Serotonin and dopamine act antagonistically to modulate egg-laying behaviour in C. elegans. Serotonin signals via the G-coupled serotonin receptor SER-1 in the vulval muscle to stimulate egg-laying, but the mode of the inhibitory action of dopamine remains largely unknown. To date three dopamine receptors have been identified in C. elegans, one D1 like (
dop-1) and two D2 like (
dop-2,
dop-3). No dopamine receptor has yet been implied in the egg-laying paradigm (1,2). MOD-1 was originally characterised as an ionotropic serotonin receptor controlling the rate of locomotion of C. elegans in response to food. Surprisingly, MOD-1 appears to be essential for the inhibitory action of dopamine on egg-laying.
mod-1 (
ok103) deletion mutants continue to lay eggs in the presence of dopamine and following prolonged starvation (3). Inhibitory dopaminergic signaling via MOD-1 is restricted to the egg-laying paradigm as
mod-1 (
ok103) mutants are still susceptible to paralysis induced by dopamine. In order to determine the role and pathway of MOD-1 in this dopamine signalling pathway we are conducting a genetic screen for mutants resistant to dopamine inhibition of egg-laying. Our screen will use the following approach: F2 progeny of singled ethylmethane sulfonate mutagenized animals are exposed to 5 mg/ml serotonin and 3 mg/ml dopamine.
mod-1 (
ok103) mutants continue to lay eggs under such treatment whereas egg-laying in wild-type animals is inhibited. We have recovered several mutants that show similar dopamine resistance as
mod-1 (
ok103) mutants. 1. Sanyal, S., Wintle, R. F., Kindt, K. S., Nuttley, W. M., Arvan, R., Fitzmaurice, P., Bigras, E., Merz, D. C., Hebert, T. E., van der Kooy, D., Schafer, W. R., Culotti, J. G. & Van Tol, H. H. M. (2004) Embo Journal 23, 473-482. 2. Chase, D. L., Pepper, J. S. & Koelle, M. R. (2004) Nature Neuroscience 7, 1096-1103. 3. Dempsey, C. M. Mackenzie S. M., Gargus A., Blanco G. & Sze J. Y. (2005).. Genetics (In press).