C. elegans nematodes sense and respond to other individuals in their environment via signals released by hermaphrodites. The response is sex-specific: males are attracted to the signals and hermaphrodites avoid them. This is interesting because the male and hermaphrodite nervous systems have highly similar anatomy, and the stimulus detected by each is the same--hermaphrodite-derived signals--but the response is opposite. This could arise from (1) sex-specific neurons, (2) sex-specific connectivity of anatomically similar neurons, (3) sex-specific physiology of similar neurons, or (4) a combination of these mechanisms. We are therefore interested in which neurons are necessary and sufficient for male-attraction and hermaphrodite avoidance behaviors.
To determine this, we are using a combination of mutant analysis, neuron-specific rescue, and laser ablation. Avoidance requires
tax-4 and
osm-3. These genes overlap in the ASE, ASG, ASI, ASJ, and ASK pairs. Avoidance behavior is normal in
unc-130 (required for the ASG fate) and in
che-1 (required for proper ASE fate) mutants, indicating that ASI/J/K are most likely necessary for avoidance behavior. Avoidance can be rescued in a
tax-4(
p678) background by
tax-4(+) expression from an
odr-4 promoter, which includes expression in ASG and ASI/J/K but not ASE, indicating that ASI/J/K are sufficient for avoidance. ASI/J/K will be laser-ablated in the rescued strain to show which are necessary. Attraction behavior requires
osm-9. Attraction behavior can be partially rescued in an
osm-9(
ky10) background by
osm-9(+) expression in either male-specific neurons (
pkd-2 promoter), or by expression in the AWB, AWC, and ASI/J/K pairs (
odr-1 or
daf-11 promoters). This indicates these two sets of neurons are each partially sufficient for attraction behavior. Of the second set, attraction is normal in
ceh-36 mutants (required for AWC fate), indicating the AWB and/or ASI/J/K pairs are sufficient for partial rescue. We predict full rescue will be obtained by a combination of expression from the
pkd-2 and
odr-1/daf-11 promoters. Laser ablation will be carried out in the fully rescued strain to show which neurons of the sufficient set are necessary.
It appears, then, that the different sexes may use the same neurons--one or more of the ASI/J/K pair--to generate sex-specific behaviors, but males need at least some input from sex-specific neurons.