1.1 Biotechnological applications of animals, plants, and microbes
In transgenic biotechnology (also known as genetic engineering), a known gene is inserted into an animal, plant, or microbial cell in order to achieve a desired trait. Biotechnology involves the potential use of all living forms, but microorganisms have played a major role in the development of biotechnology. This is because of the following reasons: (i) mass growth of microorganisms is possible, (ii) cheap waste materials which act as the media for the growth of microorganisms can be rapidly grown, and (iii) there is massive diversity in the metabolic types, which in turn gives diverse potential products and results in the ease of genetic manipulation to improve strains for new products. However, mass culture of animal cell lines is also important to manufacture viral vaccines and other products of biotechnology. Currently, recombinant DNA (rDNA) products produced in animal cell cultures include enzymes, synthetic hormones, immunobiologicals (monoclonal antibodies, interleukins (ILs), lymphokines), and anticancer agents. Although many simpler proteins can be produced by recombinant bacterial cell cultures, more complex proteins that are glycosylated (carbohydrate-modified) currently must be made in animal cells. However, the cost of growing mammalian cell cultures is high, and thus research is underway to produce such complex proteins in insect cells or in higher plants. Single embryonic cell and somatic embryos are used as a source for direct gene transfer via particle bombardment, and analyze transit gene expression. Mammarian cell-line products (expressed by CHO, BHK (baby hamster kidney), NSO, meyloma cells, C127, HEK293) account for over 70% of the products in the biopharmaceutical markets including therapeutic monoclonal antibodies.
Biopharmaceuticals may be produced from microbial cells (e.g., recombinant Escherichia coli or yeast cultures), mammalian cell culture, plant cell/tissue culture, and moss plants in bioreactors of various configurations, including photo-bioreactors. The important issues of cell culture are cost of production (a low-volume, high-purity product is desirable) and microbial contamination by bacteria, viruses, mycoplasma, and so on. Alternative but potentially controversial platforms of production that are being tested include whole plants and animals. The production of these organisms represents a significant risk in terms of investment and the risk of nonacceptance by government bodies due to safety and ethical issues.
The important animal cell culture products are monoclonal antibodies; it is possible for these antibodies to fuse normal cells with an immortalized tumor cell line. In brief, lymphocytes isolated from the spleen (or possibly blood) of an immunized animal are fused with an immortal myeloma cell line (B cell lineage) to produce a hybridoma, which has the antibody specificity of the primary lymphoctye and the immortality of the myeloma. Selective growth medium (hyaluronic acid (HA) or hypoxanthineâaminopterinâthymidine (HAT)) is used to select against unfused myeloma cells; primary lymphoctyes die quickly during culture but only the fused cells survive. These are screened for production of the required antibody, generally in pools to start with and then after single cloning, the protein is purified. As mammals are also a good bioreactor to secrete the fully active proteins in milk, several species since 1985 have been cloned including cow, goat, pig, horse, cat, and most recently dog, but the most research has been on cloning of cattle. Genetically modified (GM) pigs, sheep, cattle, goats, rabbits, chickens, and fish have all been reported.
The main potential commercial applications of cloned and GM animals include production of food, pharmaceuticals (âpharmingâ), xenotransplantation, pets, sporting animals and endangered species. GM animals already on sale include cloned pet cats, GM ornamental fish, cloned horses, and at least one rodeo bull. Two pharmaceutical products from the milk of GM animals have completed (Phase III and Phase II) clinical trials, respectively, and may be on the market in the EU in the next few years. Cloned livestock (especially pigs and cattle) are widely expected to be used within the food chain somewhere in the world, though it would not be economical to use cloned animals directly for food or milk production, but clones would be used as parents of slaughter pigs, beef cattle, and possibly also milk-producing dairy cows. The first drug manufactured from the milk of a GM goat was ATryn (brand name of the anticoagulant antithrombin) by GTC Biotherapeutics in 2006. It is produced from the milk of goats that have been GM to produce human antithrombin. A goat that produces spider's web protein, which is stronger and more flexible than steel (BioSteel), was successfully produced by a Quebec-based Canadian company, Nixia.
Faster-growing GM salmon developed by a Canadian company is also awaiting regulatory approval, principally for direct sale to fish farming markets. Canada has also approved the GM pig (trade named âEnviropigâ) developed by University of Guelph and it is designed to reduce phosphorus pollution of water and farmers' feed costs. Enviropig excretes less phosphorous manure and is a more environmentally friendly pig. It will be years before meat from genetically engineered pigs could be available for human consumption. Molecular pharming can also produce a range of proteins produced from cloned cattle, goats, and chickens. An ornamental fish that glows in the dark is now available in the market. It was created by cloning the deoxyribonucleic acid (DNA) of jellyfish with that of a zebra fish. GM fish may escape and damage the current ecosystem by colonizing waters. Some tropical fish, like piranhas, could be engineered to survive in the cold and this could lead to major problems. These details will be covered in the section on Animal Biotechnology.
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