Molecular characterization of four genes encoding abalone insulin-related peptides and their roles in regulation of hemolymph glucose in the Pacific abalone Haliotis discus hannai

Abstract

Members of the insulin superfamily play key roles in metabolism, growth, reproduction, and longevity via insulin/IGF signaling pathway. The presence of insulin and insulin-related peptides are found among animals. In Mollusca, molluscan insulin-related peptides (MIPs) are involved in their body and shell growth. Hence, this study aimed to understand if there was difference in these peptide levels of fast and slow growing Pacific abalones, Haliotis discus hannai. To this end, four abalone insulin-related peptides (AIPs) are mined from cerebral ganglia transcriptomes of fast-growing and slow-growing abalones: AIP1, −2, −3 and −6. Notably, these AIPs possess 8 cysteine residues in their predicted insulin A and B chains, potentially supporting four disulfide bridges. Further sequence analysis based on the phylogenetic tree and multiple alignment methods indicated that AIPs have sequence features that are conserved among MIPs in many gastropods. The tissue distributions of four AIPs showed ubiquitous and similar expression in the following tissues including the cerebral ganglion, hepatopancreas, gonad, and mantle of both genders. However, there is some difference in other tissue distribution. Since the food consumption is intimately associated with the hemolymph glucose and animal growth, relative AIP1, −2, −3 and − 6 expression levels in the cerebral ganglion were measured following seaweed supplementation. The animals fed with brown seaweed showed increased these AIPs by 1.6–4.7 folds from 3 h after feeding, which lasting to 12 h, coinciding with the peak of hemolymph glucose. Based on these results, we propose that a physiological glucose regulatory mechanism involving AIPs exists in the cerebral ganglion of the H. discus hannai neuroendocrine system.