Abstract
Wild sea cucumber resources have been rapidly exhausted and therefore there is an urgent need to develop approaches that will help restocking. Currently, there is a lack of information regarding the genes involved in sea cucumber reproductive processes. The neurohormone relaxin-like gonad-stimulating peptide (RGP) has been identified as the active gonad-stimulating peptide in sea stars (Asteroidea), which could also be present in other echinoderm groups. In this study, a sea cucumber RGP was identified and confirmed by phylogenetic analysis. A recombinant Holothuria scabra RGP was produced in the yeast Pichia pastoris and confirmed by mass spectrometry. To assess bioactivity, four levels of purification were tested in an in vitro germinal vesicle breakdown (GVBD) bioassay. The most pure form induced 98.56 ± 1.19% GVBD in H. scabra and 89.57 ± 1.19% GVBD in Holothuria leucospilota. Cruder levels of purification still resulted in some GVBD. Upon single injection into female H. scabra, the recombinant RGP induced head waving behavior followed by spawning within 90–170 min. Spawned oocytes were fertilized successfully, larvae settled and developed into juveniles. Our results provide a key finding for the development of a break-through new artificial breeding approach in sea cucumber aquaculture.
Highlights
Sea cucumbers are widely considered as commercially valuable with a high demand for consumption and use in some traditional medicines (Olivera-Castillo et al, 2013; Fahmy et al, 2015)
relaxin-like gonad-stimulating peptide (RGP) and insulin-like growth factor (IGF) share the conservation of amino acid residues within the A- and B-chain regions, especially the conserved cysteine residues which are potentially important for disulphide bridge formation, variable amino acids were observed throughout the mature peptide length
Cross-species in vitro oocyte maturation experiments showed that both Asterias amurensis RGP (AamRGP) and Aphelasterias japonica RGP (AjaRGP) could not induce oocyte maturation and ovulation in the ovary of P. pectinifera, the PpeRGP was active in ovaries of A. amurensis and A. japonica (Mita, 2016)
Summary
Sea cucumbers are widely considered as commercially valuable with a high demand for consumption and use in some traditional medicines (Olivera-Castillo et al, 2013; Fahmy et al, 2015). Artificial breeding has become an effective solution to produce high quality seed for aquaculture, stock enhancement, and sea ranching. Spawning induction is a critical procedure in artificial breeding, traditional stimulation methods such as thermal shock, drying rehydration, exposure. Sea Cucumber Relaxin-Like Gonad-Stimulating Peptide to conspecific sperm, and a combination of the aforementioned treatments (Al Rashdi et al, 2012) are not efficient. Traditional stimulation methods are thought to reduce the health of broodstock. The employment of reproductive neuropeptide hormones for achieving reproductive maturation and spawning is an innovative approach with great potential to advance hatchery production in sea cucumber aquaculture
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