Lipid Clustering Correlates with Membrane Curvature as Revealed by Molecular Simulations of Complex Lipid Bilayers

Cell membranes are complex multicomponent systems, which are highly heterogeneous in the lipid distribution and composition. To date, most molecular simulations have focussed on relatively simple lipid compositions, helping to inform our understanding of in vitro experimental studies. Here we describe on simulations of complex asymmetric plasma membrane model, which contains seven different lipids species including the glycolipid GM3 in the outer leaflet and the anionic lipid, phosphatidylinositol 4,5-bisphophate (PIP₂), in the inner leaflet. Plasma membrane models consisting of 1500 lipids and resembling the in vivo composition were constructed and simulations were run for 5 µs. In these simulations the most striking feature was the formation of nano-clusters of GM3 within the outer leaflet. In simulations of protein interactions within a plasma membrane model, GM3, PIP₂, and cholesterol all formed favorable interactions with the model α-helical protein. A larger scale simulation of a model plasma membrane containing 6000 lipid molecules revealed correlations between curvature of the bilayer surface and clustering of lipid molecules. In particular, the concave (when viewed from the extracellular side) regions of the bilayer surface were locally enriched in GM3. In summary, these simulations explore the nanoscale dynamics of model bilayers which mimic the in vivo lipid composition of mammalian plasma membranes, revealing emergent nanoscale membrane organization which may be coupled both to fluctuations in local membrane geometry and to interactions with proteins.     

Seasonal acquisition of mineral nutrients by a chalcid gall on lowbush blueberry

Seasonal accumulation of various mineral nutrients by galls of the chalcidHemadas nubilipennis on lowbush blueberry were examined in various phases of gall development. Levels of copper, nickel iron and zinc were higher in tissues of galls in initiation phase compared to tips of ungalled shoots and in general were higher than galls in growth and maturation phases. Levels of manganese and magnesium in gall tissues decrease throughout the season compared to ungalled shoots. Levels of calcium are less in gall tissue in initiation phase compared to ungalled shoots, and elevated in maturation phase. Patterns of mineral concentration within galls at various phases of development are related to known physiological roles of minerals in plant nutrition; however we conclude that patterns are variable and their significance in gall physiology requires further study.     

Fine needle aspiration of palpable breast lesions. Results obtained with cytocentrifuge preparation of aspirates

The use of cytocentrifugation in the preparation of fine needle aspiration (FNA) specimens from the breast was evaluated. A total of 174 fine needle aspirates of breast masses were flushed into cytospin Collection Fluid, from which Papanicolaou-stained Cytospin preparations were made in the laboratory. Comparison of these preparations to conventional smears of aspirates showed no significant differences in the number or morphology of the cells. In 148 cases, the FNA cytologic study was followed up by excisional biopsy, Tru-Cut biopsy and/or a combination of mammography and clinical follow-up of two to nine months. Of 36 verified carcinomas, 31 (86%) were correctly diagnosed, with a zero false-positive rate. Among the 74 cytologically benign aspirates, 2 carcinomas were found on open biopsy, giving a false-negative rate of 3%. Lipomas were not diagnosable with this technique. This technique should be considered in institutions with a high turnover of junior staff members, which frequently results in a higher number of poorly smeared specimens or in poorly fixed/air-dried specimens that give suboptimal results with the Papanicolaou stain. With this method, there is less risk of creation of potentially hazardous aerosols and further preparations for additional studies may be made if required.