Neuropeptides are important modulators that are packaged into dense core vesicles (DCVs) in the soma and released from specialized release sites upon neural stimulation. However, the mechanisms underlying DCV biogenesis, maturation and secretion are poorly understood. We found that the anterior body wall muscle contraction (aBoc) is controlled, in part, by the FMRFamide neuropeptide-like protein FLP-22, which is secreted from AVL and functions as an excitatory neurotransmitter to elicit aBoc. We identified multiple alleles of the leucine rich repeat kinase 1 and 2 (LRRK1/2) ortholog
lrk-1 in a forward genetic screen for positive regulators of aBoc.
lrk-1 null mutants have normal pacemaker-evoked calcium entry into AVL but show a late-onset aBoc defect in the adult stage, and exhibit an accumulation of FLP-22-containing DCVs in AVL axons. Both defects of
lrk-1 mutants can be fully rescued by AVL-specific expression of wild type
lrk-1 but not kinase-dead
lrk-1 cDNA. The aBoc defects of
lrk-1 mutants can be fully rescued by Channelrhodopsin-induced AVL activation, and can be partially rescued by phospho-mimetic mutations in either
unc-57/endophilin or
rab-10/Rab10 loci generated by CRISPR knock-in. Loss of
unc-57 or
unc-26/synaptojanin function (but not of other endocytic components) suppress the aBoc defects of
lrk-1 mutants whereas null mutations in
rab-10 fail to suppress the aBoc defects of
lrk-1 mutants. The phospho-mimetic mutant of
unc-57(S75D) can restore wild type DCVs abundance in AVL axons to
lrk-1 mutants, while the phospho-dead mutant (S75A) fails to do so. Together, using aBoc as a new model for neuropeptide-controlled signaling, we propose that LRK-1 promotes DCVs secretion by regulating DCV membrane components through phosphorylation of at least two targets: UNC-57, which leads to PIPs level change through UNC-26; and RAB-10, which affects its own activity to further regulate downstream effectors.