פרסומים

During cellular migration, regulated actin assembly takes place at the cell leading edge, with continuous disassembly deeper in the cell interior. Actin polymerization at the plasma membrane results in the extension of cellular protrusions in the form of lamellipodia and filopodia. To understand how cells regulate the transformation of lamellipodia into filopodia, and to determine the major factors that control their transition, we studied actin self-assembly in the presence of Arp2/3 complex, WASp-VCA and fascin, the major proteins participating in the assembly of lamellipodia and filopodia. We show that in the early stages of actin polymerization fascin is passive while Arp2/3 mediates the formation of dense and highly branched aster-like networks of actin. Once filaments in the periphery of an aster get long enough, fascin becomes active, linking the filaments into bundles which emanate radially from the aster’s surface, resulting in the formation of star-like structures. We show that the number of bundles nucleated per star, as well as their thickness and length, is controlled by the initial concentration of Arp2/3 complex ([Arp2/3]). Specifically, we tested several values of [Arp2/3] and found that for given initial concentrations of actin and fascin, the number of bundles per star, as well as their length and thickness are larger when [Arp2/3] is lower. Our experimental findings can be interpreted and explained using a theoretical scheme which combines Kinetic Monte Carlo simulations for aster growth, with a simple mechanistic model for bundles’ formation and growth. According to this model, bundles emerge from the aster’s (sparsely branched) surface layer. Bundles begin to form when the bending energy associated with bringing two filaments into contact is compensated by the energetic gain resulting from their fascin linking energy. As time evolves the initially thin and short bundles elongate, thus reducing their bending energy and allowing them to further associate and create thicker bundles, until all actin monomers are consumed. This process is essentially irreversible on the time scale of actin polymerization. Two structural parameters, L, which is proportional to the length of filament tips at the aster periphery and b, the spacing between their origins, dictate the onset of bundling; both depending on [Arp2/3]. Cells may use a similar mechanism to regulate filopodia formation along the cell leading edge. Such a mechanism may allow cells to have control over the localization of filopodia by recruiting specific proteins that regulate filaments length (e. g., Dia2) to specific sites along lamellipodia.

Beyond the walls of their synagogues, Jewish adults are creating religious meaning in new and diverse ways in a range of unconventional sites. In Back to School, authors Alex Pomson and Randal F. Schnoor argue that the Jewish day school serves as one such site by bringing adults and children together for education, meeting, study, and worship-like ceremonies. Pomson and Schnoor suggest that day school functions as a locus of Jewish identity akin to the Jewish streets or neighborhoods that existed in many major North American cities in the first half of the twentieth century.

Back to School began as an ethnographic study of the Paul Penna Downtown Jewish Day School (DJDS) in Toronto, a private, religiously pluralistic day school that balances its Jewish curriculum with general studies. Drawing on a longitudinal study at DJDS, and against the backdrop of a comparative study of two other Toronto day schools as well as four day schools from the U.S. Midwest, Pomson and Schnoor argue that when parents choose Jewish schools for their children they look for institutions that satisfy not only their children's academic and emotional needs but also their own social and personal concerns as Jewish adults. The authors found an uncommon degree of involvement and engagement on the part of the parents, as genuine friendships and camaraderie blossomed between parents, faculty, and administrators. In addition, the authors discovered that parents who considered themselves secular Jews were introduced to or reacquainted with the depth and meaning of Jewish tradition and rituals through observing or taking part in school activities.

Sitting on the cusp between the disciplines of education and the sociology of contemporary Jewish life, Back to School offers important policy implications for how Jewish day schools might begin to re-imagine their relationships with parents. Jewish parents, Jewish studies scholars, as well as researchers of educational and social trends will enjoy this evocative volume.

The actual mechanism of cholesterol reduction by phytosterols is yet to be explored. One hypothesis states that cholesterol and phytosterols compete on the solubilization locus within gastric bile salt micelles. In this study competitive solubilization within microemulsions as vehicles for dietary intake of cholesterol and phytosterols was studied by pulse gradient spin-echo nuclear magnetic resonance. The loaded microemulsions undergo phase transitions as a function of dilution, the type of solubilized sterol, and the weight ratio of the cosolubilized sterols. Microemulsions containing 10-20 wt% of aqueous phase, show similar diffusivity of the oil and aqueous phases in all examined systems (excluding PS-loaded one) reflecting the minor influence of these solubilizates on the structure of the inner and the outer phases. The closeness of these structures enables the mobility of water molecules between them. Upon further dilution (> 20 wt% aqueous phase), significant differences in decrease rate of the oil and increase of the water phases mobilities (occurring upon inversion), were detected within the studied systems. It was concluded that the solubilized sterols influence the structural transitions based on their location within the structures and their competitive solubilization. The phytosterols solubilized mostly in the continuous oil phase and between the surfactant tails. Cholesterol is solubilized in the vicinity of the surfactant headgroups and affects the surface curvature. In mixtures of cholesterol and phytosterols, structural changes are dictated mostly by the presence of the cholesterol. (c) 2008 Elsevier Inc. All rights reserved.

Crystallization of carbarnazepine (CBZ), an antiepileptic drug, precipitated from confined spaces of nonionic microemulsions was investigated. The study was aimed to correlate the structure of the microemulsion [water-in-oil (W/O), bicontinuous, and oil-in-water (OIW)] with the crystalline structure and morphology of solid CBZ. The precipitated CBZ was studied by DSC, TGA, powder XRD, single-crystal XRD, SEM, and optical microscopy. The results suggest that the microstructure of the microemulsions influences the crystallization process and allows crystallizing polymorphs that exhibit different crystal structure and habits. W/O nanodroplets orient the crystallizing CBZ molecules to form a prismlike anhydrous polymorphic form with monoclinic unit cell and P2(1)/n space group. Bicontinuous structures lead to platelike dihydrate crystals with orthorhombic unit cell and Cmca space group. The O/W nanodroplets cause the formation of needlelike dihydrate crystals with monoclinic unit cell and P2(1)/c space group. The morphological features of solid CBZ remain predetermined by the basic symmetry and parameters of its unit cell. Precipitation of CBZ pseudopolymorphs from supersaturated microemulsion is discussed in terms of oriented attachment that provides perfect packing of numerous separately nucleated ordered nuclei of CBZ into microscale platelets and then into macroscopic crystals. Crystallization from microemulsion media enabling one to obtain the drug (CBZ) with predicted structure and morphology should be of great significance for pharmaceutical applications.