MOLECULAR-CLONING AND CHARACTERIZATION OF XENOPUS INSULIN-LIKE GROWTH-FACTOR-I RECEPTOR - ITS ROLE IN MEDIATING INSULIN-INDUCED XENOPUS OOCYTE MATURATION AND EXPRESSION DURING EMBRYOGENESIS

We have cloned a complementary DNA encoding the putative Xenopus insul in-like growth factor-1 (xIGF-1) receptor. Injection of messenger RNA derived from the cloned complementary DNA into Xenopus oocytes resulte d in the expression and correct processing of the receptor's alpha- an d beta-subunits. Using antibodies generated against protein expressed against the cloned sequence, we demonstrated that the endogenous xIGF- 1 receptor in Xenopus oocytes was activated by nanomolar concentration s of mammalian IGF-1 and by insulin approximately 100-fold higher in c oncentration. This receptor activation profile correlated with hormone -induced Xenopus oocyte maturation. Furthermore, injection of a neutra lizing antiinsulin receptor antibody into Xenopus oocytes inhibited ho rmone-induced xIGF-1 receptor activation. These results provide molecu lar and biochemical evidence supporting a role for xIGF-1 receptor in mediating insulin/IGF-1-induced Xenopus oocyte maturation. We also rep ort here that embryonic transcription of xIGF-1 receptor is activated during the formation of the central nervous system in early Xenopus em bryos.