Non-equilibrium fluctuations in GUVs driven by light

From more than one century ago to nowadays one of the main challenges in neurobiology is the understanding the basis of memory. The locus that was discovered to be the storage of memories in the mammalian brain, where the synapses are built on, are the dendritic spines. The relation between molecular, morphological data of dendritic spines and memory formation with relative diseases has been extensively investigated, nevertheless many mechanisms are still poorly understood. One of these is the compartmentalisation, a term that involves the confinement of membrane-bound receptors in the head of spines and it is believed to underlie the changes in synaptic strength during learning and memory formation. One process proposed to explain the compartmentalisation is the presence of domains that trap the receptors from the surrounding. In this work a biomimetical model was built to study the problem of the receptors confinement in dendritic spines. By micromanipulation it is possible to model the spines with a wellcontrollable system in vitro made of one-layer lipid membranes with a spherical shape, named Giant Unilamellar Vesicles, (GUVs) and tubules. From previous studies it is known that when GUVs are prepared with lipids of different transition temperatures, at a critical composition, as the temperature is lowered, phase separation in Liquid Ordered (Lo) and Liquid Disordered (Ld) phases occurs. In this work, a novel cutting-edge technique to obtain the phase separation is employed in a systematic way and the response of the GUVs is characterised in term of physical parameters. Briefly, the temperature is kept constant, and the composition of the vesicles changed using light, via photo-oxidation. Varying the ratio between the lipids that prefer the Lo and Ld phases until the critical composition is reached, it is possible to control the process and induce the phase separation for one vesicle of a time. In this way, the phase separated domains of the GUVs are used to model the compartments in the spines and quantum dots were added to the previous system mimic the receptors. It is worthy to highlight the importance of using a biomimetic model to study this problem. It is a way to look in the heart of the process with different eyes, aimed not to neglect the detail of the system, but to provide a solid basis that allows to include all of them later and study the real problem with its complexity.