The Cerebellum-Specific Munc13 Isoform Munc13-3 Regulates Cerebellar Synaptic Transmission and Motor Learning in Mice

Abstract

Munc13 proteins form a family of three, primarily brain-specific phorbol ester receptors (Munc13-1/2/3) in mammals. Munc13-1 is a component of presynaptic active zones in which it acts as an essential synaptic vesicle priming protein. In contrast to Munc13-1, which is present in most neurons throughout the rat and mouse CNS, Munc13-3 is almost exclusively expressed in the cerebellum. Munc13-3 mRNA is present in granule and Purkinje cells but absent from glia cells. Munc13-3 protein is localized to the synaptic neuropil of the cerebellar molecular layer but is not found in Purkinje cell dendrites, suggesting that Munc13-3, like Munc13-1, is a presynaptic protein at parallel fiber-Purkinje cell synapses. To examine the role of Munc13-3 in cerebellar physiology, we generated Munc13-3-deficient mutant mice. Munc13-3 deletion mutants exhibit increased paired-pulse facilitation at parallel fiber-Purkinje cell synapses. In addition, mutant mice display normal spontaneous motor activity but have an impaired ability to learn complex motor tasks. Our data demonstrate that Munc13-3 regulates synaptic transmission at parallel fiberPurkinje cell synapses. We propose that Munc13-3 acts at a similar step of the synaptic vesicle cycle as does Munc13-1, albeit with less efficiency. In view of the present data and the well established vesicle priming function of Munc13-1, it is likely that Munc13-3-loss leads to a reduction in release probability at parallel fiber-Purkinje cell synapses by interfering with vesicle priming. This, in turn, would lead to increases in pairedpulse facilitation and could contribute to the observed deficit in motor learning.

Target-Dependent Feedforward Inhibition Mediated by Short-Term Synaptic Plasticity in the Cerebellum

“…However, we observed a sevenfold difference in their absolute inhibitory strengths (BC 3 PC, 1.73 Ϯ 0.55 nA; SC 3 PC, 0.24 Ϯ 0.04 nA), which would be mostly attributable to the different size of the presynaptic terminals (Palay and ChanPalay, 1974). Munc13-3 KO mice did not change the depression time course at the BC 3 PC synapse (n ϭ 3; data not shown), confirming that Munc13-3 was not involved in inhibitory synaptic transmission (Augustin et al, 2001). …”

“…To gain additional insights of the difference between GC 3 BC and GC 3 SC synapses, we studied knockout (KO) mice of Munc13-3, a presynaptic protein implicated in synaptic vesicle priming (Augustin et al, 1999;Basu et al, 2007). Deletion of Munc13-3, a cerebellar-specific isoform of Munc13 (Augustin et al, 2001), has been shown to induce an increase of paired-pulse facilitation in granule cell 3 Golgi cell synapses (Beierlein et al, 2007). We observed an increase of the pairedpulse facilitation also in GC 3 BC synapse ( Fig.…”

A novel method for detecting uniparental disomy from trio genotypes identifies a significant excess in children with developmental disorders

“…While channelopathies often follow a dominant mode of inheritance (Koch et al 1993), recessive modes have been seen as well (Trip et al 2008), and several channel proteins are known to underlie severe seizure disorders, such as KCNQ2 (Ohtahara syndrome) (Yamatogi and Ohtahara 2002) and paralogs of SCN4A, such as SCN1A (Wolff et al 2006), SCN2A (Kearney et al 2001), and SCN9A (Singh et al 2009). In addition, the child has compound heterozygous missense mutations in UNC13C, a gene known to result in an inability to learn complex motor tasks in mouse knockouts (Augustin et al 2001).…”

<b>Inhibitory role of Munc13-1 in antigen-induced mast cell </b><b>degranulation </b>

“…For the knockdown of rat Munc13-1, the target sequences 5′-GCGGC TGAGAAGAGTTCTA-3′ (KD1) and 5′-GCAAC AAGCCTGAGATCTT-3′ (KD2) were obtained using Invitrogen BLOCK-iT RNAi designer (http:// The Munc13 family comprises the following five proteins: Munc13-1, bMunc13-2, and Munc13-3, which were originally identified as neuronal isoforms, uMunc13-2, which was identified as a ubiquitously expressed splicing variant of bMunc13-2, and Munc13-4, which was identified as a non-neuronal isoform (20). Munc13-1, u/bMunc13-2, and Munc13-3 are involved in neurotransmitter release as expected (2,3,23,32); however, Munc13-1 is also required for insulin secretion in pancreatic β cells (21). On the other hand, Munc13-4 is involved in regulated exocytosis in hematopoietic secretory cells, such as cytotoxic T lymphocytes (CTLs), platelets, neutrophils, and mast cells (7,12,27,30,33,35).…”