Tilapia somatotropin polypeptides: potent enhancers of fish growth and innate immunity

Growth hormone (GH) is a single chain polypeptide of approximately 22 kDa, produced by the pituitary gland and with pleiotropic functions among vertebrates. It mainly regulates body growth, being also involved in reproduction, immunity and osmoregulation in teleost fish. In order to obtain the tilapia (Oreochromis hornorum) growth hormone (tiGH) in Pichia pastoris cells, its gene was cloned into expression vectors in both with and without a heterologous secretion signal. The tiGH, obtained either intracellularly or extracellularly in P. pastoris cells, was characterized showing its production as associated to the cellular rupture precipitate with an approximate molecular weight of 22 kDa; or being secreted with an approximate molecular weight of 18 kDa, respectively. The mass spectrometry analysis of the recombinant protein obtained in the culture supernatant corroborated the identity of the protein as tiGH but lacking 46 aminoacids of its carboxyl terminal sequence. The tiGH biological activity of P. pastoris intact cells producing this protein was carried out in tilapia larvae (Oreochromis sp.), showing, for the first time, that it is possible to stimulate fish growth by immersion baths with recombinant tiGH-producing yeast. On the contrary what was previously postulated for mammals, the evaluation of P. pastoris cells expressing the truncated variant of tiGH demonstrated that this protein is also able to stimulate growth and immune system in fish. This is the first report of a biologically active, truncated GH variant in fish.