SNARE-dependence of the exocytosis at the inner hair cell ribbon synapse

点击翻译按钮获取中文摘要

The sensory systems provide the organism with Information about the extemal world. Acoustic information, for example, is processed by the auditory system involving transduction of mechanical stimuli by hair cells of the cochlea. Finally acoustic information is encoded at the ribbon synapses of the inner hair cells (lHCs). Although molecular biological and biophysical works have initiated major progress in investigating ribbon synapse, its molecular physiology is still poorly understood. Work of this DFG-funded project has raised the provocative question whether this synapse employs the archetypical neuronal SNARE complex. During exocytosis in most synapses, a four-helical coiled-coil protein complex is formed between the three SNARE proteins syntaxin 1, synaptobrevin 2 and SNAP-25. It bridges vesicle and plasma membrane and has been implied from docking to fusion step of exocytosis. During the first funding period Regis Nouvian has made the striking observation that exocytosis in IHCs is resistant to clostridial neurotoxins E and D, which in many other neurosecretory preparations interfere with exocytosis by cleaving SNAP-25 and synaptobrevin, respectively. Moreover, a mouse mutant with a loss of function mutafion in the synaptobrevin 1 gene showed normal IHC exocytosis, which was unexpected, given that synaptobrevin 1 had been formely identified in guinea pig IHCs. When exploring the expression of SNAREs in mouse IHCs we did not find consistent evidence for the expression of neuronal SNAREs. The objective of this grant renewal is to identify the SNAREs involved in IHC exocytosis by further experiments on the expression of SNAREs (single-cell PCR, immunohistochemistry and analysis of knock-in mice for fluorescently tagged variants of SNAREs) and by further testing the effects of clostridial neurotoxins. This work will be performed in Göttingen in collaboration with Regis Nouvian, who initiated this study but will move on to take a CNRS position in Montpellier at the end of 2008 before this project can be completed.