Insulin-like growth factor mRNA in barramundi (Lates calcarifer): Alternative splicing and nonresponsiveness to growth hormone

Barramundi (Lates calcarifer) is a teleost of the superorder Acanthopterygi i. Barramundi IGF-I cDNA was cloned and the distribution of alternative tra nscripts in various barramundi tissues was investigated using rt-PCR and RP A. It was demonstrated that in barramundi tissues, IGF-I mRNAs were represe nted by two transcripts corresponding to the reported salmonid Ea-2 and Ea- 4. The acute effect of GH on hepatic IGF-I mRNA levels was investigated. Se ven hours after intraperitonal administration of either 6 mu g of recombina nt bream GH/g body weight or saline, no significant increase in the levels of either of the two transcripts could be observed. The presence of GH rece ptors in the barramundi liver was demonstrated in binding assays using reco mbinant bream GH and liver membrane preparations. An analysis of a barramun di IGF-I genomic sequence encompassing the three exons that encode the E do main suggested that the pattern of splice site utilization is determined by the degree of homology of the splicing signals to the consensus splice sit e sequences.