Neuronal transcriptome analyses reveal novel neuropeptide modulators of excitation and inhibition imbalance in C. elegans

Abstract

Neuropeptides are secreted molecules that have conserved roles modulating many processes, including mood, reproduction, and feeding. Dysregulation of neuropeptide signaling is also implicated in neurological disorders such as epilepsy. However, much is unknown about the mechanisms regulating specific neuropeptides to mediate behavior. Here, we report that the expression levels of dozens of neuropeptides are up-regulated in response to circuit activity imbalance in C. elegans. acr-2 encodes a homolog of human nicotinic receptors, and functions in the cholinergic motoneurons. A hyperactive mutation, acr-2(gf), causes an activity imbalance in the motor circuit. We performed cell-type specific transcriptomic analysis and identified genes differentially expressed in acr-2(gf), compared to wild type. The most over-represented class of genes are neuropeptides, with insulin-like-peptides (ILPs) the most affected. Moreover, up-regulation of neuropeptides occurs in motoneurons, as well as sensory neurons. In particular, the induced expression of the ILP ins-29 occurs in the BAG neurons, which are previously shown to function in gas-sensing. We also show that this up-regulation of ins-29 in acr-2(gf) animals is activity-dependent. Our genetic and molecular analyses support cooperative effects for ILPs and other neuropeptides in promoting motor circuit activity in the acr-2(gf) background. Together, this data reveals that a major transcriptional response to motor circuit dysregulation is in up-regulation of multiple neuropeptides, and suggests that BAG sensory neurons can respond to intrinsic activity states to feedback on the motor circuit.\n\nAUTHOR SUMMARYNeuropeptides are secreted small molecules that regulate a variety of neuronal functions and are also implicated in many diseases. However, it remains poorly understood how expression of neuropeptides is regulated, particularly in disease states. Using a genetic animal model that mimics epilepsy, we identified dozens of neuropeptides that are up-regulated when neuronal activities are altered. Some of these neuropeptides share similarity to insulin-like properties (ILPs). Strikingly, one of these ILPs is expressed in sensory neurons that normally respond to acute carbon dioxide exposure. We show that the mis-regulation of this ILP expression is activity-dependent. Moreover, these neuropeptides act in concert to modulate animal behaviors. The findings in this study provide further evidence that neuropeptides are key mediators of aberrant cholinergic signaling, and suggest complex neural network effects from sensory neurons onto motor function.