Animal and Plant Improvement
Transgenic Farm Animals
Production of transgenic animals through microinjection techniques will play a significant role in veterinary sciences as well as for human welfare. A farm animal can produce milk containing tens of gram of protein per liter, many times more than a liter of bacterial culture. The possibility of producing human pharmaceutical demonstrated when lactating mice secreted the active tissue plasminogen activator (t-PA) in their milk. The t-PA is an enzymes which dissolves the blood clots responsible for coronary artery blockage that results in heart failure. John Me Pherson at Genzyme Co., in collaboration with K. Elbert and colleagues of Tuft University produced the first transgenic goat by using a goat beta-casein promoter gene linked to t-PA gene. The transgenic goat produced t-PA in quantities as compared to cell culture derived material. But goat peptide is slightly different from the culture derived t-PA. The goat peptide has two chains of peptide, whereas a single chain peptide was found in culture derived t-PA. Therefore, much work is needed in future.
Recently, Pharmaceutical Proteins Ltd. has made contract with Bayer Co. (Germany) to produce alpha-1 antitrypsin by using transgenic sheep. Alpha-1 antitrypsin, a glycoprotein, has now been approved in the U.S.A. as a replacement therapy. The scientists are of the opinion that about 12 kg sheep/lactation alpha-1 antitrypsin can be produced.
Production of transgenic cow has also been demonstrated in the Netherlands but unsuccessful. The eggs of cow collected from ovaries from slaughter houses were fertilized in vitro
and microinjected with transgenes containing lactiferous gene. The embryos were implanted in the uterus of surrogate mothers. Out of 102 injected embryos, 21 animals were pregnant and 10 calves were borne. Two of these, one male and the other female, carried transgene. The male showed the presence of lactoferrin gene but not the female. A male never gives out milk. Till the animal secretes milk, the experiment is incomplete. But this experiment has given a hope for future.
Caseins are the major proteins of the milk. By transferring genetically manipulated casein genes to farm animals, the texture of cheese and heat stable dairy products can be improved. Casein genes have already been cloned and introduced into bovine genome.
Recently, T.J. Pandian and colleagues of Madurai Kamraj University have succeed in producing transgenic fishes by microinjecting growth hormone gene (human or bovine). A fish produces a large number of eggs at a time. It is much easier to work on eggs for gene manipulation. In developing countries like India, where majority of people suffer from malnutrition, the aquaculture programmes can be intensified for production on a large scale of good quality fishes.