Liquid-vapor oscillations of water in hydrophobic nanopores

Water plays a key role in biological membrane transport. In ion channels and water-conducting pores (aquaporins), one dimensional confinement in conjunction with strong surface effects changes the physical behavior of water. In molecular dynamics simulations of water in short (0.8 nm) hydrophobic pores the water density in the pore fluctuates on a nanosecond time scale. In long simulations (460 ns in total) at pore radii ranging from 0.35 nm to 1.0 nm we quantify the kinetics of oscillations between a liquid-filled and a vapor-filled pore. This behavior can be explained as capillary evaporation alternating with capillary condensation, driven by pressure fluctuations in the water outside the pore. The free energy difference between the two states depends linearly on the radius. The free energy landscape shows how a metastable liquid state gradually develops with increasing radius. For radii larger than ca. 0.55 nm it becomes the globally stable state and the vapor state vanishes. One dimensional confinement affects the dynamic behavior of the water molecules and increases the self diffusion by a factor of two to three compared to bulk water. Permeabilities for the narrow pores are of the same order of magnitude as for biological water pores. Water flow is not continuous but occurs in bursts. Our results suggest that simulations aimed at collective phenomena such as hydrophobic effects may require simulation times longer than 50 ns. For water in confined geometries, it is not possible to extrapolate from bulk or short time behavior to longer time scales.Comment: 20 pages, 4 figures, 3 tables; to be published in Proc. Natl. Acad. Sci. US

A YY1-dependent increase in aerobic metabolism is indispensable for intestinal organogenesis

During late gestation, villi extend into the intestinal lumen to dramatically increase the surface area of the intestinal epithelium, preparing the gut for the neonatal diet. Incomplete development of the intestine is the most common gastrointestinal complication in neonates, but the causes are unclear. We provide evidence in mice that Yin Yang 1 (Yy1) is crucial for intestinal villus development. YY1 loss in the developing endoderm had no apparent consequences until late gestation, after which the intestine differentiated poorly and exhibited severely stunted villi. Transcriptome analysis revealed that YY1 is required for mitochondrial gene expression, and ultrastructural analysis confirmed compromised mitochondrial integrity in the mutant intestine. We found increased oxidative phosphorylation gene expression at the onset of villus elongation, suggesting that aerobic respiration might function as a regulator of villus growth. Mitochondrial inhibitors blocked villus growth in a fashion similar to Yy1 loss, thus further linking oxidative phosphorylation with late-gestation intestinal development. Interestingly, we find that necrotizing enterocolitis patients also exhibit decreased expression of oxidative phosphorylation genes. Our study highlights the still unappreciated role of metabolic regulation during organogenesis, and suggests that it might contribute to neonatal gastrointestinal disorders

Towards sustainable urban water services in developing countries: Tariffs based on willingness-to-pay studies

Water supply and sanitation (WASH) service providers in most towns of developing countries, such as Godey Town in Ethiopia, the case study reported in this paper, deliver less than basic services. The costs for meeting the more ambitious WASH targets of the Sustainable Development Goals will be much higher than what has previously been invested in the sector. This study showed that a tariff structure designed using affordability and willingness-to-pay data would provide higher revenues than one solely based on estimated customers’ affordability, or Ethiopian government’s tariff guidelines. As in previous studies in Ethiopia, this study highlights government’s low willingness-to-charge amidst a high customers’ willingness-to-pay. Yet, there is need to increase water tariffs in developing countries, hence, moving towards financial sustainability and supplementing the other two Ts - taxes and transfers. Based on accurate and updated socio-economic data, the tariff can also be optimised to fulfil the social equity objective

Systems biologists seek fuller integration of systems biology approaches in new cancer research programs

Systems biology takes an interdisciplinary approach to the systematic study of complex interactions in biological systems. This approach seeks to decipher the emergent behaviors of complex systems rather than focusing only on their constituent properties. As an increasing number of examples illustrate the value of systems biology approaches to understand the initiation, progression, and treatment of cancer, systems biologists from across Europe and the United States hope for changes in the way their field is currently perceived among cancer researchers. In a recent EU-US workshop, supported by the European Commission, the German Federal Ministry for Education and Research, and the National Cancer Institute of the NIH, the participants discussed the strengths, weaknesses, hurdles, and opportunities in cancer systems biology

Acute WNT signalling activation perturbs differentiation within the adult stomach and rapidly leads to tumour formation

