Characterization of teleost insulin receptor family members. II. Developmental expression of insulin-like growth factor type I receptor messenger RNAs in rainbow trout.
The insulin-like growth factor (IGF) system in teleosts consists of two ligands, IGF-I and IGF-II, multiple binding proteins, and high-affinity transmembrane receptors. There exists a large gap in our knowledge of the structure and expression of receptors mediating the biological effects of the IGFs in teleosts. For example, nucleotide sequence data other than those from the kinase domain, evidence of multiple genes, mRNA expression pattern and polyadenylation status in multiple tissues at different developmental stages, and quantitation of mRNA levels in multiple tissues are not known for any teleost. In the study described here, two rainbow trout IGF type I receptor cDNAs (rtIGFR Ia and rtIGFR Ib) were isolated by a 5' rapid amplification of cDNA ends method and confirmed as separate genes by genomic Southern blot hybridization. The predicted amino acid sequences are 85% identical to each other in the tyrosine kinase domain. Both cDNAs are more homologous to mammalian IGF type I receptors than to insulin receptors. Reverse transcription-polymerase chain reaction from total RNA using either oligo(dT) or random hexamers as primers resulted in a diminished ability to detect IGF receptor mRNAs when oligo(dT) was used, suggesting developmental and tissue-specific polyadenylation. The highest steady-state mRNA levels of rtIGFR Ia were found in juvenile gill and adult heart, while the highest levels of rtIGFR Ib were found in adult pyloric caeca, which also contained diffuse pancreatic and adipose tissue. The lowest steady-state mRNA levels of both rtIGFR Ia and rtIGFR Ib were found in juvenile heart, liver, muscle, and spleen, and adult liver. Significant differences in steady-state mRNA levels were also found between juveniles and adults. These results suggest a complex expression pattern of IGF type I receptor mRNAs in partial tetraploid fish.
Biotechnology Center, University of Connecticut, Storrs, Connecticut 06269, USA.
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015139:Blotting, Southern; D003001:Cloning, Molecular; D017124:Conserved Sequence; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism; D008969:Molecular Sequence Data; D017686:Oncorhynchus mykiss / Q000254:growth & development / Q000378:metabolism*; D011061:Poly A / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D012333:RNA, Messenger; D011061:Poly A; D007334:Insulin-Like Growth Factor I