Regulation of WNT Signaling at the Neuromuscular Junction by the Immunoglobulin Superfamily Protein RIG-3 inCaenorhabditis elegans

Abstract

Perturbations in synaptic function could affect the normal behavior of an animal, making it important to understand the regulatory mechanisms of synaptic signaling. Previous work has shown that in Caenorhabditis elegans an immunoglobulin superfamily protein, RIG-3, functions in presynaptic neurons to maintain normal acetylcholine receptor levels at the neuromuscular junction (NMJ). In this study, we elucidate the molecular and functional mechanism of RIG-3. We demonstrate by genetic and BiFC (Bi-molecular Fluorescence Complementation) assays that presynaptic RIG-3 functions by directly interacting with the immunoglobulin domain of the nonconventional Wnt receptor, ROR receptor tyrosine kinase (RTK), CAM-1, which functions in postsynaptic body-wall muscles. This interaction in turn inhibits Wnt/LIN-44 signaling through the ROR/CAM-1 receptor, and allows for maintenance of normal acetylcholine receptor, AChR/ACR-16, levels at the neuromuscular synapse. Further, this work reveals that RIG-3 and ROR/CAM-1 function through the β-catenin/HMP-2 at the NMJ. Taken together, our results demonstrate that RIG-3 functions as an inhibitory molecule of the Wnt/LIN-44 signaling pathway through the RTK, CAM-1.

Control of Locomotory Behavior of Caenorhabditis elegans by the Immunoglobulin Superfamily Protein RIG-3

“…RIG-3 is expressed in AVA command interneurons and a small number of pharyngeal interneurons as well as in cholinergic motor neurons (Schwarz et al 2009;Babu et al 2011). Previous studies have also shown that RIG-3 functions at the neuromuscular junction, where it has been reported to regulate the acetylcholine receptor delivery (Babu et al 2011;Pandey et al 2017). Our results suggest that animals lacking rig-3 show more frequent spontaneous reversals in comparison to WT control animals ( Figure 1).…”

“…Studies have shown that RIG-3 plays an important role in maintaining acetylcholine receptor levels at the neuromuscular junction (Babu et al 2011;Pandey et al 2017). Apart from showing expression in cholinergic motor neurons, RIG-3 also shows expression in the anterior region that is thought to be restricted to the command interneuron AVA and pharyngeal neurons (Schwarz et al 2009).…”

“…One such IgSF member, RIG-3, is expressed in the reversal circuitry neuron AVA, pharyngeal neurons I1, I4, M4 and NSM, and cholinergic motor neurons (Schwarz et al 2009;Babu et al 2011). Previous work has described the role of RIG-3 at the neuromuscular junction, where it has been shown to maintain the acetylcholine receptor ACR-16 (Babu et al 2011;Pandey et al 2017). However, although RIG-3 shows expression in the AVA command interneuron, its function in AVA remains largely unknown.…”

Claudins in the brain: Unconventional functions in neurons

“…Their study shows that ACR‐16/α7 receptor translocation is mediated by members of the canonical Wnt signaling pathway . Out of five Wnts LIN‐44, EGL‐20, CWN‐1, CWN‐2 and MOM‐2 in C. elegans , CWN‐2 and LIN‐44 are involved in this pathway. The Wnts, CWN‐2 and LIN‐44 secreted from the presynaptic neurons, bind and activate the postsynaptic Wnt receptor Lin‐17/Frizzled.…”

“…Most of the excitatory currents at the C. elegans NMJs are mediated by nicotine‐sensitive ACR‐16/α7 (nAChR) receptors. The surface expression of these receptors is regulated through the Wnt signaling pathway . Jensen et al have elegantly dissected out the Wnt signaling pathway, which regulates the translocation of ACR‐16/α7 receptors at the C. elegans NMJs.…”