Expression of the IGF-II/mannose-6-phosphate receptor mRNA and protein in the developing rat

The insulin-like growth factor II (IGF-II) receptor is identical to the mannose-6-phosphate receptor (M-6-P), but its role as a somatomedin transducer is uncertain. IGF-II/M-6-P receptor expression was studied by in situ hybridization (ISH) in the developing rat. Expression occurs in extra-embryonic membranes at the time of IGF-II mRNA induction and later at paracrine/autocrine sites of IGF-II action (skeletal muscle and perichondrium) in the embryo. Highest levels of receptor mRNA occur in heart and major vessels. Postnatally transcription is strongly down-regulated. This suggests a role for the IGF-II/M-6-P receptor in IGF-II action or turnover during development distinct from its role in lysosomal transport.