Differential expression of neuropeptides correlates with growth rate in cultivated Haliotis asinina (Vetigastropoda: Mollusca)

Rapid and efficient growth of animals in culture is critical to the success of most aquaculture industries. For example, the commercial cultivation of highly-prized abalone (Haliotidae: Vetigastropoda) has been hampered by naturally slow growth rates. To begin to investigate the molecular mechanisms controlling growth in haliotid molluscs, we chose to focus on neuropeptides secreted from anterior brain ganglia, because these have been implicated in controlling growth and reproduction in non-commercial gastropods. Here, we report the characterisation of three neuropeptides expressed in the anterior cerebral and pleuropedal ganglia of the tropical abalone Haliotis asinina; these are (1) the evolutionarily-conserved molluscan insulin-like peptide (Has-MIP), (2) a gastropod-specific schistosomin-like peptide (Has-SLP) and (3) a novel peptide currently known only from abalone, which we have called the haliotid growth-associated peptide (Has-HGAP). The novel Has-HGAP gene encodes a prepropeptide that undergoes substantial post-translational processing, including cleavage at an unusual site separating the two mature peptide chains of 19 and 51 amino acids in length; these are covalently bound by disulfide bonds. Quantitative comparison of Has-HGAP, Has-SLP and Has-MIP transcript abundance between the fastest and slowest growing individuals within a cohort of 6 month old cultured H. asinina reveals that Has-HGAP and Has-SLP are significantly upregulated in fast growing abalone; in contrast, Has-MIP is significantly downregulated. In light of their differential expression among juvenile abalone with markedly different growth rates, we suggest these neuropeptide genes will be fruitful points of focus for improving H. asinina growth rates in aquaculture by marker-assisted selective breeding