Using radon to quantify groundwater discharge and methane fluxes to a shallow,tundra lake on the Yukon-Kuskokwim Delta,Alaska

Northern lakes are a source of greenhouse gases to the atmosphere and contribute substantially to the global carbon budget. However, the sources of methane (CH₄) to northern lakes are poorly constrained limiting our ability to the assess impacts of future Arctic change. Here we present measurements of the natural groundwater tracer, radon, and CH₄ in a shallow lake on the Yukon-Kuskokwim Delta, AK and quantify groundwater discharge rates and fluxes of groundwater-derived CH₄. We found that groundwater was significantly enriched (2000%) in radon and CH₄ relative to lake water. Using a mass balance approach, we calculated average groundwater fluxes of 1.2 ± 0.6 and 4.3 ± 2.0 cm day⁻¹, respectively as conservative and upper limit estimates. Groundwater CH₄ fluxes were 7—24 mmol m⁻² day⁻¹ and significantly exceeded diffusive air–water CH₄ fluxes (1.3–2.3 mmol m⁻² day⁻¹) from the lake to the atmosphere, suggesting that groundwater is an important source of CH₄ to Arctic lakes and may drive observed CH₄ emissions. Isotopic signatures of CH₄ were depleted in groundwaters, consistent with microbial production. Higher methane concentrations in groundwater compared to other high latitude lakes were likely the source of the comparatively higher CH₄ diffusive fluxes, as compared to those reported previously in high latitude lakes. These findings indicate that deltaic lakes across warmer permafrost regions may act as important hotspots for CH₄ release across Arctic landscapes.

     

Dependence on different Rab GTPases for the trafficking of CXCR4 and CCR5 homo or heterodimers between the endoplasmic reticulum and plasma membrane in Jurkat cells

Much is known about G protein coupled receptor trafficking and internalization following agonist stimulation. However, much less is known about outward trafficking of receptors from synthesis in the endoplasmic reticulum to the plasma membrane, or the role that trafficking might play in the assembly of receptor signaling complexes, important for targeting, specificity, and rapidity of subsequent signaling events. Up to now, very little is understood about receptor hetero-oligomers other than the fact that their assembly is done rapidly after biosynthesis. In our study we use bimolecular fluorescence complementation to selectively follow receptor dimers when expressed in Jurkat cells in order to clarify the trafficking itinerary those receptors follow to reach the plasma membrane and the resulting effect on signal transduction. CXCR4 and CCR5, previously shown to form both homo and hetero-oligomers, were used as our model to understand the specificities of trafficking along the anterograde pathway. The CXCR4 homodimer relies on Rabs2, 6 and 8 for anterograde transport regardless of the presence of endogenous CD4. The CCR5 homodimer relies on Rabs1 and 11 when CD4 is absent, but Rabs1 and 8 when CD4 was present. Interestingly, similar to the CCR5 homodimer, the CXCR4-CCR5 heterodimer relied on Rabs1 and 11 but also required Rab2 when CD4 was absent, and only Rab 1 when CD4 was present. Our results demonstrate that, although the receptors composing the heterodimeric complex are the same as in the homodimeric ones, the heterodimer traffics and signals differently than each homodimer. Our study demonstrates the importance of considering the receptor heterodimers as distinct signaling entities that should be carefully and individually characterized.     

Conservation of protein phosphorylation sites within gene families and across species

Recent large scale phosphoproteomics studies have helped identify many phosphorylation sites of both membrane and soluble proteins. In most cases the relevance of specific sites has yet to be established whereas in a small number of cases their potency in modulating protein activity is evident. With the increasing amount of data it is becoming clear that phosphosites are often conserved within protein families, pointing to generic regulatory mechanisms. In addition, such mechanisms may be conserved across species. In this addendum evidence is presented for these phenomena occurring in rice and Arabidopsis.Key words: Arabidopsis, kinase, phosphoproteomics, rice     

Potential therapeutic implications of new insights into respiratory syncytial virus disease

Viral bronchiolitis is the most common cause of hospitalization in infants under 6 months of age, and 70% of all cases of bronchiolitis are caused by respiratory syncytial virus (RSV). Early RSV infection is associated with respiratory problems such as asthma and wheezing later in life. RSV infection is usually spread by contaminated secretions and infects the upper then lower respiratory tracts. Infected cells release proinflammatory cytokines and chemokines, including IL-1, tumor necrosis factor-α, IL-6, and IL-8. These activate other cells and recruit inflammatory cells, including macrophages, neutrophils, eosinophils, and T lymphocytes, into the airway wall and surrounding tissues. The pattern of cytokine production by T lymphocytes can be biased toward 'T-helper-1' or 'T-helper-2' cytokines, depending on the local immunologic environment, infection history, and host genetics. T-helper-1 responses are generally efficient in antiviral defense, but young infants have an inherent bias toward T-helper-2 responses. The ideal intervention for RSV infection would be preventive, but the options are currently limited. Vaccines based on protein subunits, live attenuated strains of RSV, DNA vaccines, and synthetic peptides are being developed; passive antibody therapy is at present impractical in otherwise healthy children. Effective vaccines for use in neonates continue to be elusive but simply delaying infection beyond the first 6 months of life might reduce the delayed morbidity associated with infantile disease.     

Bioinformatics: living on the edge

A report on the 11th European Conference on Computational Biology (ECCB), Basel, Switzerland, September 9-12, 2012.