Existence of two mature sequences of cubifrin neuropeptide and their effects on spawning in the sea cucumber, Holothuria scabra

NG-related neuropeptide is a myoactive neuropeptide identified in deuterostome invertebrates. Recent studies indicated that in sea cucumbers NG-related neuropeptide can stimulate muscle contraction and is involved in reproduction, including oocyte maturation and gamete spawning. In the present study, we first characterized the NG-related neuropeptide precursor, named cubifrin in Holothuria scabra and further investigated its effect on spawning. The deduced amino acid sequence of the neuropeptide precursor transcript provided five copies of two different mature sequences and were designated as cubifrin-Y and cubifrin-F based on C-terminal amino acid sequences of NGIWYamide and NGIWFamide. Interestingly, physiological bioassay demonstrated that the newly identified cubifrin-F was more potent in stimulating spawning with about 70% success rate, than cubifrin-Y that could stimulate only 10% spawning, compared with the control group. The in situ hybridization showed intense expression of cubifrin transcript within the wall of the ovarian tubule at late ovarian stages, suggesting that cubifrin was produced locally and stimulated spawning by causing contraction of the wall of ovarian tubule. Taken together, gained knowledge provided important insight into spawning mechanisms which could be applied by using these cubifrin amides to stimulate spawning of broodstocks for seed and larval productions in aquaculture of this sea cucumber species.