Dopamine-dependent, swimming-induced paralysis arises as a consequence of loss of function mutations in the RUNX transcription factor RNT-1

Abstract

Dopamine (DA) is a neurotransmitter with actions across phylogeny that modulate core behaviors such as motor activity, reward, attention, and cognition. Perturbed DA signaling in humans is associated with multiple disorders, including addiction, ADHD, schizophrenia, and Parkinson’s disease. The presynaptic DA transporter exerts powerful control on DA signaling by efficient clearance of the neurotransmitter following release. As in vertebrates, Caenorhabditis elegans DAT (DAT-1) constrains DA signaling and loss of function mutations in the dat-1 gene result in slowed crawling on solid media and swimming-induced paralysis (Swip) in water. Previously, we identified a mutant line, vt34 , that exhibits robust DA-dependent Swip. vt34 exhibits biochemical and behavioral phenotypes consistent with reduced DAT-1 function though vt34; dat-1 double mutants exhibit an enhanced Swip phenotype, suggesting contributions of the vt34 -associated mutation to additional mechanisms that lead to excess DA signaling. SNP mapping and whole genome sequencing of vt34 identified the site of the molecular lesion in the gene B0412.2 that encodes the Runx transcription factor ortholog RNT-1. Unlike dat-1 animals, but similar to other loss of function rnt-1 mutants, vt34 exhibits altered male tail morphology and reduced body size. Deletion mutations in both rnt-1 and the bro-1 gene, which encodes a RNT-1 binding partner also exhibit Swip. Both vt34 and rnt-1 mutations exhibit reduced levels of dat-1 mRNA as well as the tyrosine hydroxylase ortholog cat-2 . Although reporter studies indicate that rnt-1 is expressed in DA neurons, its re-expression in DA neurons of vt34 animals fails to fully rescue Swip. Moreover, as shown for vt34 , rnt-1 mutation exhibits additivity with dat-1 in generating Swip, as do rnt-1 and bro-1 mutations, and vt34 exhibits altered capacity for acetylcholine signaling at the neuromuscular junction. Together, these findings identify a novel role for rnt-1 in limiting DA neurotransmission and suggest that loss of RNT-1 may disrupt function of both DA neurons and body wall muscle to drive Swip.

Allosteric Modulator KM822 Attenuates Behavioral Actions of Amphetamine in Caenorhabditis elegans through Interactions with the Dopamine Transporter DAT-1

“…Hardaway et al, 2015;J. A. Hardaway et al, 2012;Robinson et al, 2019;Safratowich et al, 2013). The free-living C. elegans hermaphrodite possesses 8 mechanosensitive DA neurons that inhibit motor neurons involved in determining the speed of crawling on solid surfaces or thrashing in liquid.…”

“…We and others have made use of the nematode model to study DAT-dependent DA signaling (Bermingham et al, 2017;Carvelli et al, 2010;J. A. Hardaway et al, 2012;Nass et al, 2002;Robinson et al, 2019).…”

Sink or swim: Does a worm paralysis phenotype hold clues to neurodegenerative disease?

“…Apart from the DA neuron cell‐autonomous role for rnt‐1 in producing Swip, the gene appears to have roles in other cell types. In fact, rnt‐1 (vt34) exhibits altered synaptic transmission capacity as demonstrated by aldicarb and levamisole assays, suggesting a disrupted ACh signaling at neuromuscular junctions (Robinson et al, 2019). Although Runx transcription factors have well‐established roles in neural development, postmitotic neural functioning, and support of damaged neural tissue in mammals (Wang & Stifani, 2017), these findings are the first to demonstrate a role for proteins of this class in the regulation of DA signaling.…”

“…Line vt34(Robinson et al, 2019) was found to encode a mutant allele of the C. elegans gene encoding the Runt-related (Runx) transcription factor, rnt-1, which functions as a dimer with the protein encoded by bro-1, whose mutation also was found to cause Swip. Reduced levels of dat-1 and cat-2 expression were observed in rnt-1 mutants, indicative of the role of rnt-1 in defining limits to DA signaling.…”

The dopamine membrane transporter plays an active modulatory role in synaptic dopamine homeostasis

“…Deletion of dat‐1 causes accumulation of extracellular dopamine into the synaptic cleft resulting in a swimming‐induced paralysis (SWIP) behavioral phenotype (Hardaway et al., 2012; McDonald et al., 2007). Dynamic regulation of the dat‐1 gene influences DAT‐1 expression and is likely to modulate behavioral effects observed by its deletion (Felton & Johnson, 2014; Robinson et al., 2019).…”