Assimilation of solids during ascent of magmas from the Bartoy Field of the Baikal Region, Siberia

Most investigators ascribe mare basalt magma genesis to partial melting at depths of approximately 130 to greater than 400 km within the cumulate pile deposited from a lunar magma ocean. Mare basalts share with mid-ocean ridge basalts the characteristic of relative depletion in LREE and other incompatible trace elements that arises from melting within 'used' mantle, from which crust-forming elements have already been separated. Some mare basalt types do not show the classical, La-Nd depleted mare basalt REE distributions; however, some types are isotopically heterogeneous. These differences have been ascribed to assimilation, mainly AFC-style, of KREEPy highland material overlying the source region. Might such assimilation occur during magma ascent through the KREEPy material? To gain information from a terrestrial setting on possible assimilation during ascent, we have studied a suite of Quaternary nepheline-hawalites and nepheline-mugearites from the Bartoy cinder cone complex of the Baikal Rift, Siberia. The Bartoy magmas originated from greater than 80 km deep, and erupted through thick Archean crust. We find evidence for assimilation of approximately 31 wt. percent xenocrysts of garnet, aluminous clinopyroxene, kaersutite, and olivine, all presumably from the basalt source region, but no appreciable assimilation of overlying crust, consistent with isotopic constraints. Magmatic superheat made available by rapid ascent and decomposition accounts adequately for the energy of assimilation; no accompanying fractional crystallization is required or evident

Quantifying Effusion Rates at Active Volcanoes through Integrated Time-Lapse Laser Scanning and Photography

During volcanic eruptions, measurements of the rate at which magma is erupted underpin hazard assessments. For eruptions dominated by the effusion of lava, estimates are often made using satellite data; here, in a case study at Mount Etna (Sicily), we make the first measurements based on terrestrial laser scanning (TLS), and we also include explosive products. During the study period (17–21 July, 2012), regular strombolian explosions were occurring within the Bocca Nuova crater, producing a ~50 m high scoria cone and a small lava flow field. TLS surveys over multi-day intervals determined a mean cone growth rate (effusive and explosive products) of ~0.24 m3s-1. Differences between 0.3-m-resolution DEMs acquired at 10-minute intervals captured the evolution of a breakout lava flow lobe advancing at 0.01–0.03 m3s-1. Partial occlusion within the crater prevented similar measurement of the main flow, but integrating TLS data with time-lapse imagery enabled lava viscosity (7.4 × 105 Pa s) to be derived from surface velocities and, hence, a flux of 0.11 m3s-1 to be calculated. The total dense-rock equivalent magma discharge estimates range from ~0.1 to ~0.2 m3s-1 over the measurement period, and suggest that simultaneous estimates from satellite data are somewhat overestimated. Our results support the use of integrated TLS and time-lapse photography for ground-truthing space-based measurements and highlight the value of interactive image analysis when automated approaches such as particle image velocimetry (PIV) fail

Dissociation of Infectivity from Seeding Ability in Prions with Alternate Docking Mechanism

Previous studies identified two mammalian prion protein (PrP) polybasic domains that bind the disease-associated conformer PrPSc, suggesting that these domains of cellular prion protein (PrPC) serve as docking sites for PrPSc during prion propagation. To examine the role of polybasic domains in the context of full-length PrPC, we used prion proteins lacking one or both polybasic domains expressed from Chinese hamster ovary (CHO) cells as substrates in serial protein misfolding cyclic amplification (sPMCA) reactions. After ∼5 rounds of sPMCA, PrPSc molecules lacking the central polybasic domain (ΔC) were formed. Surprisingly, in contrast to wild-type prions, ΔC-PrPSc prions could bind to and induce quantitative conversion of all the polybasic domain mutant substrates into PrPSc molecules. Remarkably, ΔC-PrPSc and other polybasic domain PrPSc molecules displayed diminished or absent biological infectivity relative to wild-type PrPSc, despite their ability to seed sPMCA reactions of normal mouse brain homogenate. Thus, ΔC-PrPSc prions interact with PrPC molecules through a novel interaction mechanism, yielding an expanded substrate range and highly efficient PrPSc propagation. Furthermore, polybasic domain deficient PrPSc molecules provide the first example of dissociation between normal brain homogenate sPMCA seeding ability from biological prion infectivity. These results suggest that the propagation of PrPSc molecules may not depend on a single stereotypic mechanism, but that normal PrPC/PrPSc interaction through polybasic domains may be required to generate prion infectivity

