Abstract
In an attempt to understand growth regulation in Japanese eel, Anguilla japonica, we cloned insulin-like growth factor-I (IGF-I) cDNAs and examined their expression in several tissues. Two Japanese eel IGF-I cDNAs encoding preprohormones, eIGF-I-Ea 1 and eIGF-I-Ea 2, were cloned from the liver by PCR. Both preprolGF-Is shared identical signal peptides and mature IGF-I domains but contained different E domains. Upon sequence comparison, eel IGF-I showed higher sequence identity with other fish. The eIGF-I-Ea 1 mRNA was detected mainly in the liver by RT-PCR and higher eIGF-I-Ea 1 mRNA levels were observed in females and larger sized eel. In contrast, eIGF-I-Ea 2 mRNA was detected at relatively lower levels in all of the examined tissues with females and larger sized fish exhibiting higher levels. Incubation of liver slices with recombinant eel growth hormone at concentrations of 10 to 1, 000 ng/ml for 24 hr resulted in a significant increase in both eIGF-l mRNA levels in a concentration-dependent manner. These results suggest that IGF-I is involved in the regulation of somatic growth in the eel.
