Molecular characterization of an adipokinetic hormone-related neuropeptide (AKH) from a mollusk

Adipokinetic hormones (AKH) are key regulators of energy mobilization in insects. With the growing number of genome sequence available, the existence of genes encoding AKH related peptides has now been established in protostomes. Here we investigated the occurrence of a mature AKH-like neuropeptide (Cg-AKH) in the oyster Crassostrea gigas. We unambiguously elucidated the primary structure of this neuropeptide by mass spectrometry from peptidic extracts of oyster visceral ganglia. Cg-AKH mature peptide (pQVSFSTNWGS-amide) represents an additional member of the AKH family of peptides. The organization of Cg-AKH encoding gene and its corresponding transcript is also described. Cg-AKH gene was found to be expressed in the nervous system though at extremely low levels compared to other neuropeptide encoding genes such as the oyster GnRH gene. Although both reproduction and feeding are known to affect the energy balance in oysters, no significant differential expression of Cg-AKH gene could be evidenced in relation with the nutritional status or along the reproductive cycle. The possible involvement of Cg-AKH in the regulation of energy balance in oyster remains an open question.