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FP6

NEURORECYCLING Résumé de rapport

Project ID: 42267
Financé au titre de: FP6-MOBILITY
Pays: Belgium

Final Activity Report Summary - NEURORECYCLING (Maintaining neurotransmission : clathrin-mediated endocytosis and kiss-and-run)

Our brain consists of over a 100 billion neurons, organised into neuronal circuits that transmit electrical pulses. Hence, the integrity of a circuit depends on reliable neuronal communication: if a neuron fails, the circuit fails. The importance to maintain neuronal communication is underscored by numerous psychiatric disorders, such as schizophrenia, epilepsy and drug addiction arising from defects in specific circuits. Neurons in these circuits communicate by releasing neurotransmitters from synaptic vesicles and to maintain communication neurons dependent on efficient recycling of synaptic vesicle pools. The work within this Marie Curie Excellence Team has focused on understanding the mechanisms of vesicle recycling using morphological and functional assays. Synapses communicate by releasing neurotransmitters. This process is determined by the fusion of synaptic vesicles with the membrane. When numerous vesicles fuse, endocytosis of synaptic vesicles at the membrane is critical to generate sufficient new vesicles to maintain release. This project has provided novel key insight into the molecular mechanisms of synaptic vesicle formation.

By analysing the localisation and function of specific lipids at the synapse, studies in the Excellence team identified PI(4,5)P2 as a critical lipid in the formation of synaptic vesicles. A novel protein Tweek appears to be critically involved in the process, and further studies also indicate that this same protein, is a gatekeeper of synaptic growth through an action that involves PI(4,5)P2 localisation. Thus these data link synaptic endocytosis and lipid metabolism to synaptic development. Similarly, the assembly of endocytic pits and clathrin cages where synaptic vesicles form is also linked to phosphoinositide metabolism. However, the function of clathrin and many of the accessory proteins had not been studied in vivo in detail.

In this project, not only was clathrin itself found to be essential for vesicle recycling, and unexpectedly found to be inhibitory to membrane uptake, it was also found that critical modifications (eg phosphorylation) of proteins involved in vesicle formation are important regulators of synaptic vesicle formation. Thus, studies by the Marie Curie Excellence Team have provided key novel insight into synaptic vesicle formation at synapses. Studies in the Marie Curie Excellence Team also aimed to analyse mechanisms of alternative synaptic vesicle recycling pathways. Whereas in clathrin-mediated endocytosis (CME) membranes invaginate to form vesicles, in kiss-and-run, vesicles form a transient fusion pore and recycle locally; however, the existence of alternative vesicle recycling modes like kiss-and-run or bulk retrieval remains controversial, because no specific protein required for them had been identified.

In this project the Marie Curie Excellence team has therefore employed a novel innovative genetic strategy to isolate the first molecular components of these alternative recycling pathways. More than 40 novel mutants have been identified in this screen, and these mutants are very good candidates for further analyses towards understanding novel recycling routes. Thus, work in the Marie Curie Excellence team has not only provided novel molecular insight into the mechanisms of synaptic vesicle formation in clathrin dependent endocytosis, but it has also paved the way towards a better understanding of novel, previously unstudied alternative recycling routes that may be operational at the synapse.

Taken together, studies in the Marie Curie Excellence Team seek to elucidate mechanisms of vesicle retrieval. By understanding processes underlying neuronal communication better, the future aim is to gain valuable insight into the basis of normal and pathological brain function.

Contact

Bart DE STROOPER
Tél.: +32-1-6346227
Fax: +32-1-6347181
E-mail