West Coast Worm Meeting Abstracts - Caenorhabditis elegans ...

SEROTONIN SIGNALING IN THE PHARYNX
Timothy Niacaris 1,2 , Leon Avery 1,3
West Coast Worm Meeting 2000
1University of Texas Southwestern Medical Center, Department of Molecular Biology, Dallas, TX
75390-9148
2tim@eatworms.swmed.edu
3leon@eatworms.swmed.edu
Serotonin increases the rate of pharyngeal pumping. This effect occurs by at least two different
mechanisms. Serotonin can indirectly stimulate pharyngeal muscle by increasing the activity of the
pharyngeal motorneuron MC. Serotonin can also act independent of the pharyngeal nervous system to
increase pharyngeal pumping rate, presumably by acting directly on pharyngeal muscle. Serotonin has
two additional MC-independent effects on the pharynx. It decreases the duration of pharyngeal
contractions and enhances the effect of the pharyngeal motorneuron M3. To identify the receptor that
mediates these effects, we have searched the genomic sequence for candidate serotonin receptors and
determined their expression patterns. One strong candidate for mediating the effects of serotonin on
pharyngeal muscle is ser-1. ser-1 is expressed predominantly in pharyngeal muscle and has recently
been determined to be responsive to serotonin in a heterologous expression system 1 . We have isolated
a deletion that eliminates the 3’ end and UTR of ser-1. ser-1(ad1675) truncates the receptor and
eliminates a large portion of the C-terminal intracellular tail, a region important for several aspects of
receptor desensitization. ser-1(ad1675) mutants have an exaggerated response to exogenous serotonin,
consistent with an inability to desensitize in the presence of serotonin. We are currently characterizing
worms defective in other components of the G-protein signaling cascade to identify proteins responsible
for mediating the effects of serotonin on pharyngeal muscle.
1 Hamdan et al. (1999) J. Neurochemistry 72(4):1372-83
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