Business Potential for Agricultural Biotechnology - Asian Productivity ...

Business Potential for Agricultural Biotechnology Products
considered as an antibacterial agent against some fish pathogens, including Aeromonas salmonicida,
which causes furunculosis in rainbow trout (Siwicki et al., 1998). In fish the lysozyme
cDNA have already been cloned from rainbow trout and Japanese flounder (Hikima et al., 2001).
Another approach is to induce fish to express some antimicrobial peptides, for example, pleurocidin
and moronecidin (Douglas et al., 2001; Lauth et al., 2002). The antimicrobial peptide
monodoncin, which consists of 55 amino acid residues, was isolated from the haemocyte of
black tiger shrimp (Penaeus monodon) and showed efficient antimicrobial ability against some
aquatic pathogens such as Aerococcus viridans, Fusarium pisi, and Fusarium oxysporum (Chen
et al., 2005; Chio et al., 2005). On the other hand, a liposome-based gene transfer platform was
developed to transfer useful genes into silver sea bream (Sparus sarba) (Lu et al., 2002).
Many species of polar fish secrete antifreeze proteins (AFPs) into their plasma to avoid
freezing. Diverse types of antifreeze proteins have been characterized and cloned from a variety
of fish, including winter flounder (Pleuronectes americanus) and ocean pout (Macrozoarces
americanus). These proteins have the unique property of inhibiting ice crystal growth by binding
to the ice surface and lowering the freezing temperature. Therefore, introducing an AFP gene
would generate a freeze-tolerant transgenic fish. The enzyme creatine kinase plays a key role in
the energy metabolism of cells that have fluctuating energy requirements. Three forms of
creatine kinase (CK) muscle isoenzyme cDNAs were isolated from carp (Cyprinus carpio). M3-
CK was found to be the major regulatory enzyme of energy metabolism, and cold tolerance was
improved in transgenic zebrafish. It is expected that the application of CK would decrease losses
in the aquaculture industry in cold waters.
Infertile Technology for Genetically Modified Fish
Commercial production of transgenic fish will depend on the risk posed to wild species.
Although useful transgenic fish strains have been developed, so far they have not been generally
used in aquaculture because of concerns that genetically modified fish may threaten natural ecosystems.
If these genetically modified fish escaped and bred with their wild type, the consequences
of spreading the modified gene into the environment are unpredictable (Reichhardt,
2000). Therefore, genetically modified fish for human consumption should be made sterile.
Experiments will have to be conducted on transgenic fish survivability and infertility, not only in
the laboratory but also in natural conditions. The common practices to produce sterile fish are
heat-shock or pressure-shock treatment of the freshly fertilized fish eggs, treatment of females
with male sex hormones, and polyploid infertile technology, but the methods are not 100%
effective (Razak et al., 1999). Gonadotropin-releasing hormone (GnRH) is a decapeptide which
regulates synthesis and release of follicle-stimulating hormone (FSH) and luteinizing hormone
(LH) and thereby plays a primary role in the control of reproductive function in vertebrates.
Therefore, an alternative method could produce induced sterility in transgenic lines by blocking
the gonadotropin-releasing hormone (GnRH) with antisense RNA. A report has shown that
deletion of the GAP region of the GnRH gene decreased the level of gonadotropin in mice, resulting
in complete sterility (Mason et al., 1996). In fish, GnRH is thought to play an important
role in sexual maturation and reproductive behavior, and two or three forms of GnRH peptide
have been identified. Three forms of GnRH cDNA, seabream form (sbGnRH), chicken type II
form (cGnRH-II), and salmon form (sGnRH) have been cloned from Sparus saeba, and the promoter
regions were cloned by genome walking. Estrogen responsive element (ERE) and progesterone
responsive element (PRE), which are involved in the modulation of estrogen and progesterone
and the expression of vitellogenin gene, were found in these promoter regions. Depending
on promoter structure and regulatory function of three forms of GnRH, the expression of gonadotropin
(GTH) gene would be down-regulation in the pituitary gland to cause gonad undevelopment
by using the specific and inducible promoter to drive the expression of antisense RNA or
cell apoptotic gene such as the bax and bok gene. The establishment of infertile technology may
lead to genetically modified fish being unable to spawn in the wild during the next generation.
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