Definition
Unc-13 homolog C (UNC13C) is a protein-coding gene in the species Homo sapiens that encodes the synaptic protein Munc13‑3, a member of the Munc13 family of vesicle‑priming factors involved in neurotransmitter release at presynaptic terminals.
Overview
UNC13C is located on chromosome 9q34.3 and spans approximately 75 kb of genomic DNA, comprising multiple exons that give rise to several transcript variants. The encoded protein, Munc13‑3, functions as a presynaptic active‑zone component that catalyzes the transition of synaptic vesicles from a docked to a primed state, thereby facilitating calcium‑triggered exocytosis. While UNC13A and UNC13B are broadly expressed throughout the central nervous system, UNC13C displays a more restricted tissue distribution, with higher expression levels reported in the cerebellum, hippocampus, and certain cortical regions. Experimental studies using knockout mice have demonstrated that loss of UNC13C impairs specific forms of short‑term synaptic plasticity and motor coordination, indicating a specialized role in cerebellar circuitry.
Etymology/Origin
The name “Unc‑13” originates from the Caenorhabditis elegans gene unc‑13 (uncoordinated‑13), identified in mutagenesis screens because of locomotor defects. Homologous genes were subsequently discovered in vertebrates and designated UNC13A, UNC13B, and UNC13C to reflect their evolutionary relationship to the original unc‑13 locus. The suffix “C” denotes the third identified paralog within the mammalian UNC13 family.
Characteristics
| Feature | Description |
|---|---|
| Gene ID (NCBI) | 84839 |
| Protein length | Approximately 1,880 amino acids (canonical isoform) |
| Domain architecture | N‑terminal C2A domain, two C2B-like domains, a MUN domain (central to vesicle priming), and a C‑terminal C2C domain |
| Cellular localization | Presynaptic active zones of neuronal terminals; associated with the plasma membrane via diacylglycerol‑binding C1 domains |
| Expression pattern | Enriched in cerebellar granule cells, hippocampal pyramidal neurons, and select cortical interneurons; low to negligible expression in peripheral tissues |
| Biological role | Promotes priming of synaptic vesicles, regulates release probability, and contributes to synaptic plasticity mechanisms such as facilitation and depression |
| Pathophysiological associations | Current literature does not establish a direct causal link between UNC13C mutations and human neurological disease; however, altered expression has been observed in transcriptomic studies of neurodegenerative models, warranting further investigation |
| Orthologs | Conserved across vertebrates (e.g., mouse Unc13c, rat Unc13c) and shares homology with invertebrate unc‑13 proteins |
Related Topics
- Munc13 family – includes UNC13A (Munc13‑1), UNC13B (Munc13‑2), and UNC13D (Munc13‑4), each with distinct tissue distribution and functional specializations.
- Synaptic vesicle cycle – the series of steps encompassing docking, priming, calcium‑triggered fusion, and recycling of neurotransmitter‑filled vesicles.
- Active zone proteins – such as RIM, Bassoon, and Piccolo, which cooperate with Munc13 proteins to organize neurotransmitter release sites.
- Cerebellar neurotransmission – the neural circuitry wherein UNC13C‑mediated vesicle priming plays a notable role in motor coordination.
- Neurogenetics of motor disorders – investigations into how mutations or dysregulation of presynaptic proteins may contribute to ataxia and related phenotypes.