Dopamine (DA) signaling modulates multiple behaviors including patterned motor activity, reward seeking and executive function. The cocaine-sensitive DA transporter (DAT) is a critical determinant of presynaptic DA homeostasis as well as in limiting the actions of DA in space and time. Consequentially, disrupted DA signaling is thought to contribute to risk for multiple brain disorders including schizophrenia, attention-deficit hyperactivity disorder (ADHD), addiction and Parkinson's disease. Unfortunately, forward genetic approaches that can elucidate the molecular networks impinging on the control of DA signaling and DAT are difficult to implement in mammals. We have found that ablation of the C. elegans dat-1 gene results in a highly-penetrant, DA signaling-dependent, paralysis phenotype when worms are placed in water, a phenotype we term Swimming- Induced Paralysis (Swip). The Swip of dat-1 animals can be rescued by crosses to animals bearing loss of function alleles of cat-1, ortholog of mammalian vesicular monoamine transporters (VMATs), cat-2, which encodes tyrosine hydroxylase, as well as by treatment of animals with the VMAT inhibitor reserpine. Rescue of Swip behavior is also seen when dat-1 animals are crossed to animals lacking a specific, postsynaptic D2-type dopamine receptor (dop-3). Recently, our lab implemented a forward genetic screen to identify Swip lines that can be rescued by reserpine as well as by crosses to other DA signaling mutants. From this screen, I have helped identify animals bearing novel, loss of function dat-1 alleles, as well as mutants that map to loci that lac known contributors to DA signaling. One such mutant, swip13 (vt32), displays reduced DA levels, similar to dat-1 knockout animals, and exhibits resistance to the neurotoxin 6-OHDA, which requires DAT-1 activity for DA neuron import. As Swip is a hyperdopaminergic phenotype, the reduced DA content of swip13 (vt32) animals and loss of 6-OHDA sensitivity suggest that the SWIP13 protein may regulate DAT expression, trafficking or activity. I have recently identified the gene accounting for the swip13 phenotype, and found it to be highly conserved in mammals. Here, I propose to investigate how this swip13 regulates DA signaling in C. elegans with Blakely lab and collaborative studies examining the relatively unstudied swip13 ortholog ERK 7/8.
Dysfunction of central dopaminergic systems in humans is associated with a number of disorders including addiction, attention-deficit hyperactivity disorder (ADHD), schizophrenia, bipolar disorder, and Parkinson's disease. We have utilized the model system Caenorhabditis elegans and a dopamine-mediated behavior known as Swimming-induced paralysis (Swip) to perform a forward genetics screen to identify and characterize genes involved in regulating dopamine signaling. One gene generated by the screen, swip13, has clear mammalian homologs and the proposed research plan seeks to characterize the role this gene and its orthologs play in regulating dopamine signaling in C. elegans, and through collaborative studies, in mammals.
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