2004 West Coast Worm Meeting abstract 78
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| 1 | Dept.of Biological Sciences, University of Illinois at Chicago, IL, 60607. |
| 2 | Dept of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville 37232. |
C. elegans body wall muscles have two pharmacologically distinct acetylcholine receptors (AChR) ( Richmond and Jorgensen, 1999): a levamisole-sensitive receptor that contains UNC-38, UNC-63, UNC-29 and LEV-1 subunits and a previously unidentified nicotine-sensitive receptor that is selectively blocked by DHbE.
To identify components of the non-levamisole-sensitive receptor, we examined an Affymetrix microarray data set obtained from FACS-isolated myo-3::GFP muscle cells. ACR-16 mRNA was among several nAChR subunits found to be enriched in muscle. Ballivet et.al. (1996) have shown that heterologously expressed ACR-16 forms a functional homomeric receptor that pharmacologically resembles the native non levamisole-sensitive receptor in C. elegans body wall muscle.
To test whether ACR-16 contributes to the ACh response in body wall muscle, we have characterized a deletion mutant obtained from the knockout consortium, acr-16(ok789). This mutant does not exhibit obvious locomotion defects. However, electrophysiological recordings revealed that the ACh response is reduced by 88% in acr-16(ok789) compared to the wild type. Similarly, the nicotine response is reduced by 87%, whereas the levamisole response is unaffected. These electrophysiological defects can be fully rescued by expressing ACR-16 under the control of the myo-3 promoter in muscles. Evoked responses in acr-16 (ok789) are also dramatically reduced (86%), suggesting that activation of the ACR-16 receptor contributes the majority of peak evoked response.
We have made double mutants between acr-16 (ok789) and the levamisole receptor subunit mutants unc-29 and unc-63. These double mutants have a more severe uncoordinated phenotype than either unc-63 or unc-29 mutants alone and the muscle ACh response is reduced by 98% relative to wildtype. These results suggest that both, the levamisole-receptor and the ACR-16 dependent receptor contribute to locomotion in C. elegans.