Compositional End Members in Gale Crater, Mars

Geochemical data returned from the Mars Science Laboratory’s Curiosity rover over 1296 sols, has revealed a previously unforeseen martian geochemical complexity. Before Curiosity landed in Gale Crater, Martian SNC meteorite studies along with previous orbiter, rover and lander data showed Mars as being a predominantly basaltic planet with little magmatic differentiation. But through using ChemCam density contour plots to collate compositional data obtained by that instrument, we can identify 4 compositional end members in Gale sedimentary and igneous samples

Foraging Ecology And Habitat Selection Of The Western Yellow Robin (Eopsaltria Griseogularis) In A Wandoo Woodland, Western Australia : Conservation Ecology Of A Declining Species

This study examined the foraging ecology and habitat selection of the Western Yellow Robin in Wandoo Woodland at Dryandra Woodland, Western Australia. The foraging ecology component was comprised of an examination of foraging behaviour, perch-use selection and pounce-site characteristics. The habitat selection component was comprised of an examination of habitat characteristics of site occupancy and general nesting ecology. The implications of current management at Dryandra Woodland to the ecology of the Western Yellow Robin are discussed in reference to the findings of the present study. Ground-pouncing was the dominant foraging behaviour throughout all seasons, with dead branches of live subcanopy Wandoo trees (Eucalyptus wandoo) and dead fallen timber as the dominant perch substrate throughout all seasons. However, interseasonal shifts were detected, exemplified by a decrease in proportion of ground pouncing, and an increase in foraging height and perching height during the warmer months. These results reflect seasonal changes in foraging behaviour influenced by the seasonality of invertebrate prey abundance, with lower abundance of leaf litter invertebrates and increased abundance of flying invertebrates in warmer months. Intraseasonal shifts in foraging behaviour reflect climatic differences between years. Pounce site characteristics showed selection at multiple spatial scales. At the microhabitat scale, pounce sites had significantly more leaf litter and log material, and less bare ground than random points. At the macrohabitat scale, the distance of pounce sites to logs was significantly less than expected. Associations between foraging sites and logs represents selection for sites with a greater abundance of invertebrate prey associated with dead fallen timber. This pattern of selection is consistent throughout the year, indicating characteristics of ground pounce foraging locations remain the same year round regardless of the shift in foraging behaviours. The habitat selection component of the study showed that sites occupied by Western Yellow Robins had higher canopy density, higher leaf litter and log density, higher proportions of Wandoo trees and Gastrolobium plants and higher fragment coefficients (indicating occupation of sites away from the woodland/agricultural ecotone). These results reflect selection of variables at multiple spatial scales; namely, selection for sites with abundant invertebrate prey habitat (microhabitat scale), selection for highly productive habitat (macrohabitat scale), and selection for sites with a reduced edge effect (landscape scale). Nest site characteristics showed selection at specific spatial scales. Although nest sites were located at a variety of heights, they were largely associated with the basal crown height of trees, affording them relatively unobstructed views of the ground to spot potential predators. Nesting trees were similar in height to surrounding trees, although nesting trees were almost always shorter than the highest of the surrounding trees. At a macrohabitat scale, habitat surrounding nest sites was no different to habitat at non-nest sites, indicating no selection for nest site habitat measured. Territory boundaries varied spatially and temporally, with a contraction of territory boundaries during the breeding season. Nests were normally located with the vicinity of the centre of the breeding territory. The present study indicates the strong association of the Western Yellow Robin with the ground environment, with selection for dense leaf litter and logs at numerous spatial scales. The current Dryandra Management Plan strategies have the potential to detrimentally alter the ground environment on which the resource requirements of the Western Yellow Robins revolve. The impact of the proposed changes in land tenure of Dryandra Woodland to National Park would result in additional human pressure on the environment. The impact of an influx in weed invasion, introduction of the Phytophthora dieback fungus and vehicle disturbance by an increase in visitors, has the potential to detrimentally alter the ecology of the habitats occupied by Western Yellow Robins. Furthermore, the implementation of the current fire management plan and the push for tourism development has the potential to internally fragment Dryandra Woodland to the detriment of the Western Yellow Robin. Future research needs to examine reasons for the continued decline in the distribution and abundance of the Western Yellow Robin in the wheatbelt. Such research should be undertaken at the landscape scale, by examining the effects of agricultural practices on the ecology of the species, such as the effect of remnant area, habitat loss, habitat fragmentation and isolation, grazing, weed invasion, altered ecosystem processes and inappropriate fire regimes. Research should also be undertaken on the impact of agricultural practices on the ground invertebrates of remnant native vegetation of the wheatbelt, as many of the above effects of agricultural practices has the potential to greatly disturb the ground environment. Such disturbance has the potential to alter the abundance of ground invertebrates; an important foraging resource of the Western Yellow Robin

