Fusion of lipid bilayers in cells facilitates the active transport of chemicals. Non-viral membrane fusion is regulated by a cascade of proteins as the process is highly regulated both in space and... Show moreFusion of lipid bilayers in cells facilitates the active transport of chemicals. Non-viral membrane fusion is regulated by a cascade of proteins as the process is highly regulated both in space and time. In eukaryotic cells, the so-called SNARE protein complex is at the heart of fusion. However, little is known about the actual mechanism at the molecular level. Inspired by the SNARE protein complex, our group previously developed a model system composed of a pair of lipidated complementary coiled coil peptides enabling targeted liposome-liposome fusion. This model system possesses all the key characteristics of membrane fusion similar to SNARE mediated fusion. The tetrameric coiled-coil of SNAREs is mimicked by a complementary pair of coiled coil forming peptides composed of three heptad repeat units (denoted __coil-E__ and __coil-K__). A flexible poly(ethylene glycol) spacer is conjugated to the N-terminus ensuring rotational freedom of the peptides. Lipidation warrants the anchoring of the peptides in the membrane by means of a phospholipid anchor (DOPE), mimicking the transmembrane domain of SNAREs. In order to develop future applications of this model system, the mechanism of membrane fusion needs to be studied in more detail and this has been the goal of this thesis. Show less
Fitzsimons, C.P.; Hooijdonk, L.W.A. van; Schouten, M.; Zalachoras, I.; Brinks, V.; Zheng, T.; ... ; Vreugdenhil, E. 2013
Glucocorticoids (GCs) secreted after stress reduce adult hippocampal neurogenesis, a process that has been implicated in cognitive aspects of psychopathology, amongst others. Yet, the exact role of... Show moreGlucocorticoids (GCs) secreted after stress reduce adult hippocampal neurogenesis, a process that has been implicated in cognitive aspects of psychopathology, amongst others. Yet, the exact role of the GC receptor (GR), a key mediator of GC action, in regulating adult neurogenesis is largely unknown. Here, we show that GR knockdown, selectively in newborn cells of the hippocampal neurogenic niche, accelerates their neuronal differentiation and migration. Strikingly, GR knockdown induced ectopic positioning of a subset of the new granule cells, altered their dendritic complexity and increased their number of mature dendritic spines and mossy fiber boutons. Consistent with the increase in synaptic contacts, cells with GR knockdown exhibit increased basal excitability parallel to impaired contextual freezing during fear conditioning. Together, our data demonstrate a key role for the GR in newborn hippocampal cells in mediating their synaptic connectivity and structural as well as functional integration into mature hippocampal circuits involved in fear memory consolidation. Show less
