TY - JOUR T1 - Titration of Syntaxin1 in Mammalian Synapses Reveals Multiple Roles in Vesicle Docking, Priming, and Release Probability JF - The Journal of Neuroscience JO - J. Neurosci. SP - 16698 LP - 16714 DO - 10.1523/JNEUROSCI.0187-13.2013 VL - 33 IS - 42 AU - Marife Arancillo AU - Sang-Won Min AU - Stefan Gerber AU - Agnieszka Münster-Wandowski AU - Yuan-Ju Wu AU - Melissa Herman AU - Thorsten Trimbuch AU - Jong-Cheol Rah AU - Gudrun Ahnert-Hilger AU - Dietmar Riedel AU - Thomas C. Südhof AU - Christian Rosenmund Y1 - 2013/10/16 UR - http://www.jneurosci.org/content/33/42/16698.abstract N2 - Synaptic vesicles undergo sequential steps in preparation for neurotransmitter release. Individual SNARE proteins and the SNARE complex itself have been implicated in these processes. However, discrete effects of SNARE proteins on synaptic function have been difficult to assess using complete loss-of-function approaches. We therefore used a genetic titration technique in cultured mouse hippocampal neurons to evaluate the contribution of the neuronal SNARE protein Syntaxin1 (Stx1) in vesicle docking, priming, and release probability. We generated graded reductions of total Stx1 levels by combining two approaches, namely, endogenous hypomorphic expression of the isoform Stx1B and RNAi-mediated knockdown. Proximity of synaptic vesicles to the active zone was not strongly affected. However, overall release efficiency of affected neurons was severely impaired, as demonstrated by a smaller readily releasable pool size, slower refilling rate of primed vesicles, and lower release probability. Interestingly, dose–response fitting of Stx1 levels against readily releasable pool size and vesicular release probability showed similar Kd (dissociation constant) values at 18% and 19% of wild-type Stx1, with cooperativity estimates of 3.4 and 2.5, respectively. This strongly suggests that priming and vesicle fusion share the same molecular stoichiometry, and are governed by highly related mechanisms. ER -