UNC-31/CAPS docks and primes dense core vesicles in C. elegans neurons

Area of Science:

• Neuroscience
• Cell Biology
• Molecular Biology

Background:

• UNC-31, or its mammalian homologue CAPS, is essential for the exocytosis of dense core vesicles (DCVs) and synaptic vesicles (SVs).
• UNC-31 possesses several functional domains, including the dynactin 1 binding domain (DBD), C2, PH, (M)UNC-13 homology domain (MHD), and DCV binding domain (DCVBD).

Purpose of the Study:

• To investigate the specific roles of four functional domains (DBD, C2, PH, MHD, DCVBD) of UNC-31 in exocytosis.
• To determine if full-length UNC-31 or domain-deleted mutants can rescue the UNC-31 null mutant phenotype in C. elegans.

Main Methods:

• Utilized UNC-31 null mutant C. elegans for rescue experiments with full-length and domain-deleted UNC-31 cDNA.
• Conducted physiological studies including locomotion assays, neuromuscular junction neurotransmission analysis, in vivo neuropeptide release measurements, and vesicular docking analysis.

Main Results:

• Full-length UNC-31 rescued the null mutant phenotypes, restoring Ca(2+)-evoked secretion.
• The (M)UNC-13 homology domain (MHD) deletion showed partial rescue, potentially due to high Ca(2+) levels used in specific assays.
• Other domain deletions (DBD, C2, PH, DCVBD) resulted in minimal to no rescue of Ca(2+)-evoked secretion.

Conclusions:

• Each UNC-31 domain plays a distinct role in the sequential process of vesicular exocytosis.
• These domains are involved in critical steps such as vesicle tethering, docking, and priming through SNARE complex formation.