Roles of ubiquitin and stress in diacetyl chemosensation of C. elegans

Ubiquitin is a small protein that can be attached to other proteins in a cell, tagging them for destruction. The process of adding ubiquitin to a protein substrate (ubiquitination), and the subsequent trafficking and degradation of this substrate, is a principle regulator of the abundance and activity of many proteins across all forms of life. We are examining the role and dynamics of this regulatory system in the olfactory neurons of the model organism Caenorhabditis elegans, specifically the olfactory receptor protein ODR-10, which allows the worm to detect diacetyl, a volatile compound that is produced by the bacteria the worm eats. Without ODR-10, worms cannot properly perform 'chemotaxis'--detection and movement towards food (Bargmann et al., 1996). Bargmann et al., 1996). Methodology: To further characterize how the ubiquitin degradation pathway functions to regulate the worm's sense of smell and the trafficking of ODR-10, we put worms with ubiquitin pathway mutations under conditions of food stress and compared both their food-seeking behavior and ODR-10 abundance/localization within the AWA neuron to the wild-type strain. The ubiquitin-mediated degradation pathway is known to regulate other cell-surface receptors in neurons (Kowalski et al., 2011), and by testing the diacetyl-sensing ability of worms with mutations in this pathway, we found that abnormal ubiquitination in the ODR-10 expressing neuron ('AWA') leads to reduced diacetyl detection in the worm (Fig. 1) , suggesting that the ubiquitin pathway is indeed involved in regulating ODR-10 (Fig. 2). To further characterize how the ubiquitin degradation pathway functions to regulate the worm's sense of smell and the trafficking of ODR-10, we put worms with ubiquitin pathway mutations under conditions of food stress and compared both their food-seeking behavior and ODR-10 abundance/localization within the AWA neuron to the wild-type strain. We found that while little difference in chemotaxis ability is observed between the mutant strains, the fraction of worms with visible ODR-10 fluorescence varies significantly, suggesting that mechanisms besides ubiquitination to regulate olfaction may be at play.