Agro-Biotechnology: - The Greens | European Free Alliance

Technical problems | Cloned farm animals - a ‚killing application‘? | 15
2.2 Epigenetics and underlying causes of adverse
health impacts
In the opinion of EFSA (2008a), FDA (2008) and the report by Gjerries & Vatja
(2005), the role of epigenetics is emphasised. Epigenetics is a biological mechanism
occurring in all mammals and plants. In recent years, there has been
considerable progress in the identification and detailed understanding of the
molecular mechanisms underlying epigenetic inheritance. In general epigenetic
mechanisms can be described as alterations of gene expression by biochemical
modifications (such as methylation of the DNA or DNA-binding proteins). The
process does not involve changes in the DNA sequence, but can be transmitted
to following generations.
Several epigenetic mechanisms are involved in regulation of the genome
during embryonic development, growth and reproduction. These factors can be
substantially disturbed by the process of reprogramming. It is due to these systemic
effects that the causes of adverse impact of SCNT on animal health have
not yet been able to be determined in detail and no precise predictions can be
made about their consequences. This gives rise to a high level of uncertainty
about adverse health effects in cloned animals and the food derived from them.
A report commissioned by the Netherlands Commission on Genetic Modification
(COGEM) explains some of the molecular mechanisms shaping the epigenome
of higher organisms (Nap & van Kessel, 2006). These mechanisms can
be described by defined biochemical reactions, but their impact can hardly be
predicted, since they are directed not at specific genetic information but by the
impact of the genome regulation on a general level.
Nap & van Kessel describe four different levels of epigenetic mechanisms:
• DNA methylation (and demethylation)
• Protein (notably histone) modification
• RNA-based mechanisms
• Higher order chromatin-based mechanisms
Nap & van Kessel describe the reprogramming in SCNT as highly problematic
and more or less unpredictable in its outcome:
“In contrast, reprogramming for cloning in mammals is problematic. Both the
erasure of the epigenetic memory of the differentiated donor cells and the
establishment of the epigenetic program of the early embryo appear highly
defective in most cloned embryos. Epigenetic reprogramming during cloning
is apparently a stochastic process, the outcome of which is difficult, if not
impossible, to predict.“
According to Gjerries & Vatja (2005) the effects observed are highly dependent
on several circumstances and have to be assessed in each and every case.
They differ from species to species and are influenced by the source of the donor
cell and the quality of the recipient cell. But the 'craftsmanship' (experience