Pharyngeal muscle relaxation is normally very fast: in the corpus, it is probably complete in less than 20 msec. The speed of relaxation is regulated by the pharyngeal nervous system, and if relaxation isn't fast enough, bacteria aren't efficiently trapped and transported. Muscarinic acetylcholine agonists and mutations in the genes
eat-4 ,
eat-6 ,and
eat-12 slow and inhibit pharyngeal relaxation. In the hope of identifying more genes involved in the control of relaxation, we tested 14 feeding-defective mutants for hypersensitivity to the agonists arecoline. One of them,
eat-11 (
ads4)I, was hypersensitive: it was killed by 1 mM arecoline, a concentration that barely affects wild type. In the absence of drugs,
eat-11 produces only a mild phenotype: the corpus is weakly defective in transporting bacteria. (Under some conditions, however, some
eat-11 larvae arrest at L1 ,an observation whose significance we are unsure of.)
eat-11 worms are also slightly longer than normal, and they have slightly abnormal movement: bends are deeper than normal. To identify more genes that affect the response of muscle to acetylcholine, we isolated about 20
eat-11 suppressors by selecting for growth of F2 self-progeny of mutagenized hermaphrodites on 5 mM arecoline. Our analysis has concentrated on the seven strongest, all of which are dominant suppressors of
eat-11 arecoline hypersensitivity and semi-dominant suppressors of the visible phenotypes. In addition, they produce phenotypes of their own. All turn out to be gain-of-function mutations in the gene
egl-30 .
egl-30 (gf)mutations arose at frequencies of one in a few thousand. The following table summarizes our observations and those of Trent et al (Genetics 104: 619) and Park and Horvitz (Genetics 113: 821): [See Figure] The phenotypes of the gain-of-function alleles are consistent with a defect in egg-laying, pharyngeal, and body wall muscles, weakest in
ad803 and
ad806 ,and strongest in
ad810 .The flaccid paralysis phenotype of
ad805 ,
ad809 ,
ad814 ,and surviving
n715 homozygotes is very similar to that of
unc-54 or
unc-15 mutants.
ad810 and
ad813 arrest growth at hatching, and have no (
ad810 )or very feeble (
ad813 )body wall, defecation, and pharyngeal muscle movements. They are flaccid, unlike lethals such as
unc-104 or
cha-1 that lack nervous system function. Two observations suggest that the gain-of-function phenotype is not caused by a defect in muscle contractile structures per se. First, no other muscle-defective mutations were isolated as
eat-11 suppressors. Since such mutations are common,
egl-30 (gf)mutations must have some effect other than the reduction of muscle contraction. Second, the early, nervous system independent embryonic movement that occurs during elongation is normal in
ad810 embryos, unlike mutants such as
myo-3 that lack all body wall muscle contraction. A model that reconciles all these observations is that
egl-30 (gf)mutations block a pathway by which muscles respond to acetylcholine, e.g. by preventing membrane excitation. our guesses as to
eat-11 'srole are even vaguer: one possibility is that it is necessary for desensitization of the response to acetylcholine. We may be able to test these ideas for pharyngeal muscle by measuring EPGs in
egl-30 and
eat-11 mutants (see Raizen and Avery, this WBG).