Regulation of somatic growth and gene expression of the GH–IGF system and PRP-PACAP by dietary lipid level in early juveniles of a teleost fish, the pejerrey (Odontesthes bonariensis)

Abstract

Growth and mRNA levels of the pituitaryadenylate cyclase-activating polypeptide (PACAP) and itsrelated peptide (PRP), and the system controlled by thegrowth hormone (GH) and insulin-like growth factors(IGFs) were analyzed in pejerrey fry fed with graded levelsof dietary lipids: 10% (L10), 13% (L13) and 21% (L21).First, the full sequence of pejerrey PRP-PACAP wasobtained by RT-PCR, using primers based on conservedfragments of teleosts PACAP sequences. The growth of thefish at 83 days after hatching (dah) and the GH mRNAlevels were not significantly affected by the dietary treatment.Conversely, PRP-PACAP expression significantlydecreased with increasing dietary lipids (L10[L21).While GH receptor (GHR)-I and IGF-I transcripts did notdiffer among groups, GHR-II transcripts decreased ingroup L21. IGF-II expression apparently followed thesame trend. These results in combination with the lowerexpression of the anorexigenic PRP-PACAP in fish fed dietL21 and the correlation analysis evidencing a particularlyfine tuning of the GH?IGF system in group L13, suggestthat this diet may cover the energy demands for growingpejerrey from 27 dah onwards. Our results show for firsttime in fish a differential response of PRP-PACAP transcriptsto dietary manipulations, and confirm the sensitivityof the pejerrey GH?IGF system to changes in dietcomposition despite the lack of (or in advance to) a clearresponse of somatic growth.