Spatial structure and composition of polysaccharide-protein complexes from Small Angle Neutron Scattering

We use Small Angle Neutron Scattering (SANS), with an original analysis method, to obtain both the characteristic sizes and the inner composition of lysozyme-pectin complexes depending on the charge density. Lysozyme is a globular protein and pectin a natural anionic semiflexible polysaccharide with a degree of methylation (DM) 0, 43 and 74. For our experimental conditions (buffer ionic strength I = 2.5 10-2 mol/L and pH between 3 and 7), the electrostatic charge of lysozyme is always positive (from 8 to 17 depending on pH). The pectin charge per elementary chain segment is negative and can be varied from almost zero to one through the change of DM and pH. The weight molar ratio of lysozyme on pectin monomers is kept constant. The ratio of negative charge content per volume to positive charge content per volume, -/+, is varied between 10 and 0.007. On a local scale, for all charged pectins, a correlation peak appears at 0.2 {\AA}-1 due to proteins clustering inside the complexes. On a large scale, the complexes appear as formed of spherical globules with a well defined radius of 10 to 50 nm, containing a few thousands proteins. The volume fraction Phi of organic matter within the globules derived from SANS absolute cross-sections is around 0.1. The protein stacking, which occurs inside the globules, is enhanced when pectin is more charged, due to pH or DM. The linear charge density of the pectin determines the size of the globules for pectin chains of comparable molecular weights whether it is controlled by the pH or the DM. The radius of the globules varies between 10 nm and 50 nm. In conclusion the structure is driven by electrostatic interactions and not by hydrophobic interactions. The molecular weight also has a large influence on the structure of the complexes since long chains tend to form larger globules. This maybe one reason why DM and pH are not completely equivalent in our system since DM 0 has a short mass, but this may not be the only one. For very low pectin charge (-/+ = 0.07), globules do not appear and the scattering signals a gel-like structure. We did not observe any beads-on-a-string structure

Synaptic Vesicle Generation from Activity-Dependent Bulk Endosomes Requires Calcium and Calcineurin

Activity-dependent bulk endocytosis (ADBE) is the dominant mode of synaptic vesicle (SV) endocytosis during high frequency stimulation in central nerve terminals. ADBE generates endosomes direct from the plasma membrane, meaning that high concentrations of calcium will be present in their interior due to fluid phase uptake from the extracellular space. Morphological and fluorescent assays were utilised to track the generation of SVs from bulk endosomes in primary neuronal culture. This process was functionally uncoupled from both SV exocytosis and plasma membrane retrieval events by intervening only after SV fusion and endocytosis were completed. Either intracellular (BAPTA-AM) or intra-endosomal (Rhod-dextran) calcium chelation inhibited SV generation from bulk endosomes, indicating calcium efflux from this compartment is critical for this process. The V-type ATPase antagonist bafilomycin A1 also arrested SV generation from bulk endosomes indicating endosomal acidification may be required for calcium efflux. Finally pharmacological inhibition of the calcium-dependent protein phosphatase calcineurin blocked endosomal SV generation, identifying it as a key downstream effector in this process. These results reveal a novel and key role for the fluid phase uptake of extracellular calcium and its subsequent efflux in the SV lifecycle

Fine-tuning activity-dependent bulk endocytosis via kinases and phosphatases

The regulation of activity-dependent bulk endocytosis, the dominant mode of membrane retrieval in response to intense neuronal activity, is poorly understood. In this JCB issue, Peng et al. (2021. J. Cell. Biol.https://doi.org/10.1083/jcb.202011028) propose a novel molecular mechanism for the coordination of activity-dependent bulk endocytosis that builds on Minibrain kinase and its presynaptic substrate synaptojanin-1.I. Milosevic is supported by funding from the John Black Foundation, John Fell Fund (H5D00100), and Horizon 2020 (MIA-Portugal/857524), while M.A. Cousin is supported by The Wellcome Trust (204954/ Z/16/Z), Simons Foundation (529508), Epilepsy Research UK (P2003), and Cure Huntington’s Disease Initiative (A-11210)

