Kymographic Analysis of Transport in an Individual Neuronal Sensory Cilium in Caenorhabditis elegans

Co-option of neurotransmitter signaling for inter-organismal communication in C. elegans

Biogenic amine neurotransmitters play a central role in metazoan biology, and both their chemical structures and cognate receptors are evolutionarily conserved. Their primary roles are in cell-to-cell signaling, as biogenic amines are not normally recruited for communication between separate individuals. Here, we show that in the nematode C. elegans, a neurotransmitter-sensing G protein-coupled receptor, TYRA-2, is required for avoidance responses to osas#9, an ascaroside pheromone that incorporates the neurotransmitter, octopamine. Neuronal ablation, cell-specific genetic rescue, and calcium imaging show that tyra-2 expression in the nociceptive neuron, ASH, is necessary and sufficient to induce osas#9 avoidance. Ectopic expression in the AWA neuron, which is generally associated with attractive responses, reverses the response to osas#9, resulting in attraction instead of avoidance behavior, confirming that TYRA-2 partakes in the sensing of osas#9. The TYRA-2/osas#9 signaling system represents an inter-organismal communication channel that evolved via co-option of a neurotransmitter and its cognate receptor.

Cell-Specific α-Tubulin Isotype Regulates Ciliary Microtubule Ultrastructure, Intraflagellar Transport, and Extracellular Vesicle Biology

Cilia are found on most non-dividing cells in the human body and, when faulty, cause a wide range of pathologies called ciliopathies. Ciliary specialization in form and function is observed throughout the animal kingdom, yet mechanisms generating ciliary diversity are poorly understood. The "tubulin code"-a combination of tubulin isotypes and tubulin post-translational modifications-can generate microtubule diversity. Using C. elegans, we show that α-tubulin isotype TBA-6 sculpts 18 A- and B-tubule singlets from nine ciliary A-B doublet microtubules in cephalic male (CEM) neurons. In CEM cilia, tba-6 regulates velocities and cargoes of intraflagellar transport (IFT) kinesin-2 motors kinesin-II and OSM-3/KIF17 without affecting kinesin-3 KLP-6 motility. In addition to their unique ultrastructure and accessory kinesin-3 motor, CEM cilia are specialized to produce extracellular vesicles. tba-6 also influences several aspects of extracellular vesicle biology, including cargo sorting, release, and bioactivity. We conclude that this cell-specific α-tubulin isotype dictates the hallmarks of CEM cilia specialization. These findings provide insight into mechanisms generating ciliary diversity and lay a foundation for further understanding the tubulin code.