CHEOPS space telescope, we observed a stellar occultation by the transneptunian object (50000) Quaoar. We compare the obtained chord with previous occultations by this object and determine its astrometry with sub-milliarcsecond precision. Also, we determine upper limits to the presence of a global methane atmosphere on the occulting body. Methods. We predicted and observed a stellar occultation by Quaoar using the CHEOPS space telescope. We measured the occultation light curve from this dataset and determined the dis- and reappearance of the star behind the occulting body. Furthermore, a ground-based telescope in Australia was used to constrain Quaoar's limb. Combined with results from previous works, these measurements allowed us to obtain a precise position of Quaoar at the occultation time. Results. We present the results obtained from the first stellar occultation by a transneptunian object using a space telescope orbiting Earth; it was the occultation by Quaoar observed on 2020 June 11. We used the CHEOPS light curve to obtain a surface pressure upper limit of 85 nbar for the detection of a global methane atmosphere. Also, combining this observation with a ground-based observation, we fitted Quaoar's limb to determine its astrometric position with an uncertainty below 1.0 mas. Conclusions. This observation is the first of its kind, and it shall be considered as a proof of concept of stellar occultation observations of transneptunian objects with space telescopes orbiting Earth. Moreover, it shows significant prospects for the James Webb Space Telescope.
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- Lee, Sarah C., et al.
(författare)
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Nano-encapsulated Escherichia coli Divisome Anchor ZipA, and in Complex with FtsZ
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- The E. coli membrane protein ZipA, binds to the tubulin homologue FtsZ, in the early stage of cell division. We isolated ZipA in a Styrene Maleic Acid lipid particle (SMALP) preserving its position and integrity with native E. coli membrane lipids. Direct binding of ZipA to FtsZ is demonstrated, including FtsZ fibre bundles decorated with ZipA. Using Cryo-Electron Microscopy, small-angle X-ray and neutron scattering, we determine the encapsulated-ZipA structure in isolation, and in complex with FtsZ to a resolution of 1.6 nm. Three regions can be identified from the structure which correspond to, SMALP encapsulated membrane and ZipA transmembrane helix, a separate short compact tether, and ZipA globular head which binds FtsZ. The complex extends 12 nm from the membrane in a compact structure, supported by mesoscale modelling techniques, measuring the movement and stiffness of the regions within ZipA provides molecular scale analysis and visualisation of the early divisome.
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- Liao, Sifang, et al.
(författare)
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Behavioral Senescence and Aging-Related Changes in Motor Neurons and Brain Neuromodulator Levels Are Ameliorated by Lifespan-Extending Reproductive Dormancy in Drosophila
- 2017
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Ingår i: Frontiers in Cellular Neuroscience. - : Frontiers Media SA. - 1662-5102. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- The lifespan of Drosophila melanogaster can be extended substantially by inducing reproductive dormancy (also known as diapause) by lowered temperature and short days. This increase of longevity is accompanied by lowered metabolism and increased stress tolerance. We ask here whether behavioral senescence is ameliorated during adult dormancy. To study this we kept flies for seven or more weeks in normal rearing conditions or in diapause conditions and compared to 1-week-old flies in different behavioral assays of sleep, negative geotaxis and exploratory walking. We found that the senescence of geotaxis and locomotor behavior seen under normal rearing conditions was negligible in flies kept in dormancy. The normal senescence of rhythmic activity and sleep patterns during the daytime was also reduced by adult dormancy. Investigating the morphology of specific neuromuscular junctions (NMJs), we found that changes normally seen with aging do not take place in dormant flies. To monitor age-associated changes in neuronal circuits regulating activity rhythms, sleep and walking behavior we applied antisera to tyrosine hydroxylase (TH), serotonin and several neuropeptides to examine changes in expression levels and neuron morphology. In most neuron types the levels of stored neuromodulators decreased during normal aging, but not in diapause treated flies. No signs of neurodegeneration were seen in either condition. Our data suggest that age-related changes in motor neurons could be the cause of part of the behavioral senescence and that this is ameliorated by reproductive diapause. Earlier studies established a link between age-associated decreases in neuromodulator levels and behavioral decline that could be rescued by overexpression of neuromodulator. Thus, it is likely that the retained levels of neuromodulators in dormant flies alleviate behavioral senescence.
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- Söderberg, Jeannette, 1983-
(författare)
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Neuropeptides and GABA in control of insulin producing cells in Drosophila
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Insulin plays an important role in metabolic regulation as well as in growth, fecundity and stress resistance. In order to understand more about the regulation of insulin-like peptide (DILP) production and release we investigate the impact of neuropeptide (DTK) signaling and classical neurotransmitter (GABA) signaling onto the insulin producing cells of the Drosophila brain. DTK was shown to regulate insulin production through DTK receptors found on the insulin producing cells of the brain. DTK has an impact on carbohydrate and lipid levels as well as effect stress resistance (Paper I). Manipulations of DTK signaling differentially affect Dilp transcript levels. We also showed that GABA regulates the production and release of insulin-like peptides via GABABRs (Paper II). Both these two signaling pathways have an inhibitory action on insulin production and release. The Malpighian (renal) tubules were discovered as a novel site of insulin-like peptide expression and DTK signaling was shown to converge on the insulin pathway also here (Paper III). Stress seems to induce hormonal release of DTK that acts on the renal tubules to regulate DILP 5 signaling. Manipulations of superoxide dismutase (SOD2) in principal cells also affect survival at stress, suggesting that DILP 5 acts locally on tubules, possibly in oxidative stress regulation. Finally, we demonstrated that a cholecystokinin-like (CCK) peptide, DSK, is present in the IPCs and affects meal size regulation and food preference (Paper IV). DSK, like CCK, therefore acts to induce satiety. DSK and Dilp transcripts levels were also found to affect each other, suggesting coordination and possibly a feedback mechanism between the two signaling pathways. In summary, we have studied control of Insulin signaling in Drosophila and have found that the different DILP isoforms have may separate functions and that they are separately regulated by both neuropeptides and classical neurotransmitters.
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