Worm Breeder's Gazette 9(1): 80
We are studying pharyngeal pumping in order to understand the development and function of the nervous system that controls pumping. At the last worm meeting, we described a method for isolating mutants that pump under conditions in which wild-type worms don't. Worms are suspended in liquid with microscopic iron particles; then the worms that have pumped iron are pulled out with a small magnet. Using this selection we have isolated two different sorts of pumping mutants and are now characterizing them. Well-fed wild-type worms pump very little in the absence of bacteria. Three of our mutants do pump under these conditions, so we call them pumping constitutive. One mutation, n1304, is a new allele of unc-31 IV. n1304 has a recessive Unc phenotype similar to that of unc-31( e169), and e169 pumps constitutively. The two alleles fail to complement for both phenotypes. The remaining two mutants look normal in the dissecting microscope. We also have one mutant that pumps in the presence of ivermectin, a drug that normally inhibits pumping and also prevents worms from growing. (We thank Marty Chalfie for telling us about ivermectin.) Although the mutant was selected only for ability to pump in the presence of ivermectin, it also grows on plates containing ivermectin: perhaps the lethal effect of the drug is due entirely to its inhibition of pumping. None of our pumping-constitutive mutants grows on ivermectin plates.