Human Tonsil-Derived Follicular Dendritic-Like Cells are Refractory to Human Prion Infection in Vitro and Traffic Disease-Associated Prion Protein to Lysosomes

The molecular mechanisms involved in human cellular susceptibility to prion infection remain poorly defined. This is due, in part, to the absence of any well characterized and relevant cultured human cells susceptible to infection with human prions, such as those involved in Creutzfeldt-Jakob disease. In variant Creutzfeldt-Jakob disease, prion replication is thought to occur first in the lymphoreticular system and then spread into the brain. We have, therefore, examined the susceptibility of a human tonsil-derived follicular dendritic cell-like cell line (HK) to prion infection. HK cells were found to display a readily detectable, time-dependent increase in cell-associated abnormal prion protein (PrPTSE) when exposed to medium spiked with Creutzfeldt-Jakob disease brain homogenate, resulting in a coarse granular perinuclear PrPTSE staining pattern. Despite their high level of cellular prion protein expression, HK cells failed to support infection, as judged by longer term maintenance of PrPTSE accumulation. Colocalization studies revealed that exposure of HK cells to brain homogenate resulted in increased numbers of detectable lysosomes and that these structures immunostained intensely for PrPTSE after exposure to Creutzfeldt-Jakob disease brain homogenate. Our data suggest that human follicular dendritic-like cells and perhaps other human cell types are able to avoid prion infection by efficient lysosomal degradation of PrPTSE

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)1.

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field

Petrology and geochemistry of stage-I andesites and dacites from the caldera wall of Vol can Colima, Mexico

Se reportan las concentraciones y modos para 10 lavas andesíticas y dacíticas de la Etapa I del Volcán de Colima. Nueve de estas muestras fueron colectadas en la pared de la caldera que se formó por uno o varios eventos tipo colapso Sta. Helena durante el Holoceno. Estos datos se contrastan con los de las lavas emitidas durante Ia Etapa II, que siguió después de la formación de la caldera, y también se discuten en relación con todos los análisis de la cadena Volcán Cántaro, Nevado de Colima y Volcán de Colima cuya edad disminuye de norte a sur. Tanto las lavas de la Etapa I como II del Volcán de Colima muestran cantidades significativamente mayores en Si02 con relación a la escoria producida contemporáneamente durante el Holoceno. Las lavas de la Etapa I muestran valores mayores en Si02 que las lavas de la Etapa II, sin embargo esto también se observa en la evolución del magma del Nevado con el tiempo. Las lavas del Volcán Cántaro están relativamente enriquecida en K20, Sr, La, Ce y Sm comparadas con todas las muestras de la Etapa II del Volcán de Colima, pero cuatro de las lavas de la Etapa I que se discuten en este articulo también muestran estos enriquecimientos. Comparando las lavas de la Etapa II del volcán de Colima con las lavas de la Etapa I y del Volcán Cántaro, muestran valores menores en Yb y Lu y mayores en La/Yb y Sr/Yb. Estas características probablemente reflejan un papel relativamente más importancia del granate residual en las f11entes de los magmas más antiguos, el que podría retener a las tierras raras pesadas. Las lavas del Volcán Cántaro y las de la Etapa I del Volcán de Colima también muestran valores relativamente menores en Rb/Sr que las lavas de Ia Etapa II. Esta diferencia puede rcflejar un cambio en cl tiempo donde disminuye la fuente del manto que contenga anfíbola o cualquier otro mineral que pueda retener Rb cuando se funde. La interpretación preferida para la transición a más altos valores de Yb, Lu y Rb/Sr y más bajos en La/Yb y Sr/Yb después de la formación de la caldera del Volcán de Colima es un cambio en las contribuciones relativas de los componentes de la fuente con una disminución en la fusión de la placa subducida que contiene granate y anfíbola y un incremento en la fusión derivada del mante sobreyaciente. doi: https://doi.org/10.22201/igeof.00167169p.1993.32.4.60