RIM and MUNC13 membrane-binding domains are essential for neuropeptide secretion

Area of Science:

• Neuroscience
• Cell Biology
• Molecular Biology

Background:

• Neurons utilize synaptic vesicles (SVs) and dense-core vesicles (DCVs) for releasing neurotransmitters and neuropeptides, respectively.
• Presynaptic proteins RIM and MUNC13 are known to be crucial for SV exocytosis, but their role in DCV release is less understood.

Purpose of the Study:

• To investigate the distinct mechanisms by which RIM and MUNC13 regulate dense-core vesicle (DCV) exocytosis compared to synaptic vesicle (SV) exocytosis.
• To determine the specific roles of different protein domains within RIM and MUNC13 in DCV targeting and release.

Main Methods:

• Neuropeptide secretion assays with single-vesicle resolution.
• Peptidomics analysis of endogenous neuropeptide release in MUNC13/RIM null neurons.
• Investigation of protein-lipid interactions and proteasomal degradation pathways.

Main Results:

• MUNC13 is demonstrated to be essential for DCV exocytosis.
• The RIM N terminus protects MUNC13 from proteasomal degradation, and its inhibition partially rescues DCV exocytosis in RIM-deficient neurons.
• Specific membrane-binding domains in RIM and MUNC13 exhibit differential regulation of DCV exocytosis, with the MUNC13 C2C domain being crucial, unlike in SV exocytosis.

Conclusions:

• RIM and MUNC13 synergistically control DCV exocytosis via specific membrane interactions.
• Mechanistic differences exist between SV and DCV exocytosis regulation by RIM and MUNC13 proteins.