title: The Anaphase-Promoting Complex (APC) ubiquitin ligase regulates GABA transmission at the C. elegans neuromuscular junction.
abstract: Regulation of both excitatory and inhibitory synaptic transmission is critical for proper nervous system function. Aberrant synaptic signaling, including altered excitatory to inhibitory balance, is observed in numerous neurological diseases. The ubiquitin enzyme system controls the abundance of many synaptic proteins and thus plays a key role in regulating synaptic transmission. The Anaphase-Promoting Complex (APC) is a multi-subunit ubiquitin ligase that was originally discovered as a key regulator of protein turnover during the cell cycle. More recently, the APC has been shown to function in postmitotic neurons, where it regulates diverse processes such as synapse development and synaptic transmission at glutamatergic synapses. Here we report that the APC regulates synaptic GABA signaling by acting in motor neurons to control the balance of excitatory (acetylcholine) to inhibitory (GABA) transmission at the Caenorhabditis elegans neuromuscular junction (NMJ). Loss-of-function mutants in multiple APC subunits have increased muscle excitation at the NMJ; this phenotype is rescued by expression of the missing subunit in GABA neurons. Quantitative imaging and electrophysiological analyses indicate that APC mutants have decreased GABA release but normal cholinergic transmission. Consistent with this, APC mutants exhibit convulsions in a seizure assay sensitive to reductions in GABA signaling. Previous studies in other systems showed that the APC can negatively regulate the levels of the active zone protein SYD-2 Liprin-α. Similarly, we found that SYD-2 accumulates in APC mutants at GABAergic presynaptic sites. Finally, we found that the APC subunit EMB-27 CDC16 can localize to presynapses in GABA neurons. Together, our data suggest a model in which the APC acts at GABAergic presynapses to promote GABA release and inhibit muscle excitation. These findings are the first evidence that the APC regulates transmission at inhibitory synapses and have implications for understanding nervous system pathologies, such as epilepsy, that are characterized by misregulated GABA signaling.
authors: Department of Biological Sciences, Butler University, Indianapolis, IN 46208 USA. Electronic address: jrkowals@butler.edu.
authors: Jennifer R
authors: JR
authors: Kowalski
authors: Department of Biological Sciences, Butler University, Indianapolis, IN 46208 USA. Electronic address: hdube@butler.edu.
authors: Hitesh
authors: H
authors: Dube
authors: Department of Neurobiology, University of Massachusetts Medical School, Worcester, MA 01605, USA. Electronic address: Denis.Turutin@umassmed.edu.
authors: Denis
authors: D
authors: Touroutine
authors: Department of Biological Sciences, Butler University, Indianapolis, IN 46208 USA. Electronic address: kmrush@butler.edu.
authors: Kristen M
authors: KM
authors: Rush
authors: Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Boston, MA 02111, USA. Electronic address: pgoodwin@brandeis.edu.
authors: Patricia R
authors: PR
authors: Goodwin
authors: Department of Biological Sciences, Butler University, Indianapolis, IN 46208 USA. Electronic address: mcarozza@indiana.edu.
authors: Marc
authors: M
authors: Carozza
authors: Department of Biological Sciences, Butler University, Indianapolis, IN 46208 USA. Electronic address: Zpdid01@louisville.edu.
authors: Zachary
authors: Z
authors: Didier
authors: Department of Neurobiology, University of Massachusetts Medical School, Worcester, MA 01605, USA. Electronic address: Michael.Francis@umassmed.edu.
authors: Michael M
authors: MM
authors: Francis
authors: Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, Boston, MA 02111, USA. Electronic address: peter.juo@tufts.edu.
authors: Peter
authors: P
authors: Juo
mesh_terms: D064173:Anaphase-Promoting Complex-Cyclosome / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D017173:Caenorhabditis elegans / Q000378:metabolism* / Q000502:physiology; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism; D059330:GABAergic Neurons / Q000378:metabolism* / Q000502:physiology; D036341:Intercellular Signaling Peptides and Proteins; D009046:Motor Neurons / Q000378:metabolism / Q000502:physiology; D009154:Mutation; D009469:Neuromuscular Junction / Q000378:metabolism* / Q000502:physiology; D010750:Phosphoproteins / Q000378:metabolism; D021381:Protein Transport; D009435:Synaptic Transmission; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D029742:Caenorhabditis elegans Proteins; D036341:Intercellular Signaling Peptides and Proteins; D010750:Phosphoproteins; C490598:SYD-2 protein, C elegans; D005680:gamma-Aminobutyric Acid; D064173:Anaphase-Promoting Complex-Cyclosome
keywords: Anaphase-Promoting Complex; GABA; NMJ; Synapse; Ubiquitin ligase