FMRFamide-related neuropeptide FLP-3 and FLP-12 regulate head locomotion of C. elegans

Abstract

Neuropeptides regulate behaviors in organisms (Li et al., 2014). However, mechanisms of how neuropeptides are coordinated to generate proper behaviors are not fully understood. In C. elegans, the SMB motor neurons consist of four neurons that innervate head/neck muscles (White et al, 1986) and monitor the amplitude of sinusoidal movement (Gray et al, 2005). The SMB neurons appear to consist of a circuit with the IL1 sensory/inter/motor neurons via the SAA interneurons, and we hypothesized that this SMB-SAA-IL1 circuit may regulate head/neck muscle contraction to modulate head locomotive behaviors. The IL1 and SMB neurons have shown to express FMRFamide-related neuropeptide FLP-3 and FLP-12, respectively. To identify roles of each neuropeptide in head locomotive circuit, we first observed phenotypic consequences of loss of FLP-12 or FLP-3. We tested four locomotive parameters including omega turn, reversal, head lift, and foraging. We found that all four locomotive parameter were increased in flp-12 mutants. We performed rescue experiment and found that expression of flp-12cDNA in SMB successfully four locomotive behaviors. This result indicates that FLP-12 may act in the SMB to regulate head movement . We next found that flp-3 mutants showed increased head lift and foraging, indicating that FLP-3 also regulates head locomotive behaviors. We then tried to identify the receptors for either FLP-12 or FLP-3. Previous study (Frooninckx et al., 2012) suggested that NPR-10 is a putative receptor for FLP-3 whereas receptors for FLP-12 was not identified thus far. To identify receptors for FLP-12, we performed large scale RNAi screening. We examined that which RNAi clone exhibited similar increased foraging behavior to flp-12 mutants and found that knock-down of several genes including FRPR-8 showed similar locomotive defects to flp-12 mutants. We are in progress to generate frpr-8 mutant with CRISPR/Cas9 system. To identify genetic interaction between flp-12 and flp-3, we created flp-12;flp-3 double mutants and found that flp-3;flp-12 mutant showed further increased foraging behavior compared to single mutants, indicating that FLP-12 and FLP-3 act in parallel to regulate foraging behavior.