Modulation of Gq-Rho Signaling by the ERK MAPK Pathway Controls Locomotion in Caenorhabditis elegans

Abstract

The heterotrimeric G protein Gq regulates neuronal activity through distinct downstream effector pathways. In addition to the canonical Gq effector phospholipase Cβ, the small GTPase Rho was recently identified as a conserved effector of Gq. To identify additional molecules important for Gq signaling in neurons, we performed a forward genetic screen in the nematode for suppressors of the hyperactivity and exaggerated waveform of an activated Gq mutant. We isolated two mutations affecting the MAP kinase scaffold protein KSR-1 and found that KSR-1 modulates locomotion downstream of, or in parallel to, the Gq-Rho pathway. Through epistasis experiments, we found that the core ERK MAPK cascade is required for Gq-Rho regulation of locomotion, but that the canonical ERK activator LET-60/Ras may not be required. Through neuron-specific rescue experiments, we found that the ERK pathway functions in head acetylcholine neurons to control Gq-dependent locomotion. Additionally, expression of activated LIN-45/Raf in head acetylcholine neurons is sufficient to cause an exaggerated waveform phenotype and hypersensitivity to the acetylcholinesterase inhibitor aldicarb, similar to an activated Gq mutant. Taken together, our results suggest that the ERK MAPK pathway modulates the output of Gq-Rho signaling to control locomotion behavior in.

Dynamic neurotransmitter specific transcription factor expression profiles during Drosophila development

“…The enrichment of MAP kinase pathway regulators in cholinergic neurons is intriguing, suggesting that this signalling pathway may have a specific role in these neurons. This is supported by a recent study showing that MAP kinase signalling acts downstream of Gq-Rho signalling in C. elegans cholinergic neurons to control neuron activity and locomotion (Coleman et al, 2018).…”

A role for the Erk MAPK pathway in modulating SAX-7/L1CAM-dependent locomotion in Caenorhabditis elegans

“…A recent study uncovered a novel neuronal role for ksr-1 (C oleman et al 2018). Specifically, loss-of-function ksr-1 alleles were isolated in a genetic screen for suppressors of the hyperactive and loopy locomotion exhibited by activated Gq/EGL-30 animals.…”

“…Specifically, loss-of-function ksr-1 alleles were isolated in a genetic screen for suppressors of the hyperactive and loopy locomotion exhibited by activated Gq/EGL-30 animals. Moreover, ksr-1 expression restricted to a subset of cholinergic neurons in the head of egl-30; ksr-1 animals was sufficient to reverse this suppression; in contrast, ksr-1 expression in ventral nerve cord cholinergic neurons in the body did not (C oleman et al 2018).…”

“…Head cholinergic neurons comprise a subset of motor neurons that synapse on muscles in the head region as well as interneurons that synapse onto ventral nerve cord motor neurons to coordinate locomotion (W hite et al 1986; P ereira et al 2015). The MAPK pathway was previously discovered to also modulate locomotion mediated by the heterotrimeric G protein Gq (C oleman et al 2018). Hyperactive Gq signaling results in aberrant loopy locomotion that is also dependent on KSR-1 function in head cholinergic neurons.…”

“…Each transgene was inserted into the oxTi365 MoSCI site present in the EG8082 strain (F rokjaer -J ensen et al 2014). To do so, we injected each of corresponding ksr-1- containing MosSCI plasmids (pBC31, pBC32 and pBC33 (C oleman et al 2018)) individually at 50ng/μl along, along with a cocktail containing 50ng/ul each of sgRNA-containing vectors pXW7.01 and pXW7.02 (gift of Katya Voronina, University of Montana) to cleave the universal ttTi5605 MosSCI site, and 2.5ng/μl of selection marker pCFJ90 (P myo-2 ::mCherry). Injected animals were incubated at 25°C for approximately 7 days, after which non-Unc, non-fluorescent F2 progeny were individually picked and screened for stable transmission of non-Unc, non-fluorescent progeny.…”