Production of Recombinant Hormones and Growth Factors for Use in Aquaculture

Extended Abstract Progress in recombinant DNA technology and development of new expression systems has provided valuable means to produce large quantities of hormones and growth factors from various fish species that otherwise required sacrifice of enormous numbers of fish to obtain only small amounts of the native protein. The motivation to produce recombinant hormones and growth factors for application to fish culture can be attributed to (a) the low amounts of peptides in producing tissues available for purification and characterization by classical methods, i.e., follicle stimulating hormone (FSH = GtH-I) in the pituitary or insulin-like growth factor-I (IGF-I) and IGF-II in the liver, (b) the similarity in chemical structure between two hormones that does not permit efficient separation (FSH and LH = GtH-II), (c) the need for large quantities of hormones for growth enhancement by growth hormone (GH), and (d) interest in studying structure/function relationships, i.e., single or multiple amino acid deletion, amino acid substitution, etc. The first two recombinant fish GHs were produced twenty years ago from salmon and rainbow trout. Since then, numerous fish GH peptides have been produced from a variety of species, most of them cultured fish species (for a partial list see Funkenstein, 2000, which covers only those reported until 1999). New species are constantly being added to this list as additional GH cDNAs are cloned from fish. In contrast to the increasing number of recombinant fish GHs produced so far, relatively few studies describe the production of fish recombinant IGFs (Funkenstein, 2000). Yet, the need for fish IGF-I and IGF-II, mainly for developing homologous, or at least of fish origin, quantitative assays has prompted the production of additional IGFs. The shortage of fish IGFs provided the incentive to the Australian company GroPep (www.gropep. com.au) to undertake production of recombinant fish GHs and IGFs from a variety of cultured fish species. In general, production of recombinant proteins involves cloning of cDNA coding for the desired peptides in appropriate expression vectors. The choice of vectors depends on the expression system employed. An important consideration in the choice of vector and system depends on characteristics of the peptide in question such as post-translational modifications (glycosylation) or formation of