A role for WNT signalling in gastric carcinogenesis has been suggested due to two major observations. First, patients with germline mutations in adenomatous polyposis coli (APC) are susceptible to stomach polyps and second, in gastric cancer, WNT activation confers a poor prognosis. However, the functional significance of deregulated WNT signalling in gastric homoeostasis and cancer is still unclear. In this study we have addressed this by investigating the immediate effects of WNT signalling activation within the stomach epithelium. We have specifically activated the WNT signalling pathway within the mouse adult gastric epithelium via deletion of either glycogen synthase kinase 3 (GSK3) or APC or via expression of a constitutively active β-catenin protein. WNT pathway deregulation dramatically affects stomach homoeostasis at very short latencies. In the corpus, there is rapid loss of parietal cells with fundic gland polyp (FGP) formation and adenomatous change, which are similar to those observed in familial adenomatous polyposis. In the antrum, adenomas occur from 4 days post-WNT activation. Taken together, these data show a pivotal role for WNT signalling in gastric homoeostasis, FGP formation and adenomagenesis. Loss of the parietal cell population and corresponding FGP formation, an early event in gastric carcinogenesis, as well as antral adenoma formation are immediate effects of nuclear β-catenin translocation and WNT target gene expression. Furthermore, our inducible murine model will permit a better understanding of the molecular changes required to drive tumourigenesis in the stomach

A Hydrophobic Gate in an Ion Channel: The Closed State of the Nicotinic Acetylcholine Receptor

The nicotinic acetylcholine receptor (nAChR) is the prototypic member of the `Cys-loop' superfamily of ligand-gated ion channels which mediate synaptic neurotransmission, and whose other members include receptors for glycine, gamma-aminobutyric acid, and serotonin. Cryo-electron microscopy has yielded a three dimensional structure of the nAChR in its closed state. However, the exact nature and location of the channel gate remains uncertain. Although the transmembrane pore is constricted close to its center, it is not completely occluded. Rather, the pore has a central hydrophobic zone of radius about 3 A. Model calculations suggest that such a constriction may form a hydrophobic gate, preventing movement of ions through a channel. We present a detailed and quantitative simulation study of the hydrophobic gating model of the nicotinic receptor, in order to fully evaluate this hypothesis. We demonstrate that the hydrophobic constriction of the nAChR pore indeed forms a closed gate. Potential of mean force (PMF) calculations reveal that the constriction presents a barrier of height ca. 10 kT to the permeation of sodium ions, placing an upper bound on the closed channel conductance of 0.3 pS. Thus, a 3 A radius hydrophobic pore can form a functional barrier to the permeation of a 1 A radius Na+ ion. Using a united atom force field for the protein instead of an all atom one retains the qualitative features but results in differing conductances, showing that the PMF is sensitive to the detailed molecular interactions.Comment: Accepted by Physical Biology; includes a supplement and a supplementary mpeg movie can be found at http://sbcb.bioch.ox.ac.uk/oliver/download/Movies/watergate.mp

Wnt signaling is boosted during intestinal regeneration by a CD44-positive feedback loop

Enhancement of Wnt signaling is fundamental for stem cell function during intestinal regeneration. Molecular modules control Wnt activity by regulating signal transduction. CD44 is such a positive regulator and a Wnt target gene. While highly expressed in intestinal crypts and used as a stem cell marker, its role during intestinal homeostasis and regeneration remains unknown. Here we propose a CD44 positive-feedback loop that boosts Wnt signal transduction, thus impacting intestinal regeneration. Excision of Cd44 in Cd44$^{fl/fl}$;VillinCreER$^{T2}$ mice reduced Wnt target gene expression in intestinal crypts and affected stem cell functionality in organoids. Although the integrity of the intestinal epithelium was conserved in mice lacking CD44, they were hypersensitive to dextran sulfate sodium, and showed more severe inflammation and delayed regeneration. We localized the molecular function of CD44 at the Wnt signalosome, and identified novel DVL/CD44 and AXIN/CD44 complexes. CD44 thus promotes optimal Wnt signaling during intestinal regeneration

Uptake of home-based voluntary HIV testing in sub-Saharan Africa: a systematic review and meta-analysis

Improving access to HIV testing is a key priority in scaling up HIV treatment and prevention services. Home-based voluntary counselling and testing (HBT) as an approach to delivering wide-scale HIV testing is explored here

CRISPR activation screen in mice identifies novel membrane proteins enhancing pulmonary metastatic colonisation

Abstract Melanoma represents ~5% of all cutaneous malignancies, yet accounts for the majority of skin cancer deaths due to its propensity to metastasise. To develop new therapies, novel target molecules must to be identified and the accessibility of cell surface proteins makes them attractive targets. Using CRISPR activation technology, we screened a library of guide RNAs targeting membrane protein-encoding genes to identify cell surface molecules whose upregulation enhances the metastatic pulmonary colonisation capabilities of tumour cells in vivo. We show that upregulated expression of the cell surface protein LRRN4CL led to increased pulmonary metastases in mice. Critically, LRRN4CL expression was elevated in melanoma patient samples, with high expression levels correlating with decreased survival. Collectively, our findings uncover an unappreciated role for LRRN4CL in the outcome of melanoma patients and identifies a potential therapeutic target and biomarker.info:eu-repo/semantics/publishe