IGFBP7 is involved in abalone metamorphosis

Metamorphosis is the most critical life stage for abalone. There are morphogenetic transformations and habitat selection with metamorphosis. A large amount of larvae often die during this stage. Insulin/insulin-like growth factor signaling pathway (IIS) plays a role in the development. However, there is little knowledge of IIS function in metamorphosis. IGFBP7, a component of IIS, was found to be involved in metamorphosis of small abalone Haliotis diversicolor. The expression of saIGFBP7 mRNA rapidly increased before metamorphosis, which were mainly localized in the velum and foot. There was a significant decrease of metamorphosis rate after competent larvae were exposed to 5 μg/mL dsRNA of saIGFBP7 (p = 2.50 × 10− 10, F = 389.05). The expressions of three downstream genes of IIS (PI3K, ERKα and AKT) as well as saIGFBP7 were decreased in the dsRNA exposure experiment. There was no significant difference of metamorphosis rate (p = 0.97, F = 0.071) after competent larvae were induced in different concentrations of insulin. The expression of saIGFBP7, PI3K and ERKα also had no significant difference in insulin inducing assay. However, AKT expression level of 1 μmol/L insulin induced group was significantly higher than that of other concentrations (p = 3.41 × 10− 7, F = 26.68). These results suggested that IGFBP7 is involved in metamorphosis of abalone larvae. Our study provides insight on developing new methods for increasing the metamorphosis rate in abalone aquaculture. However, it does not work as a negative regulator of IIS activity, or plays its role in an IGF- and insulin-independent manner during metamorphosis of abalone larvae.