Molecular characterization and growth-associated role of schistosomin-like peptide in Pacific abalone (Haliotis discus hannai)

Neuropeptides secreted from the central nervous system regulate diverse physiological processes in mollusks. Although schistosomin-like peptide (SLP) has been reported in tropical abalone, its biological role remains unclear. In this study, we isolated and characterized the Hdh -SLP gene from Pacific abalone ( Haliotis discus hannai ) and examined its expression under multiple physiological conditions, including development, growth, aging, reproduction, intersex transition, tissue regeneration, starvation and refeeding, and thermal stress. The full-length Hdh -SLP cDNA was 405 bp and encoded a 74-amino-acid cysteine-rich secreted peptide with predicted neurotoxin-like and ion channel-blocking properties. Hdh -SLP was predominantly expressed in the pleuropedal ganglion. Its expression increased during the larval-to-juvenile transition, was higher in rapidly growing juveniles than in stunted individuals and declined with age. Expression also increased during masculinization and showed stage- and sex-dependent variation during gonadal development. Functional silencing of Hdh -SLP significantly downregulated major growth-related factors, including Hdh -MIRP1, Hdh -HGAP, and Hdh -MLGF, indicating that this neuropeptide primarily acts as a positive regulator of somatic growth. In addition, Hdh -SLP was upregulated during tissue regeneration but downregulated under prolonged starvation and extreme heat stress. Collectively, these findings provide the first comprehensive characterization of Hdh -SLP in Pacific abalone and identify this neuropeptide as a potential regulator of growth and physiological adaptation, with possible relevance for growth improvement strategies in abalone aquaculture.