Biomedical subjects

Jon M Madison

Publications and source records attributed to Jon M Madison.

3 recordsLinked to original sources

PubMed2006

PKC-1 regulates secretion of neuropeptides.

The secretion of neurotransmitters and neuropeptides is mediated by distinct organelles-synaptic vesicles (SVs) and dense-core vesicles (DCVs), respectively. Relatively little is known about the factors that differentially regulate SV and DCV secretion. Here we show that protein kinase C-1 (PKC-1), which is most similar to the vertebrate PKC eta and epsilon isoforms, regulates exocytosis of DCVs in Caenorhabditis elegans motor neurons. Mutants lacking PCK-1 activity had delayed paralysis induced by the acetylcholinesterase inhibitor aldicarb, whereas mutants with increased PKC-1 activity had more rapid aldicarb-induced paralysis. Imaging and electrophysiological assays indicated that SV release occurred normally in pkc-1 mutants. By contrast, genetic analysis of aldicarb responses and imaging of fluorescently tagged neuropeptides indicated that mutants lacking PKC-1 had reduced neuropeptide secretion. Similar neuropeptide secretion defects were found in mutants lacking unc-31 (encoding the protein CAPS) or unc-13 (encoding Munc13). These results suggest that PKC-1 selectively regulates DCV release from neurons.

Aldicarb↗

PubMed2006

Antagonistic regulation of synaptic vesicle priming by Tomosyn and UNC-13.

Priming of synaptic vesicles (SVs) is essential for synaptic transmission. UNC-13 proteins are required for priming. Current models propose that UNC-13 stabilizes the open conformation of Syntaxin, in which the SNARE helix is available for interactions with Synaptobrevin and SNAP-25. Here we show that Tomosyn inhibits SV priming. Tomosyn contains a SNARE motif, which forms an inhibitory SNARE complex with Syntaxin and SNAP-25. Mutants lacking Tomosyn have increased synaptic transmission, an increased pool of primed vesicles, and increased abundance of UNC-13 at synapses. Behavioral, imaging, and electrophysiological studies suggest that SV priming was reconstituted in unc-13 mutants by expressing a constitutively open mutant Syntaxin, or by mutations eliminating Tomosyn. Thus, priming is modulated by the balance between Tomosyn and UNC-13, perhaps by regulating the availability of open-Syntaxin. Even when priming was restored, synaptic transmission remained defective in unc-13 mutants, suggesting that UNC-13 is also required for other aspects of secretion.

Animals↗

PubMed2005

UNC-13 interaction with syntaxin is required for synaptic transmission.

Neurotransmitter secretion at synapses is controlled by several processes-morphological docking of vesicles at release sites, priming of docked vesicles to make them fusion competent, and calcium-dependent fusion of vesicles with the plasma membrane . In worms, flies, and mice, mutants lacking UNC-13 have defects in vesicle priming . Current models propose that UNC-13 primes vesicles by stabilizing Syntaxin's "open" conformation by directly interacting with its amino-terminal regulatory domain . However, the functional significance of the UNC-13/Syntaxin interaction has not been tested directly. A truncated protein containing the Munc homology domains (MHD1 and MHD2) and the carboxy-terminal C2 domain partially rescued both the behavioral and secretion defects of unc-13 mutants in C. elegans. A double mutation in MHD2 (F1000A/K1002A) disrupts the UNC-13/Syntaxin interaction. The rate of endogenous synaptic events and the amplitude of nerve-evoked excitatory post-synaptic currents (EPSCs) were both significantly reduced in UNC-13S(F1000A/K1002A). However, the pool of primed (i.e., fusion-competent) vesicles was normal. These results suggest that the UNC-13/Syntaxin interaction is conserved in C. elegans and that, contrary to current models, the UNC-13/Syntaxin interaction is required for nerve-evoked vesicle fusion rather than synaptic-vesicle priming. Thus, UNC-13 may regulate multiple steps of the synaptic-vesicle cycle.

Amino Acid Sequence↗