No abstract

CNS synapse assembly typically follows after stable contacts between "appropriate" axonal and dendritic membranes are made. We show that presynaptic boutons selectively form de novo following neuronal fiber adhesion to beads coated with poly-D-lysine (PDL), an artificial cationic polypeptide. As demonstrated by atomic force and live confocal microscopy, functional presynaptic boutons self-assemble as rapidly as 1 h after bead contact, and are found to contain a variety of proteins characteristic of presynaptic endings. Interestingly, presynaptic compartment assembly does not depend on the presence of a biological postsynaptic membrane surface. Rather, heparan sulfate proteoglycans, including syndecan-2, as well as others possibly adsorbed onto the bead matrix or expressed on the axon surface, are required for assembly to proceed by a mechanism dependent on the dynamic reorganization of F-actin. Our results indicate that certain (but not all) nonspecific cationic molecules like PDL, with presumably electrostatically mediated adhesive properties, can effectively bypass cognate and natural postsynaptic ligands to trigger presynaptic assembly in the absence of specific target recognition. In contrast, we find that postsynaptic compartment assembly depends on the prior presence of a mature presynaptic ending.

Hydrophobe Quantenpunkte können in die Doppelschichtmembran von Lipidvesikeln eingeschlossen und von dort selektiv in Plasmamembranen oder in das Cytoplasma lebender Zellen freigesetzt werden (siehe Bild). Die Zell‐ und Lipidmembranen können jede Art von hydrophoben Nanopartikeln einschließen, deren Größe mit der Membrandicke übereinstimmt, was Möglichkeiten für Einzelzellanwendungen in der Nanobiotechnologie bietet.

Spherical supported bilayer membranes (SS-BLMs) are very attractive candidates in modern bioanalytics and biorecognition studies. A uniform, facile method of preparing different SS-BLMs on silica beads is reported. Confocal fluorescence microscopy and cryo-TEM imaging have been used to characterize these SS-BLMs. Thermal analysis data and FRAP experiments show that the bilayer properties of the SS-BLM are consistent with those of lipid vesicles from which they are formed. The possibility of modulating the size, lipid type and functionality, and mechanical stability makes these rigid liposomes very attractive candidates in biosensors, drug screening, and gene delivery-related applications. This is especially true in work with native vesicle membranes derived from living cells because the existing methods can only accommodate anionic membranes to a limited extent.