G Proteins A Salty Sensation

The nematode Caenorhabditis elegans is particularly useful for studying heterotrimeric GTP-binding protein (G protein) function, because of its comparative genetic simplicity: C. elegans has only 2 G and 2 Gβ subunits, compared to mammals, which have 12 G and 5 Gβ subunits. Furthermore, sensory perception can be analyzed with simple behavioral assays for chemotactic response. Jansen et al. generated G (gpc-1) knockout and G-overexpressing worms and established an adaptation assay for water-soluble compounds, or taste sensation. Altering GPC-1 by either deletion or overexpression did not change initial chemotactic responses to volatile (smell) or water-soluble (taste) attractants or repellants. However, worms lacking GPC-1 did not adapt to continued presence of salts, such as sodium chloride, sodium acetate, or ammonium chloride. Adaptation responses to volatile agents were normal. Taste adapation was also impaired in mutants of adp-1 and osm-9, two genes implicated in adaptation to odorants. Thus, adaptation to particular smells and tastes may involve common signaling mechanisms. GPC-1 was not expressed in the neurons responsible for salt detection (ASE neurons), but instead was expressed in the ASI neurons, which are synaptically coupled to the ASE neurons. Thus, the role of G in adaptation may be to alter ASE neuron activity through changes in the synaptic activity of ASI.

G. Jansen, D. Weinkove, R. H. A. Plasterk, The G-protein subunit gpc-1 of the nematode C. elegans is involved in taste adaptation. EMBO J. 21, 986-994 (2002). [Abstract] [Full Text]