Localization of the SUMO Conjugating Enzyme UBC-9 in C. elegans Neurons

The nervous system relies on tight regulation of proteins to maintain a balance of excitatory to inhibitory signaling for proper function. SUMO (small ubiquitin-like modifier) polypeptides are attached to cellular proteins by the UBC-9 conjugating enzyme, thereby regulating such functions as neuronal signaling. The molecular mechanisms by which SUMOylation affects neuronal signaling balance remain unknown, yet multiple neuronal proteins are SUMOylated, including several implicated in neurodegenerative diseases. I imaged transgenic worms expressing fluorescently tagged UBC-9 to investigate where UBC-9 is expressed in neurons and whether this enzyme colocalizes with the Caenorhabditis elegans SUMO polypeptide (SMO-1) at neuromuscular synapses. My hypothesis is that UBC-9 acts in presynaptic motor neurons to control signaling via its SUMO-conjugating activity. I constructed a UBC-9 strain that fluoresces green in inhibitory motor neurons and crossed it to a strain in which inhibitory synapses fluoresce red. Imaging results indicate that green UBC-9 overlaps with red synaptic vesicle proteins, suggesting UBC-9 can localize to neuromuscular synapses. Additional imaging of strains in which SMO-1 fluoresces green and synapses fluoresce red are underway. UBC-9 and SMO-1 strains will eventually be crossed and imaged to see if the two proteins also colocalize. Future studies will investigate whether the UBC-9 catalytic site is required for UBC-9\u27s effects on neuromuscular signaling and identify UBC-9 substrates. Given the similarities between C. elegans and mammalian nervous systems, understanding how SUMO enzymes control the balance of normal neuronal signaling may provide important information related to human neurobiology and contribute to research on diseases of imbalanced signaling