Tovilla-Loza_2026_Neurosci__

The presynaptic terminal has a complex molecular organization where numerous proteins are involved in various processes, including vesicle trafficking and neurotransmitter release. Calcium ions play a central role in presynaptic function by triggering neurotransmitter release and synaptic vesicle recycling. Here, we investigated the role of two calcium binding proteins, MCTP-1 and ESYT-2, in the synaptic vesicle cycle of Caenorhabditis elegans. Both proteins are widely expressed in the nervous system and colocalize in endoplasmic reticulum subdomains, consistent with membrane contact sites. Loss-of-function mutants for both genes displayed slight defects in motility and similar resistance to acetylcholinesterase inhibition. Recordings of pharyngeal electrical activity revealed that aged (day 6 adult) esyt-2 and mctp-1 single mutants and mctp-1; esyt-2 double mutants exhibit significantly shorter muscle contraction events, but increased pumping rates compared to wild type, indicating altered age-dependent regulation of pharyngeal activity. We also found in an all-optical assay of synaptic transmission and synaptic vesicle recycling, that the endocytic rate was similarly reduced in mctp-1, esyt-2, and mctp-1; esyt-2 loss-of-function worms. Together, these findings show that MCTP-1 and ESYT-2 participate in similar and/or complementary roles, acting within a shared pathway to support efficient synaptic vesicle recycling and to maintain presynaptic function during sustained activity.