GMO food from transgenic animals?
Lech Zwierzchowski
Institute of Genetics and Animal Breeding PAS, Jastrzębiec, 05-552 Wólka Kosowska,
Poland
The improvement of animal production by transgenesis is expected to be
complementary to other breeding techniques, including genetic selection. Projects are in
progress to use transgenic animals both in agriculture and in medicine. Insertion of transgenes
and other gene manipulations can improve production traits in farm animals. The most
important targets for animal transgenesis are: (1) animal growth rate and meat production;
(2) milk yield and milk quality; (3) wool production and quality; (4) resistance to diseases;
(5) better or controlled reproduction; (6) digestion of normally nondigestable feeds or
antinutrients, eg. phytic acid (less phosphate released to environment). Animal transgenesis is
also a great hope for human medicine. Transgenic animals are excellent models for human
diseases. Genetically manipulated farm animals will serve as producers of human
pharmaceuticals – live bioreactors producing human protein medicines in milk, blood, eggs,
or urine. Transgenic animals, mostly pigs will be donors of organs for xenotransplantntion.
In this paper the present state of animal transgenesis is reviewed, in particular the
potential of using transgenic animals as a source of food for humans. Production of
biopharmaceuticals in mammary gland of transgenic animals is now a reality. Recombinant
human therapeutical proteins purified from milk of transgenic animals will soon appear in
pharmacies. Several human biopharmaceuticals, eg. -1-atitrypsin, antitrombin or
glucosidase are now produced in amounts sufficient for commercial use and passed all
necessary clinical trials; now they await FDA acceptance. Other modifications of milk
composition were made on mice, the only animal for which totipotential embryonic stem cells
(ESC) are available. Modification of composition of ruminants milk is a long distance target;
new techniques of gene manipulations in farm animals, such as gene targeting, homologous
recombination, gene knock-out, must be developed and refined before such modifications will
be a reality.
Attempts to use gene manipulation for increasing growth rate and meat production was
a disappointment. Transgenic rabbits with human GHRH gene fused to mMT promoter
obtained in our laboratory grew faster during first several weeks of life and at the age of 5
weeks were on average 30% heavier then controls (Rosochacki et al., 1992). But rabbit is of
the minor importance as a meat animal, especially in Poland. In different laboratories
transgenic pigs were obtained overexpressing growth hormone from gene constructs with
human, bovie, or porcine sequences (Pursel et al., 1990). Some of them grew slightly faster,
better converted feed, and were leaner then their non-transgenic siblings. However, they
suffered from stomach ulcers, arthritis, and other disorders. Attempts to use transgenesis to
increase growth of other farm animals – cattle, sheep - completely failed. The only exception
is transgenic fish. Our transgenic carps with human GH gene expressed under direction of X.
laevis -actin gene promoter were at the age of 1 year on average 40% heavier and 6 cm
longer then the non-transgenics (Rosochacki et al., 1993). Transgenic salmons obtained by
Devlin et al., (1994) and Do et al., (1992) were on average 11 times heavier then controls and
some of them reached the body weight almost 35 times higher. Now, fast-growing
commercial fish - salmon, carp, tilapia - endowed with all-fish GH gene constructs are
produced and will soon appear on the food market; they only need agreements from relevant
commissions and of course a public acceptance. Using methods of gene manipulation to
increase wool growth and quality or to endow animals with disease resistance as so far is of
minor importance for animal breeding and food production and need further technical
improvement.
Genetic manipulation of animals for food production is not only a technical problem.
Public acceptance of such manipulations is necessary and safety of GMO food must be
considered. It must be stressed, however, that as so far no products derived from transgenic
animals, either medicine or food, are available on the market. But this situation will possibly
change soon.
References
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