Adaptor Protein Complexes 1 and 3 Are Essential for Generation of Synaptic Vesicles from Activity-Dependent Bulk Endosomes

Activity-dependent bulk endocytosis is the dominant synaptic vesicle retrieval mode during high intensity stimulation in central nerve terminals. A key event in this endocytosis mode is the generation of new vesicles from bulk endosomes, which replenish the reserve vesicle pool. We have identified an essential requirement for both adaptor protein complexes 1 and 3 in this process by employing morphological and optical tracking of bulk endosome-derived synaptic vesicles in rat primary neuronal cultures. We show that brefeldin A inhibits synaptic vesicle generation from bulk endosomes, and that both brefeldin A and shRNA knockdown of either adaptor protein 1 or 3 subunits inhibit reserve pool replenishment from bulk endosomes. Conversely, no plasma membrane function was found for adaptor proteins 1 or 3 in either bulk endosome formation or clathrin-mediated endocytosis. Simultaneous knockdown of both adaptor protein 1 and 3 indicated that they generated the same population of SVs. Thus adaptor protein complex 1 and 3 play an essential dual role in generation of synaptic vesicles during activity-dependent bulk endocytosis

Quantitative Analysis of Synaptic Vesicle Pool Replenishment in Cultured Cerebellar Granule Neurons using FM Dyes

After neurotransmitter release in central nerve terminals, SVs are rapidly retrieved by endocytosis. Retrieved SVs are then refilled with neurotransmitter and rejoin the recycling pool, defined as SVs that are available for exocytosis1,2. The recycling pool can generally be subdivided into two distinct pools - the readily releasable pool (RRP) and the reserve pool (RP). As their names imply, the RRP consists of SVs that are immediately available for fusion while RP SVs are released only during intense stimulation1,2. It is important to have a reliable assay that reports the differential replenishment of these SV pools in order to understand 1) how SVs traffic after different modes of endocytosis (such as clathrin-dependent endocytosis and activity-dependent bulk endocytosis) and 2) the mechanisms controlling the mobilisation of both the RRP and RP in response to different stimuli

Significant techniques in the processing and interpretation of ERTS-1 data

The discipline oriented investigations underway at the Johnson Space Center (JSC) using ERTS-1 data provide an appropriate framework for the systematic evaluation of the various elements comprising a prototype multispectral data processing and analysis system. In particular such a system may be thought of as the integration of: (1) a preprocessing subsystem; (2) a spectral clustering subsystem, (3) a correlation and classification subsystem; (4) mensuration subsystem; and (5) an information management subsystem. Specific elements of this system are already operational at JSC. It is in the context of this system that technique development and application is being pursued at JSC. Aircraft, ERTS and EREP data will be utilized to refine the subsystem elements for each of the data acquisition systems or system combinations that are optimally suited for a specific Earth Resources application. The techniques reported are those that have been developed to date during the utilization of ERTS-1 data in this processing and analysis system

Akt/PKB Controls the Activity-Dependent Bulk Endocytosis of Synaptic Vesicles

Activity-dependent bulk endocytosis (ADBE) is the dominant SV endocytosis mode during intense neuronal activity. The dephosphorylation of Ser774 on dynamin I is essential for triggering of ADBE, as is its subsequent rephosphorylation by glycogen synthase kinase 3 (GSK3). We show that in primary cultures of cerebellar granule neurons the protein kinase Akt phosphorylates GSK3 during intense neuronal activity, ensuring that GSK3 is inactive during intense stimulation to aid dynamin I dephosphorylation. Furthermore, when a constitutively active form of Akt was overexpressed in primary neuronal cultures, ADBE was inhibited with no effect on clathrin-mediated endocytosis. Thus Akt has two major regulatory roles (i) to ensure efficient dynamin I dephosphorylation via acute activity-dependent inhibition of GSK3 and (ii) to negatively regulate ADBE when activated in the longer term. This is the first demonstration of a role for Akt in SV recycling and suggests a key role for this protein kinase in modulating synaptic strength during elevated neuronal activity