A dominant mutation in Snap25 causes impaired vesicle trafficking, sensorimotor gating, and ataxia in the blind-drunk mouse

Abstract

The neuronal soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex is essential for synaptic vesicle exocytosis, but its study has been limited by the neonatal lethality of murine SNARE knockouts. Here, we describe a viable mouse line carrying a mutation in the b-isoform of neuronal SNARE synaptosomal-associated protein of 25 kDa (SNAP-25). The causative I67T missense mutation results in increased binding affinities within the SNARE complex, impaired exocytotic vesicle recycling and granule exocytosis in pancreatic ␤-cells, and a reduction in the amplitude of evoked cortical excitatory postsynaptic potentials. The mice also display ataxia and impaired sensorimotor gating, a phenotype which has been associated with psychiatric disorders in humans. These studies therefore provide insights into the role of the SNARE complex in both diabetes and psychiatric disease.diabetes ͉ mutagenesis ͉ soluble N-ethylmaleimide-sensitive factor attachment protein receptor ͉ schizophrenia ͉ exocytosis I ntracellular membrane fusion events within eukaryotic cells are mediated by proteins of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) family. The prototypic SNARE-mediated fusion event is synaptic vesicle exocytosis, in which the membrane-associated SNAP-25 and syntaxin-1A interact with the vesicle-associated membrane protein (VAMP) to create a stable ternary core complex with 1:1:1 stoichiometry (1). This interaction has been extensively studied in various systems including neurons, neuroendocrine chromaffin cells, and pancreatic ␤-islet cells, all of which use the neuronal core complex proteins to regulate secretion (2, 3). In vivo knockout and mutagenesis studies in invertebrate systems have allowed SNARE function to be analyzed at the level of the synapse (4), but their scope has been limited by the failure of these organisms to model higher neurological functions in which SNARE function is strongly implicated. A major goal, therefore, has been the generation of a mammalian model of SNARE dysfunction in which the effects on complex neurological and behavioral phenotypes can be assessed.Both Vamp2 and Snap25 knockouts are perinatally lethal in homozygous mice, and heterozygotes show no apparent phenotype, so detailed analysis of viable affected individuals has not been possible (5, 6). The spontaneous mouse mutant coloboma carries a heterozygous deletion spanning four genes including Snap25 (7), but its locomotor hyperactivity phenotype is likely to depend on the additional loss of one or more of the other genes within the deleted region. Most recently, a viable syntaxin-1a knockout mouse has been described with subtle defects in long-term potentiation and fear-memory behavior, although normal synaptic transmission is unaffected likely because of functional compensation by syntaxin-1b (8). Existing mammalian SNARE mutations have therefore offered only very limited insights into the consequences of SNARE dysfunction in an adult system and have yielded no informat...

Newcomer insulin secretory granules as a highly calcium-sensitive pool

“…PKC-mediated phosphorylation of SNAP-25 has been shown to increase SNAP-25-syntaxin binding (58), likely resulting in slower SNAP-25-syntaxin dissassembly, which has been suggested to interfere with complete SNARE complex formation, because a syntaxin molecule needs to be replaced by synaptobrevin for formation of the ternary complex (57). Enhanced SNAP-25-syntaxin binding might also hinder full docking of new granules at the IRP release sites, as has been suggested in the blind-drunk mouse, which has a mutation of SNAP-25b that leads to stabilization of the SNARE complex (24,61). SNAP-25 phosphorylation and increased SNAP-25-syntaxin binding may thus account for our hypothesis of decreased full docking rate after PKC activation.…”

Glucose-dependent docking and SNARE protein-mediated exocytosis in mouse pancreatic alpha-cell

“…From our experiments (Fig 2c), it was clear that anti-SNAP-25 reduced both the RRP (by ~45%) and refilling from the RP (~70%). Why the reduction by the SNAP-25 antibody is strongest during mobilisation remains to be answered, but it has earlier been shown that SNAP-25 is of importance for mobilisation of granules [18].…”

Replacing SNAP-25b with SNAP-25a expression results in metabolic disease

“…Indeed, when Sørensen et al (26) separately overexpressed either SNAP-25a or SNAP-25b in embryonic adrenal chromaffin cells from SNAP-25-null mice, the burst of Ca 2+ -evoked catecholamine release differed. Furthermore, impairment of vesicle trafficking and reduced insulin secretion was observed in the blind-drunk mouse, a mutant with a dominant mutation in the SNAP-25b-specific exon, resulting in a further increased stability of the SNARE complex (47). Although SNAP-25a has a lower capacity to keep vesicles in a primed state, little is known how this molecular difference between the splice variants influences animal physiology.…”