Hyperglycemia that is caused by the release of
crustacean hyperglycemic hormone (CHH) from the sinus gland to hemolymph is one of the hallmark physiological phenomena, occurring in decapod crustaceans experiencing stressful conditions. However, the mechanism(s) by which such elevated
glucose levels return to resting levels is still unknown. Interestingly, noted is a difference in the clearance rate of hemolymph
glucose between adult females and adult males of the blue crab, Callinectes sapidus: the former with more rapid clearance than the latter. The presence of an endogenous-
insulin-like molecule is suggested in C. sapidus because an injection of bovine
insulin, significantly reduces the levels of hemolymph
glucose that were previously elevated by emersion stress or the
glucose injection. Using 5' and 3' RACE, the full-length
cDNA of an
insulin-like molecule is isolated from the hepatopancreas of an adult female C. sapidus and shows the same putative sequence of an
insulin-like androgenic gland factor (IAG) but differs in 5' and
3' UTR sequences. A knock-down study using five
injections of
double-stranded RNA of CasIAG-hep (dsRNA-CasIAG-hep, 10μg/injection) over a 10-day period reduces CasIAG-hep expression by ∼50%. The levels of hemolymph
glucose are also kept higher in dsRNA-CasIAG-hep injected group than those treated with dsRNA-
green fluorescent protein (dsRNA-IAG-hep) or saline. Most importantly, the hepatopancreas of dsRNA-CasIAG-hep injected animals contains amounts of
carbohydrate (
glucose,
trehalose, and
glycogen) significantly lower than those of control groups, indicating that the function of CasIAG-hep in carbohydrate metabolism in crustaceans is similar to carbohydrate metabolism in vertebrates.