In Vivo Optogenetic Acidification of Synaptic Vesicles in C. elegans

Chemical neurotransmission is a fundamental signaling process found in all animals. Neurotransmitter molecules are packaged into synaptic vesicles, and electrical activity triggers their fusion and release from a pre-synaptic... [ view full abstract ]

Chemical neurotransmission is a fundamental signaling process found in all animals. Neurotransmitter molecules are packaged into synaptic vesicles, and electrical activity triggers their fusion and release from a pre-synaptic cell onto a nearby target cell. The fidelity of this signaling process requires that neurotransmitters are loaded in regular uniform quantities into each synaptic vesicle; however, the mechanisms that control this are not well known. We are testing the hypothesis that the acidic pH created inside synaptic vesicles during the loading process regulates synaptic vesicle fusion. Using novel optogenetic methods we designed a construct with a light-activated proton pump to artificially acidify abnormally alkaline vesicles, combined with an optical pH probe targeted to the vesicular lumen to quantify changes in pH. pH-dependent changes in fluorescence were measured before and after light stimulation using confocal microscopy in immobilized, dissected worm preparations. The analysis of these imaging experiments has involved discovering aspects of our software to maximally detect signal from noise. Here, I will describe the progression of my data analysis, present my current findings on our construct’s capacity to artificially acidify synaptic vesicles, and suggest the implications for our understanding of the regulatory mechanisms of synaptic vesicle loading and fusion.