Characterization of the insulin-like growth factor type 1 receptor messenger in two teleost species

The insulin-like growth factor type 1 receptor (IGF-1R) is a tyrosine kinase which plays essential role in the regulation of growth and development. In this study, we have cloned cDNAs encoding the tyrosine kinase domain of the IGF-1R from two species of fish. The turbot and trout nucleotide sequences share 82% identity. Moreover, the deduced polypeptides are also highly conserved (> 90% identity) compared with the IGF-1R sequences described in other vertebrates, particularly within domains involved in the catalytic activity and in the transduction pathway. Northern blot analyses have revealed a unique 13-kb mRNA transcript. Using an RT-PCR approach, we have also shown that the polyadenylation status seems to vary according to the developmental stage in turbot: polyadenylated in oocytes and in the first larval stages, the mRNA becomes undetectable in the polyadenylated fraction in later stages or in adult somatic tissues. These results suggest that IGF-1R mRNA undergoes complex post-transcriptional regulation.