The Neuropeptide HGAP Regulates Growth, Reproduction, Metamorphosis, Tissue Damage Repair, and Response against Starvation in Pacific Abalone

Abstract

<b><i>Introduction:</i></b> Neuropeptides regulate vital physiological processes in multicellular organisms, including growth, reproduction, metamorphosis, and feeding. Recent transcriptome analyses have revealed neuropeptide genes with potential roles in vertebrate and invertebrate growth and reproduction. Among these genes, haliotid growth-associated peptide (HGAP) was identified as a novel gene in abalone. <b><i>Methods:</i></b> This study focused on HGAP in Pacific abalone (<i>Haliotis discus hannai</i>), where the complete cDNA sequence named <i>Hdh-HGAP</i> was identified and characterized. Samples from different experiments, such as metamorphosis, juvenile abalone growth, gonad development stages, muscle remodeling, and starvation, were collected for mRNA expression analysis. <b><i>Results:</i></b> The sequence spans 552 bp, encoding 96 amino acids with a molecular weight of 10.96 kDa. Expression analysis revealed that <i>Hdh-HGAP</i> exhibited higher levels in muscle tissue. Notably, during metamorphosis, <i>Hdh-HGAP</i> exhibited greater expression in the trochophore, veliger, and juvenile stages than in the cell division stages. Regarding growth patterns, <i>Hdh-HGAP</i> was highly expressed during rapid growth compared to stunted, minimal, and normal growth. In gonadal development, <i>Hdh-HGAP</i> mRNA reached its highest expression level during the ripening stage, indicating a potential role in gonadal cell proliferation and maturation. The in vivo effects of GnRH on gonad development and the expression of the <i>Hdh-HGAP</i> neuropeptide indicate its involvement in regulating reproduction in Pacific abalone. While tissue remodeling is primarily governed by immune genes, <i>Hdh-HGAP</i> was also upregulated during muscle tissue remodeling. Conversely, <i>Hdh-HGAP</i> was downregulated during prolonged starvation. <b><i>Conclusion:</i></b> This study marks the first comprehensive exploration of the <i>Hdh-HGAP</i> neuropeptide gene in Pacific abalone, shedding light on its involvement in growth, reproduction, metamorphosis, tissue remodeling, and response to starvation, although regulatory mechanisms are mostly unknown.