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

Abstract

22Neuropeptides are secreted molecules that have conserved roles modulating many processes, 23 including mood, reproduction, and feeding. Dysregulation of neuropeptide signaling is also implicated 24 in neurological disorders such as epilepsy. However, much is unknown about the mechanisms 25 regulating specific neuropeptides to mediate behavior. Here, we report that the expression levels of 26 dozens of neuropeptides are up-regulated in response to circuit activity imbalance in C. elegans. acr-2 27 encodes a homolog of human nicotinic receptors, and functions in the cholinergic motoneurons. A 28 hyperactive mutation, acr-2(gf), causes an activity imbalance in the motor circuit. We performed cell-29 type specific transcriptomic analysis and identified genes differentially expressed in acr-2(gf), compared 30 to wild type. The most over-represented class of genes are neuropeptides, with insulin-like-peptides 31 (ILPs) the most affected. Moreover, up-regulation of neuropeptides occurs in motoneurons, as well as 32 sensory neurons. In particular, the induced expression of the ILP ins-29 occurs in the BAG neurons, 33 which are previously shown to function in gas-sensing. We also show that this up-regulation of ins-29 in 34 acr-2(gf) animals is activity-dependent. Our genetic and molecular analyses support cooperative 35 effects for ILPs and other neuropeptides in promoting motor circuit activity in the acr-2(gf) background. 36Together, this data reveals that a major transcriptional response to motor circuit dysregulation is in up-37 regulation of multiple neuropeptides, and suggests that BAG sensory neurons can respond to intrinsic 38 activity states to feedback on the motor circuit. 39 40 41 42 43 44 45 46 2 AUTHOR SUMMARY 47Neuropeptides are secreted small molecules that regulate a variety of neuronal functions and are also 48 implicated in many diseases. However, it remains poorly understood how expression of neuropeptides 49 is regulated, particularly in disease states. Using a genetic animal model that mimics epilepsy, we 50 identified dozens of neuropeptides that are up-regulated when neuronal activities are altered. Some of 51 these neuropeptides share similarity to insulin-like properties (ILPs). Strikingly, one of these ILPs is 52 expressed in sensory neurons that normally respond to acute carbon dioxide exposure. We show that 53 the mis-regulation of this ILP expression is activity-dependent. Moreover, these neuropeptides act in 54 concert to modulate animal behaviors. The findings in this study provide further evidence that 55 neuropeptides are key mediators of aberrant cholinergic signaling, and suggest complex neural network 56 effects from sensory neurons onto motor function. 57 58 59 60 61 62 63 64 65 66 67 68 69 3 Neural circuits are dynamic, changing their properties in response to experience. These 71 changes are critical for maintaining circuit homeostasis and in processes like memory. Many factors 72 such as c-Fos and BDNF, are activated early in response to increased neural activity and further 73 ...

Eukaryotic initiation factor EIF-3.G augments mRNA translation efficiency to regulate neuronal activity

“…6C). As hlh-30 transcripts were detected at similar levels in ACh-MNs of wild type and acr-2 ( gf ) animals (McCulloch et al 2020), the enhanced HLH-30::GFP signal in acr-2 ( gf ) likely reflects elevated translation upon neuronal activity changes, which is augmented by EIF-3.G. We also tested a transgenic HLH-30a::GFP reporter expressing hlh-30a cDNA driven by the 2 kb sequence upstream of that isoform (Fig.…”

“…To address whether EIF-3.G target mRNAs may preferentially affect specific biological processes, we performed Gene Ontology and KEGG pathway analysis. Significant GO term (Ashburner et al 2000) enrichment was identified in neuropeptide signaling genes (GO:0050793; 15 genes), which are known to affect acr-2 ( gf ) behavior (Stawicki et al 2013; McCulloch et al 2020), and in stress response genes (GO: 0006950; 28 genes), which could modulate neuronal homeostasis or function under circuit activity changes (Fig. 5A).…”

“…To determine if expression of EIF-3.G target mRNAs is regulated in an activity-dependent manner, we next incorporated differential transcript expression data between wild type and acr-2 ( gf ) from a cholinergic neuron transcriptome dataset (McCulloch et al 2020). We found that 83% of EIF-3.G target mRNAs in the ACh-MNs are present in the cholinergic neuron transcriptome.…”

“…We studied activity-dependent transcript expression changes among the EIF-3.G target genes (n= 225) by re-analyzing the cholinergic neuron-specific transcriptomes reported in (McCulloch et al 2020) using the Galaxy platform (Afgan et al 2018). We downloaded raw FASTA reads from transcriptome sequencing of wild type and acr-2 ( gf ) animals (n= 2 replicates each; accession #’s SRR10320705, SRR10320706, SRR10320707, SRR10320707) and mapped them to the C. elegans reference genome (ce10) using BWA (Li and Durbin 2009).…”

“…The cholinergic motor neurons (ACh-MNs) in the ventral cord of acr-2 ( gf ) mutants experience constitutive excitatory inputs, which gradually diminish pre-synaptic strength and cause animals to display spontaneous seizure-like convulsions and uncoordinated locomotion (Jospin et al 2009; Zhou et al 2017). acr-2 ( gf ) induces activity-dependent transcriptome changes (McCulloch et al 2020). However, it is unclear how protein translation conducts the activity-dependent proteome changes that sustain function of these neurons.…”