The claudin-like molecule CLC-3 regulates neuromuscular function in Caenorhabditis elegans by modulating cholinergic signalling

Cell adhesion molecules (CAMs play important roles in neurons, contributing to nervous system development, synapse formation, and activity-dependent plasticity. Claudins, the cell-adhesion molecules known for their roles at tight junctions in epithelial and endothelial cells, remain underexplored in neurons, particularly in vertebrates. In contrast, emerging studies in Caenorhabditis elegans have begun to reveal neuronal functions of claudin-like proteins. However, a systematic analysis of their neuronal expression has not been performed. We conducted a transcriptional reporter screen of all claudin-like genes in C. elegans and identified several candidates with previously unreported neuronal expression, highlighting a broader role of this family in the nervous system. One candidate, clc-3, showed robust expression in head, tail, and ventral cord neurons, with no detectable expression in non-neuronal tissues. Functional analyses of clc-3 mutants revealed increased body-bend amplitude and elevated evoked postsynaptic currents at the cholinergic neuromuscular synapses. Imaging and molecular interaction studies demonstrated that CLC-3 localises to the presynaptic membranes in cholinergic neurons, where it interacts with the actin-binding protein NAB-1 and regulates cholinergic signalling. This presynaptic role of CLC-3 likely contributes to the regulation of sinusoidal movement in C. elegans. Our findings identify CLC-3 as a neuronally expressed claudin that regulates motor system output by influencing synaptic vesicle organization and illustrate how changes in synaptic organization are coupled to whole-animal behaviour.