Growth hormone receptors in the atherinid Odontesthes bonariensis: characterization and expression profile after fasting-refeeding and growth hormone administration.

In order to improve the understanding of pejerrey Odontesthes bonariensis, growth hormone (Gh)-insulin-like growth factor-1(Igf1) axis, O. bonariensis growth hormone receptor type 1 (ghr1) and type 2 (ghr2) mRNA sequences were obtained. Both transcripts were ubiquitously expressed except in kidney, encephalon and anterior intestine. Alternative transcripts of both receptors were found in muscle. Interestingly, two different ghr2 transcripts with alternative polyadenylation (APA) sites located in the long 3' untranslated region (UTR-APA) were also found in liver. Hepatic ghr1, ghr2 and insulin-like growth factor type 1 (igf1) transcript levels were examined under two different metabolic conditions. In the first experimental condition, fish were fasted for 2 weeks and then re-fed for another 2 weeks. Despite igf1 mRNA relative expression did not show significant differences under the experimental period of time examined, both ghr transcripts decreased their expression levels after the fasting period and returned to their control levels after re-feeding. In the second treatment, recombinant O. bonariensis growth hormone (r-pjGh) was orally administered once a week. After 4 weeks of treatment, liver igf1, ghr1 and ghr2 mRNA relative expression increased (13, 4·5 and 2·1 fold, P < 0·05) compared to control values. These results add novel information to the growth hormone-insulin-like growth factor system in teleosts.

Molecular cloning, expression and immunological characterization of pejerrey (Odontesthes bonariensis) growth hormone.

Growth hormone is an essential polypeptide required for normal growth and development of vertebrates. The pejerrey fish, Odontesthes bonariensis, is a South American atherinid freshwater fish considered as a promising species for aquaculture. Although growth hormone has been characterized in a number of fish, there are no published data on the structure of this hormone in atherinids, except that of a related species Odontesthes argentinensis. In this paper, the molecular cloning, expression and immunological characterization of pejerrey growth hormone (pjGH) is described. The predicted amino acid sequence of pjGH cDNA consisted of 204 amino acid residues with an estimated molecular mass of 23 kDa. Amino acid sequence was highly conserved among the two Atheriniformes where the growth hormone sequences are known (99% aa identity), highly to moderately conserve (75-92% aa identity) when compared to the other members of Acantopterigii superorder and clearly less conserved (49-66% identity) when compared to Salmoniformes (Protacanthopterygii), Cypriniformes and Siluriformes (Ostariophysi). A phylogenetic tree depicting the relationship of various teleost GH nucleotide sequences was inferred. Pejerrey GH was produced using recombinant DNA technology in a bacterial system, representing the first time an atherinid growth hormone protein was expressed as a recombinant protein in Escherichia coli. A specific antiserum of this hormone was raised in rabbits and its specificity tested by using Western blot and immunocytochemistry. The distribution of pjGH mRNA was also studied by RT-PCR and Southern blot analysis. The transcript was detected not only in the pituitary gland but also in the testis.