The GH (growth hormone) cDNA sequence of the marine silverside fish Odontesthes argentinensis was obtained using the RACE protocol (Rapid Amplification of cDNA Ends). The marine silverside GH cDNA sequence is 928 nucleotides long and was found to encode a polypeptide of 204 amino acids, including a signal peptide of 17 amino acids. The 5' and 3' untranslated regions of the messenger are 109 and 204 nucleotides long, respectively. The deduced GH amino acid sequence was used to infer a phylogenetic tree with GH amino acid sequences from representative species belonging to the Euteleostei Subdivision using the maximum parsimony method. The topology found is according to the major phylogenetic grouping of euteleosts. The results corroborate the hypothesis that atherinids are not related to paracanthopterygians as previously suggested, and show a lack of solid synapomorphies among most of the Acanthopterygii Orders analysed indicating a complex assemblage of fishes in which the phylogenetic tree remains indeterminable.

In this study, we describe the use of a STAT5 responsive element (LHRE) reporter gene to monitor the activity of the growth hormone (GH) transduction pathway following expression of heterologous fish GH and rat STAT5b in tilapia embryos and fish fibroblast cells. Our results indicate that both GH and STAT5b are able to activate the LHRE at high levels when transferred separately, demonstrating the substantial level of conservation of the GH signal transduction pathways between fish and mammals. Unexpectedly, co-expression experiments show a strong inhibition of the GH-dependent activation, suggesting that simultaneous GH and STAT5b overexpression can counteract effects of GH expression in tilapia embryos.