A transposon insert in domain 3a of Munc18-1 inhibits spontaneous and asynchronous release

Random transposon mutagenesis has generated several Munc18-1 mutants, reported to affect their binding efficiency for Syntaxin1 and Mint1. Here, we tested a mutant containing a transposon insert in a helix of domain 3a, M18L307, on its ability to support synaptic transmission in autaptic munc18-1 null neurons. These neurons showed reduced spontaneous and asynchronous release, faster synaptic depression, and delayed post-train recovery. In addition, synaptic Munc18-1 levels were reduced by a factor of two in mutant compared to control neurons, which is known to increase synaptic depression. These results implicate domain 3a in several aspects of synaptic vesicle release. Since spontaneous release is affected to a larger extent than evoked release, a role downstream of priming is suggested, potentially in regulating vesicular release probability. The increased Mint affinity reported for M18L307 hints at a potential contribution of Mint to the synaptic transmission defects reported in this study. 73 74 CHAPTER 5 5.1 5.