Theory of Raft Formation by the Cross-Linking of Saturated or Unsaturated Lipids in Model Lipid Bilayers

AbstractWe consider the effect of cross-linking a small fraction of lipids, either saturated or unsaturated, in a mixture of saturated and unsaturated lipids and cholesterol. The change in phase behavior is examined utilizing a recent phenomenological model of the ternary system, which is extended to include a fourth component representing the cross-linked lipids. These lipids are taken to be identical to monomeric ones except for their reduced entropy of mixing. We find that even a relatively small amount of cross-linked lipids, less than 5 mol %, is sufficient to significantly expand the range of compositions within which there is coexistence between liquid-ordered and liquid-disordered phases. Equivalently, the cross-linking of lipids increases the liquid-liquid miscibility transition temperature, and therefore could bring about phase separation at a temperature at which, before cross-linking, there was only a single liquid phase

Phenomenological Model and Phase Behavior of Saturated and Unsaturated Lipids and Cholesterol

We present a phenomenological theory for the phase behavior of ternary mixtures of cholesterol and saturated and unsaturated lipids, one which describes both liquid and gel phases, and illuminates the mechanism of the behavior. In a binary system of the lipids, the two phase separate when the saturated chains are well ordered, as in the gel phase, simply due to packing effects. In the liquid phase the saturated ones are not sufficiently well ordered for separation to occur. The addition of cholesterol, however, increases the saturated lipid order to the point that phase separation is once again favorable. For the system above the main chain transition of the saturated lipid, we can obtain phase diagrams in which there is liquid-liquid phase separation in the ternary system but not in any of the binary ones, while below that temperature we obtain the more common phase diagram in which a gel phase, rich in saturated lipid, appears in addition to the two liquid phases.Comment: 16 pages, 2 figure

Coarsening Dynamics of Domains in Lipid Membranes

We investigate isothermal diffusion and growth of micron-scale liquid domains within membranes of free-floating giant unilamellar vesicles with diameters between 80 and 250 Am. Domains appear after a rapid temperature quench, when the membrane is cooled through a miscibility phase transition such that coexisting liquid phases form. In membranes quenched far from a miscibility critical point, circular domains nucleate and then progress within seconds to late stage coarsening in which domains grow via two mechanisms 1), collision and coalescence of liquid domains, and 2), Ostwald ripening. Both mechanisms are expected to yield the same growth exponent, alpha = 1/3, where domain radius grows as time(alpha). We measure alpha = 0.28 +/- 0.05, in excellent agreement. In membranes close to a miscibility critical point, the two liquid phases in the membrane are bicontinuous. A quench near the critical composition results in rapid changes in morphology of elongated domains. In this case, we measure alpha = 0.50 +/- 0.16, consistent with theory and simulation

Anti-microbial Functions of group 3 innate lymphoid cells in gut-associated lymphoid tissues are regulated by G-protein-coupled receptor 183

Summary: The intestinal tract is constantly exposed to various stimuli. Group 3 innate lymphoid cells (ILC3s) reside in lymphoid organs and in the intestinal tract and are required for immunity to enteric bacterial infection. However, the mechanisms that regulate the ILC3s in vivo remain incompletely defined. Here, we show that GPR183, a chemotactic receptor expressed on murine and human ILC3s, regulates ILC3 migration toward its ligand 7α,25-dihydroxycholesterol (7α,25-OHC) in vitro, and GPR183 deficiency in vivo leads to a disorganized distribution of ILC3s in mesenteric lymph nodes and decreased ILC3 accumulation in the intestine. GPR183 functions intrinsically in ILC3s, and GPR183-deficient mice are more susceptible to enteric bacterial infection. Together, these results reveal a role for the GPR183-7α,25-OHC pathway in regulating the accumulation, distribution, and anti-microbial and tissue-protective functions of ILC3s and define a critical role for this pathway in promoting innate immunity to enteric bacterial infection. : Chu et al. demonstrate that GPR183 and its ligand 7α,25-OHC regulate the accumulation, distribution, and anti-microbial and tissue-protective functions of group 3 innate lymphoid cells, thus revealing a critical role for this pathway in promoting innate immunity against enteric bacterial infection. Keywords: group 3 innate lymphoid cells, GPR183, mesenteric lymph node, intestine, accumulation, distribution, anti-microbia

Social capital, social inclusion and changing school contexts: a Scottish perspective

This paper synthesises a collaborative review of social capital theory, with particular regard for its relevance to the changing educational landscape within Scotland. The review considers the common and distinctive elements of social capital, developed by the founding fathers – Putnam, Bourdieu and Coleman – and explores how these might help to understand the changing contexts and pursue opportunities for growth

