Dopamine (DA) modulates motor function and behavioral plasticity across phylogeny including in C. elegans. The presynaptic DA transporter (DAT) exerts powerful control over DA signaling in terminating DA signaling and limiting DA spillover to extrasynaptic DA receptors. In C. elegans, loss of function
dat-1 mutations results in a hyperdopaminergic paralytic phenotype expressed when worms are placed in water termed Swimming-induced paralysis (Swip). Using Swip as the basis for a forward genetic screen to identify novel regulators of DA signaling, we identified an as yet uncharacterized gene that we designate as
swip-13. Swip-13 mutants display paralysis that is reversed by the VMAT inhibitor reserpine as well as by genetic loss of DA biosynthesis (
cat-2), vesicular packaging (
cat-1) and D2 type DA receptor signaling (
dop-3). Additionally, we find that
swip-13 mutations result in significantly reduced sensitivity to the neurotoxic
dat-1 substrate 6-OHDA, suggesting a possible role for
swip-13 in sustaining DAT-1 protein expression, surface trafficking and/or DA transport activity. Importantly, DA neuron-specific expression of the wild-type
swip-13 gene restores normal swimming behavior in
swip-13 mutants, supporting cell autonomous modulation of DA signaling. Functional, GFP-tagged
swip-13 protein localizes to DA terminals, consistent with a presynaptic contribution to DA signaling. Using a fluorescence recovery after photobleaching (FRAP) approach to monitor DA neuron synaptic vesicle fusion rates, we found that
swip-13 animals display normal basal vesicle fusion. Epistasis studies indicate that
swip-13 and
dat-1 function in the same pathway, possibly via kinase-modulation of DAT-1 trafficking or function. Sequence analysis indicates that SWIP-13 is orthologous to atypical MAP kinases (ERK8 in humans). Excitingly, human DAT protein expression, surface expression and DA transport activity are increased in DAT-transfected SHSY5Y cells effects lost with transfection of a kinase-dead mutant. Ongoing studies seek to elucidate the mechanism by which SWIP-13/ERK8 regulates nematode and mammalian DAT expression and function with an eye to whether kinase function can be manipulated for potential therapeutic benefit in disorders linked to perturbed DA signaling.