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Cloned BSE-Free Cows, Not Safe Nor Proper Science

Thursday, February 1, 2007
Posted in Genetic Engineering | Tagged Genetic Engineering

Dr. Mae-Wan Ho and Prof. Joe Cummins go behind the
smokescreen to expose the project which would perpetuate the
intensive animal husbandry that created mad cow disease in
the first place and is far from safe or ethical in terms of
animal welfare

An orchestrated regulatory road show
************************************

Scientists announced the successful creation of cloned cows
that would not get infected by BSE (Bovine Spongiform
Encephalitis) [1], the dreaded mad cow disease that
devastated the beef industry in Britain more than 20 years
ago [2] ( The Inside Story of BSE , SiS 32). In potential
re-enactment of the BSE fiasco, government regulators, in
this case, the United States Food and Drug Administration
(FDA), is about to approve cloned meat and milk for sale,
pronouncing them safe despite massive public opposition on
both safety and ethical grounds [3] ( Is FDA Promoting or
Regulating Cloned Meat and Milk? this series). Meanwhile,
Codex Alimentarius, the United Nations’ food standards
agency, has put out a public consultation on transgenic food
animals that are likely to be contaminated with dangerous
vaccines, drugs and nucleic acids [4] ( GM Food Animals
Coming , SiS 32). Is this a coincidence or a well-
orchestrated regulatory road show to smooth the passage of
cloned transgenic animals into the world market?

Cloning by somatic cell nuclear transfer (SCNT) is the key
to propagating genetically modified (GM) animals, as they do
not breed true, the transgene is either silenced or
physically lost in subsequent generations. Dolly the cloned
sheep was the first mammal to be created by SCNT, and
although not herself transgenic, she was followed by an
entire herd of cloned transgenic sheep producing human
alpha-1 antitrypsin in milk. Unfortunately, Dolly had to be
put down in 2002 at age six, and the transgenic herd
destroyed a year later; the process proved neither
technically efficient nor financially viable [3]. The
scientists involved, including Ian Wilmut the creator of
Dolly, abandoned cloning livestock to concentrate their
efforts into using SCNT to make human embryonic stem cells
for research and tissue replacement. But others have
obviously not given up.

Precise gene targeting claimed
******************************

The cloned cows that would not get infected by BSE was
created by precise ‘gene targeting’, which on the face of
it, looked far more advanced than the conventional genetic
modification that is highly unpredictable and
uncontrollable, resulting in a great deal of mutations, DNA
scrambling and other collateral damage to the host genome
[5] ( FAQ on Genetic Engineering , ISIS tutorial) . Instead,
gene targeting involves, in theory at least, a precise
‘knockout’ of the gene coding for the offending prion
protein responsible for BSE. And that may become the selling
point for both cloned and transgenic animals.

Normal proteins that cause disease by misfolding
************************************************

Prion proteins occur normally in a harmless form. But by
folding into an aberrant shape, the normal prion protein
turns into a rogue, infectious agent that is able to convert
other normal prion protein molecules to fold into the same
aberrant shape [6-8] ( Living Test for Mad Cow Disease , SiS
28). Prions are thought to be responsible for a number of
degenerative brain diseases, including scrapie (a fatal
disease of sheep and goats), BSE in cows, a chronic wasting
disease in deer and elk, Creutzfeldt-Jakob disease (CJD) and
its variant, vCJD, fatal familial insomnia, kuru (a slowly
progressing fatal brain disease in Papua New Guinea),
Gertsmann-Straeussler-Scheinker disease (an unusual form of
hereditary dementia), and possibly some cases of Alzheimer’s
disease.

Normal prion protein is encoded by a gene in mammals, and is
found throughout the body, even in healthy people and
animals. However, the prion protein in infectious material
has a different structure and is resistant to proteases (the
enzymes in the body that break down proteins ) as well as to
heat, radiation and formaldehye, treatments that would
normally have killed viruses, bacteria and other disease
agents.

Gene knockout in mice
*********************

Transgenic cloned mice with both copies of the prion gene
disrupted (knockout) by homologous recombination showed no
gross abnormalities, and neither produced prions nor
harboured prion infection. However, deletions of the prion
gene that extended into flanking genes caused the knockout
mice to suffer ataxia (shaky, unsteady movement) and
Purkinje cell loss in the adults [9]. One study found that
mice devoid of prion protein had cognitive deficits that
could be rescued by reconstitution of prion genes in neurons
[10].

Sheep cell lines with both copies of the prion protein gene
knocked out were used to clone lambs by SCNT. The four lambs
born live soon succumbed, three at birth and one after 12
days [11].

Gene knockout by homologous recombination has been used
extensively for gene function analysis in mice, where it is
accomplished using embryonic stem (ES) cells that can be
made to develop into transgenic mice after genetic
modification. In all other species, ES cells suitable for
gene targeting are not available, and somatic cells have to
be used. The genetically modified cells are then cloned into
embryos by SCNT, and the embryos used to produce cloned
offspring.

Gene targeting of somatic cells has the disadvantage that
somatic cells have a short lifespan, which limits selection
of properly targeted cell colonies and a low frequency of
homologous recombination compared with embryonic stem cells.

To get the full consequence of a genetic knockout, both
copies of the gene must be disrupted. In mice, heterozygous
knockout founders are bred to produce a homozygous (both
copies of the gene identical) inbred line. This takes a long
time in species with long generation times, and the animals
generally suffer from consequences of inbreeding, resulting
in defective or otherwise weak animals.

Read the rest of this article here
http://www.i-sis.org.uk/Cloned_BSE-Free_Cows.php

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This article can be found on the I-SIS website at
http://www.i-sis.org.uk/

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dedicated to providing critical public information on
cutting edge science, and to promoting social accountability
and ecological sustainability in science.