Mediated Diasporas: Material Translations of the Philippines in a Globalized World

Recent work demonstrates the ways that new media and ICTs both in the Philippines and among Filipino diasporans have become central to contemporary processes of identity formation, altering and enabling the articulation of alternative selves and expanding spatially Filipino national identifications and definitions of ‘home’ (Pertierra 2002, 2006, 2010 Tyner and Kuhlke 2000, Ignacio 2005). While attending to media in the specific sense of particular social technologies of mass communication, we extend that work here drawing together new empirical studies both to demonstrate the various ways that a wide range of differently situated migrants make use of those media and by considering processes of mediation in a much broader sense (Mazzarella 2004), an approach that draws together both an analysis of the ‘materialities of migration’ (Basu and Coleman 2008) and ‘the technics of translation’ (Rafael 2005)

Gut Microbiome Dysbiosis in Antibiotic-Treated COVID-19 Patients is Associated with Microbial Translocation and Bacteremia

Although microbial populations in the gut microbiome are associated with COVID-19 severity, a causal impact on patient health has not been established. Here we provide evidence that gut microbiome dysbiosis is associated with translocation of bacteria into the blood during COVID-19, causing life-threatening secondary infections. We first demonstrate SARS-CoV-2 infection induces gut microbiome dysbiosis in mice, which correlated with alterations to Paneth cells and goblet cells, and markers of barrier permeability. Samples collected from 96 COVID-19 patients at two different clinical sites also revealed substantial gut microbiome dysbiosis, including blooms of opportunistic pathogenic bacterial genera known to include antimicrobial-resistant species. Analysis of blood culture results testing for secondary microbial bloodstream infections with paired microbiome data indicates that bacteria may translocate from the gut into the systemic circulation of COVID-19 patients. These results are consistent with a direct role for gut microbiome dysbiosis in enabling dangerous secondary infections during COVID-19

An Integrated Framework for Intersectorality: Nonprofitness and Its Influence on Society and Public Administration Programs

Cross-sector interactions have long occurred in the public delivery of goods, services, and interests. While scholars have often addressed cross-sector interactions using the dimensions of publicness (state) and privateness (market), an intersectoral framework necessitates the understanding and incorporation of nonprofitness to account for the dimensions of nonprofits along the public-private continuum. This article proposes a framework for identifying the dimensions of nonprofits in an intersectoral world and draws on relevant examples to illustrate the presence and influence of nonprofitness. The article then focuses on the future of education in the field of public administration and, in light of the proposed framework, makes and considers recommendations to help educational programs better equip students to appreciate work across sectors

Civil society and the state in Uganda’s AIDS response

This paper investigates state-civil society relations in the Ugandan AIDS response through a critical exploration of the history of Uganda’s ‘multi-sectoral’ and ‘partnership’ approaches, particularly as it pertains to The AIDS Support Organisation (TASO). It finds that the Ugandan government’s reputation for successful prevention campaigns is not necessarily deserved, and that the effectiveness of civil society is limited by an authoritarian political culture. Despite these limitations, however, state-civil society partnership did contribute to the emergence of a relatively effective coalition for action against HIV/AIDS. Donors were essential in encouraging the emergence of this coalition, but have also inadvertently undermined the emergence of strong and independent civil society voices able to hold the Ugandan state accountable

Phase Behavior of a Model Bilayer Membrane with Coupled Leaves☆

We discuss the thermodynamic behavior of a bilayer composed of two coupled leaves and derive the Gibbs Phase Rule for such a system. A simple phenomenological model of such a system is considered in which the state of the bilayer is specified by the relative number of ordering lipids in the outer leaf, and in the inner leaf. Two cases are treated. In the first, both inner and outer leaves could undergo phase separation when uncoupled from one another. The bilayer can exist in four different phases, and can exhibit three-phase coexistence. In the second case, an outer layer which can undergo phase separation by itself is coupled to an inner leaf which cannot. We find that when the coupling is weak, the bilayer can exist in only two phases, one in which the outer layer is rich in ordering lipids and the inner leaf is somewhat richer in them than when uncoupled, and another in which the outer layer is poor in ordering lipids and the inner leaf is poorer in them than when uncoupled. Increasing the coupling increases the effect on the inner leaf composition due to small changes in those of the outer leaf. For sufficiently large coupling, a phase transition occurs and the bilayer exhibits four phases as in the first case considered. Our results are in accord with several observations made recently