A Neurotransmitter Atlas of the Nervous System of C. Elegans Males and Hermaphrodites

Assigning neurotransmitter identity to neurons is key to understanding information flow in a nervous system. It also provides valuable entry points for studying the development and plasticity of neuronal identity features. Neurotransmitter identities have been assigned to most neurons in the C. elegans nervous system through the expression pattern analysis of neurotransmitter pathway genes that encode neurotransmitter biosynthetic enzymes or transporters. However, many of these assignments have relied on multicopy reporter transgenes that may lack relevant cis -regulatory information and therefore may not provide an accurate picture of neurotransmitter usage. We analyzed the expression patterns of 13 CRISPR/Cas9-engineered reporter knock-in strains, which report on the deployment of all main types of neurotransmitters in C. elegans (glutamate, acetylcholine, GABA, serotonin, tyramine, and octopamine) throughout the entire nervous system of both the hermaphrodite and the male. Our analysis reveals novel sites of expression of these neurotransmitter systems within both neurons and glia and defines neurons that may be exclusively neuropeptidergic. Furthermore, we also identified unusual combinations of expression of monoaminergic synthesis pathway genes, suggesting the existence of novel monoaminergic transmitters. Our analysis results in what constitutes the most extensive nervous system-wide map of neurotransmitter usage to date, paving the way for a better understanding of neuronal communication in C. elegans .