When C. elegans enters and exits a puddle of liquid, it rapidly switches between distinct crawl and swim patterns of motion as if it were switching between distinct gaits. To identify genes required for the switch from crawl to swim, we screened for mutants that are capable of normal crawling, but incapable of initiating swimming. Although we found many mutants that immediately display an abnormal body waveform and/or bend frequency upon transfer to liquid, we were impressed by one class of mutants that ceased moving, sometimes for minutes, after transfer. This seemed remarkable considering even many severe Unc mutants known to be defective in synaptic transmission move soon after immersion. Once motile, these new mutants also failed to maintain a normal swim pattern. Genetic mapping, complementation testing, and analysis of their shared unique crawling phenotype revealed these were alleles of the fainter genes
unc-79 and
unc-80. Together with Kim Schuske (personal communication) we cloned
unc-80 and found that it is a novel, unusually large, conserved neuronal gene. Through analysis of genomic sequence and reporter expression we found that
unc-79 is also a large, conserved neuronal gene that overlaps in expression with
unc-80. Morgan and Sedensky have previously identified the
unc-79 locus and reported that null mutations in ENaC genes
unc-8 suppresses the fainting phenotype in both
unc-79 and
unc-80. We find that both
unc-79 and
unc-80 overlap in expression with
unc-8. In addition, we find that a fainter allele of
unc-8 exhibits defective swim initiation. Currently we are testing models for the role of the fainter genes in the initiation of swimming.