Structure-Function Study of Mammalian Munc18-1 and C. elegans UNC-18 Implicates Domain 3b in the Regulation of Exocytosis

Munc18-1 is an essential synaptic protein functioning during multiple stages of the exocytotic process including vesicle recruitment, docking and fusion. These functions require a number of distinct syntaxin-dependent interactions; however, Munc18-1 also regulates vesicle fusion via syntaxin-independent interactions with other exocytotic proteins. Although the structural regions of the Munc18-1 protein involved in closed-conformation syntaxin binding have been thoroughly examined, regions of the protein involved in other interactions are poorly characterised. To investigate this we performed a random transposon mutagenesis, identifying domain 3b of Munc18-1 as a functionally important region of the protein. Transposon insertion in an exposed loop within this domain specifically disrupted Mint1 binding despite leaving affinity for closed conformation syntaxin and binding to the SNARE complex unaffected. The insertion mutation significantly reduced total amounts of exocytosis as measured by carbon fiber amperometry in chromaffin cells. Introduction of the equivalent mutation in UNC-18 in Caenorhabditis elegans also reduced neurotransmitter release as assessed by aldicarb sensitivity. Correlation between the two experimental methods for recording changes in the number of exocytotic events was verified using a previously identified gain of function Munc18-1 mutation E466K (increased exocytosis in chromaffin cells and aldicarb hypersensitivity of C. elegans). These data implicate a novel role for an exposed loop in domain 3b of Munc18-1 in transducing regulation of vesicle fusion independent of closed-conformation syntaxin binding

Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

Nienow, Sole and Cowton’s Greenland research has been supported by a number of UK NERC research grants (NER/O/S/2003/00620; NE/F021399/1; NE/H024964/1; NE/K015249/1; NE/K014609/1) and Slater has been supported by a NERC PhD studentshipPurpose of the review:  This review discusses the role that meltwater plays within the Greenland ice sheet system. The ice sheet’s hydrology is important because it affects mass balance through its impact on meltwater runoff processes and ice dynamics. The review considers recent advances in our understanding of the storage and routing of water through the supraglacial, englacial, and subglacial components of the system and their implications for the ice sheet Recent findings:   There have been dramatic increases in surface meltwater generation and runoff since the early 1990s, both due to increased air temperatures and decreasing surface albedo. Processes in the subglacial drainage system have similarities to valley glaciers and in a warming climate, the efficiency of meltwater routing to the ice sheet margin is likely to increase. The behaviour of the subglacial drainage system appears to limit the impact of increased surface melt on annual rates of ice motion, in sections of the ice sheet that terminate on land, while the large volumes of meltwater routed subglacially deliver significant volumes of sediment and nutrients to downstream ecosystems. Summary:  Considerable advances have been made recently in our understanding of Greenland ice sheet hydrology and its wider influences. Nevertheless, critical gaps persist both in our understanding of hydrology-dynamics coupling, notably at tidewater glaciers, and in runoff processes which ensure that projecting Greenland’s future mass balance remains challenging.Publisher PDFPeer reviewe

High temporal resolution monitoring of multiple pollutant responses in drainage from an intensively managed grassland catchment caused by a summer storm

This work presents data on a suite of diffuse pollutants, monitored in a stream draining an intensively managed grassland on a 30 min time step during a period of intense rainfall to better understand their sources and pathways. Nitrite (92 mu g l(-1)), particulate phosphorus (107 mu g l(-1)) and soluble phosphorus (74 mu g l(-1)) exceeded environmental limits during base flow. Concentrations of nitrate and nitrite were decreased during the storm event, whereas all other pollutants generally increased and exceeded environmental limits where specified, especially when associated with a small subsidiary hydrograph on the rising limb of the main hydrograph. Total pollutants loads, when using a 60 min sampling frequency, would have led to significant over and under-estimations depending on which 60 min sample set was used. In the worst case, loads of ammonium could have been under-estimated by 35% or over estimated by 25% with errors being associated with loads on the rising limb of the hydrograph and more specifically a small subsidiary hydrograph. This subsidiary hydrograph may have occurred as a result of runoff from the farm hard standings within the catchment. Incidental transfer of pollutants associate with this runoff have masked the overall grassland pollutant response. To better understand these different source areas and pollutant dynamics, there is a need for novel tracing techniques to elucidate their relative contribution and pathways

Stalactite drip-water monitoring and tracer tests approach to assess hydrogeologic behavior of karst vadose zone: case study of Han-sur-Lesse (Belgium)

This paper focuses on the unsaturated zone and epikarst of karst aquifers in order to identify the hydrogeological behavior of these important but poorly understood parts of karst systems. A high-resolution monitoring of stalactite drips and artificial tracer test experiment in the vadose zone allows to draw a conceptual model for the local recharge processes through the unsaturated zone of karst aquifers. Those aquifers represent major groundwater resources in Belgium. Seven years of high-resolution stalactite dripping were recorded on 3 sites of the Han-sur-Lesse cave system (South of Belgium). The three sites show very different discharge variations but a similar behavior from one year to another. Analysis and comparison of the dripping cycles over 7 years highlight the vadose zone behavior and its relationship with surface infiltration (water excess). For each site, a water excess threshold at the beginning of the winter has been identified. This threshold is needed to refill the vadose zone/epikarst capacity before the dripping. The value of the threshold is relatively constant for each site during the 7 years, indicating the regularity of the capacitive system of the vadose zone. Unknown features have also been observed with discharge decrease during high water excess periods, linked to the drainage processes of epikarst. Finally, artificial tracer test reveals the duality of the unsaturated zone behavior, with fast transmissive pathways (velocity of &gt;6 m/h) related to a highly capacitive system (&gt;150 days of tracer restitution).</p

Sediment Budgets in High-Mountain Areas: Review and Challenges

The changes in the sediment transport regimes of high-mountain areas as a consequence of global warming have received growing attention by geomorphologists, not only because these changes can imply a heightened threat to human infrastructure. While many studies dealing with high-mountain sediment transport processes (e.g., rock fall, debris flows, avalanches, stream transport) have focused on one process only, few studies have tried to establish a holistic view of the sediment transport in high-mountain catchments. This review chapter identifies the need for research in high-mountain sediment budgets, aims at providing an overview of studies that have contributed to this goal, and discusses the methodological state of the art in the different steps necessary for sediment budget construction. In addition, relevant research gaps will be identified, thereby showing potential for future research

Functionality of the beta/six site-specific recombination system in tobacco and Arabidopsis: A novel tool for genetic engineering of plant genomes

Gronlund JT, Stemmer C, Lichota J, Merkle T, Grasser KD. Functionality of the beta/six site-specific recombination system in tobacco and Arabidopsis: A novel tool for genetic engineering of plant genomes. Plant Molecular Biology. 2007;63(4):545-556