Molecular Characterization of the Insulin-Like Androgenic Gland Hormone in the Swimming Crab, Portunus trituberculatus, and Its Involvement in the Insulin Signaling System

The insulin-like androgenic gland hormone (IAG) is mainly produced in the androgenic gland (AG) of the male crustaceans and is a crucial regulator in male sexual differentiation. In the current study, the full-length cDNA of IAG in the swimming crab, Portunus trituberculatus (Pt-IAG), was cloned and characterized. Similar to other reported IAGs, the deduced amino acid sequence of Pt-IAG consists of signal peptide, B chain, C peptide, and A chain, containing six conserved cysteines that form two interchain disulfide bonds and one intra-B chain disulfide bond. Tissue distribution analysis suggested that the Pt-IAG cDNA was highly expressed in the AG and was slightly expressed in several other tissues. A short-term silencing of PtIAG with double-stranded RNA was found to reduce the transcript levels of insulin receptor (Pt-IR) and insulin-like growth factor-binding protein (Pt-IGFBP), suggesting the Pt-IAG might perform its biological function through the insulin family-based signaling system. Bilateral eyestalk ablation (ESA) induced the expression of Pt-IAG in the AG at 4 and 7 days after surgery, while the transcript levels of Pt-IR in the AG and testis and Pt-IGFBP in the muscle, testis, and thoracalia ganglia were significantly decreased from 1 day after surgery. The results suggested that the Pt-IR and Pt-IGFBP might also be the targets of eyestalk neuropeptides and responded to the ESA independent of IAG regulation.