The impact of membrane protein diffusion on GPCR signaling

This research was carried out as part of the Math-+ excellence cluster (DFG EXC 2046, Project A01-11 [HHB, PA]) and was partially funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through the following grants: Project 421152132 SFB1423 subproject C03 (PA), SFB 1470 subproject A01 (PA) and SFB 1114/2 (SW).Spatiotemporal signal shaping in G protein-coupled receptor (GPCR) signaling is now a well-established and accepted notion to explain how signaling specificity can be achieved by a superfamily sharing only a handful of downstream second messengers. Dozens of Gs-coupled GPCR signals ultimately converge on the production of cAMP, a ubiquitous second messenger. This idea is almost always framed in terms of local concentrations, the differences in which are maintained by means of spatial separation. However, given the dynamic nature of the reaction-diffusion processes at hand, the dynamics, in particular the local diffusional properties of the receptors and their cognate G proteins, are also important. By combining some first principle considerations, simulated data, and experimental data of the receptors diffusing on the membranes of living cells, we offer a short perspective on the modulatory role of local membrane diffusion in regulating GPCR-mediated cell signaling. Our analysis points to a diffusion-limited regime where the effective production rate of activated G protein scales linearly with the receptor–G protein complex’s relative diffusion rate and to an interesting role played by the membrane geometry in modulating the efficiency of coupling.Publisher PDFPeer reviewe

The rotation–activity relation of M dwarfs : from K2 to TESS and PLATO

Studies of the rotation–activity relation of late‐type stars are essential to enhance our understanding of stellar dynamos and angular momentum evolution. We study the rotation–activity relation with K2 for M dwarfs, where it is especially poorly understood. We analyzed the light curves of all bright and nearby M dwarfs form the Superblink proper motion catalog that were in the K2 field of view. Using a sample of 430 M dwarfs observed in campaigns C0–C19 in long‐cadence mode, we determined the rotation period and a wealth of activity diagnostics. Our study of the rotation–activity relation based on photometric activity indicators confirmed the previously published abrupt change of the activity level at a rotation period of ∼10 days. Our sample, which is more than three times larger, increases the statistical significance of this finding.PostprintPeer reviewe

Activity and rotation of the X-ray emitting Kepler stars

The relation between magnetic activity and rotation in late-type stars provides fundamental information on stellar dynamos and angular momentum evolution. Rotation/activity studies found in the literature suffer from inhomogeneity in the measure of activity indexes and rotation periods. We overcome this limitation with a study of the X-ray emitting late-type main-sequence stars observed by XMM-Newton and Kepler. We measure rotation periods from photometric variability in Kepler light curves. As activity indicators, we adopt the X-ray luminosity, the number frequency of white-light flares, the amplitude of the rotational photometric modulation, and the standard deviation in the Kepler light curves. The search for X-ray flares in the light curves provided by the EXTraS (Exploring the X-ray Transient and variable Sky) FP-7 project allows us to identify simultaneous X-ray and white-light flares. A careful selection of the X-ray sources in the Kepler field yields 102 main-sequence stars with spectral types from A to M. We find rotation periods for 74 X-ray emitting main-sequence stars, 22 of which without period reported in the previous literature. In the X-ray activity/rotation relation, we see evidence for the traditional distinction of a saturated and a correlated part, the latter presenting a continuous decrease in activity towards slower rotators. For the optical activity indicators the transition is abrupt and located at a period of ~ 10 d but it can be probed only marginally with this sample which is biased towards fast rotators due to the X-ray selection. We observe 7 bona-fide X-ray flares with evidence for a white-light counterpart in simultaneous Kepler data. We derive an X-ray flare frequency of ~ 0.15 d^{-1} , consistent with the optical flare frequency obtained from the much longer Kepler time-series.Comment: Accepted for publication in A&A. 31 pages, 19 figure

Temas y problemas en Antropología Social

El presente texto tiene que ver con el programa de la materia Antropología Cultural y Social dictada en la Facultad de Psicología de nuestra Universidad de La Plata. Sus diversos capítulos cubren varios temas del curso y fueron antecedidos por otros textos temáticos menos formalizados, editados anteriormente por la Cátedra. Nos ha parecido siempre importante adaptar los conocimientos de la Antropología en el marco de las Ciencias Sociales y de la Antropología Social en particular -que constituyen el eje de la materia- con la intención de conformar un eje didáctico de materiales que sean de fácil comprensión y permitan una lectura ulterior de mayor profundidad y continuidad, según el avance en la construcción de los conocimientos por parte de alumnos. Esto es importante por cuanto la disciplina constituye, de acuerdo al nuevo perfil del Plan de Estudios, uno de los cuatro pilares de conocimiento básico de la Psicología. En este sentido, se la considera un ámbito disciplinar académico destacado que aporta a los estudiantes herramientas conceptual-metodológicas básicas para la lectura y comprensión crítica del contexto sociohistórico, cultural y político en el que desarrollan sus prácticas actuales y su futura práctica profesional. Con una perspectiva más amplia se ha pensado, al redactar los capítulos, en el posible interés que puedan tener su lectura en el ámbito general de la Universidad.Facultad de Psicologí

A late Middle Pleistocene Denisovan mandible from the Tibetan Plateau

Denisovans are members of a hominin group who are currently only known directly from fragmentary fossils, the genomes of which have been studied from a single site, Denisova Cave in Siberia. They are also known indirectly from their genetic legacy through gene flow into several low-altitude East Asian populations and high-altitude modern Tibetans6. The lack of morphologically informative Denisovan fossils hinders our ability to connect geographically and temporally dispersed fossil hominins from Asia and to understand in a coherent manner their relation to recent Asian populations. This includes understanding the genetic adaptation of humans to the high-altitude Tibetan Plateau, which was inherited from the Denisovans. Here we report a Denisovan mandible, identified by ancient protein analysis, found on the Tibetan Plateau in Baishiya Karst Cave, Xiahe, Gansu, China. We determine the mandible to be at least 160 thousand years old through U-series dating of an adhering carbonate matrix. The Xiahe specimen provides direct evidence of the Denisovans outside the Altai Mountains and its analysis unique insights into Denisovan mandibular and dental morphology. Our results indicate that archaic hominins occupied the Tibetan Plateau in the Middle Pleistocene epoch and successfully adapted to high-altitude hypoxic environments long before the regional arrival of modern Homo sapiens

Membrane Invaginations Reveal Cortical Sites that Pull on Mitotic Spindles in One-Cell C. elegans Embryos

Asymmetric positioning of the mitotic spindle in C. elegans embryos is mediated by force-generating complexes that are anchored at the plasma membrane and that pull on microtubules growing out from the spindle poles. Although asymmetric distribution of the force generators is thought to underlie asymmetric positioning of the spindle, the number and location of the force generators has not been well defined. In particular, it has not been possible to visualize individual force generating events at the cortex. We discovered that perturbation of the acto-myosin cortex leads to the formation of long membrane invaginations that are pulled from the plasma membrane toward the spindle poles. Several lines of evidence show that the invaginations, which also occur in unperturbed embryos though at lower frequency, are pulled by the same force generators responsible for spindle positioning. Thus, the invaginations serve as a tool to localize the sites of force generation at the cortex and allow us to estimate a lower limit on the number of cortical force generators within the cell

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements