Fwd: New GM Toxin Looms over Our Food

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Tue, 2 Dec 2003 15:55:23 GMT

 

New GM Toxin Looms over Our Food

press-release

 

The Institute of Science in Society

Science Society Sustainability

http://www.i-sis.org.uk

 

General Enquiries sam

Website/Mailing List press-release

ISIS Director m.w.ho

===================================================

 

ISIS Press Release 02/12/03

New GM Toxin Looms over Our Food

********************************

Prof. Joe Cummins issues advance warning of new GM toxin from soil bacterium

that’s to be incorporated into our food crops.

 

Sources (http://www.i-sis.org.uk/full/NGMTLOOFFull.php) for this report are

available in the ISIS members site. Full details here

(http://www.i-sis.org.uk/membership.php)

 

The soil bacterium, Bacillus thuringiensis (Bt), has proven to be a rich source

of toxins for killing insect pests. Most of the toxin genes now being used in

genetically modified (GM) crops are produced in sporulating Bt, and belong to

the Cry family: designated Cry1, Cry 2 etc. up to at least Cry 41. The Cry genes

are further distinguished as Cry1A, Cry1B etc for substantial sequence

variations, and labeled Cry1Aa, Cry1Ab etc for very small differences in

sequence. The Cry gene toxins target specific insect cell receptor proteins and

create pores that lead to osmotic lysis of the insect gut cells. Only a few Cry

genes have found favour in GM crops. Along with the Cry genes, Cyt genes have

been characterized that are distinct from Cry genes and act by breaking open the

insect’s blood cells.

 

In recent years, vegetative insecticidal proteins (VIP) have been found to have

potent, broad-spectrum activity against insects. VIP genes are not homologous to

Cry and Cyt genes, and bind to cell membrane proteins different from the other

toxins.

 

Syngenta Corporation, producers of chemical and biological pesticides, has

patented the VIP genes for use in transgenic crop plants and microbes.

Syngenta’s United States patent 6 429 360 covers the use of Bt-VIP genes and

their synthesis and alteration to improve performance in crop plants. Syngenta’s

patent provided evidence that VIP3A toxin produced apoptotic type of cell death,

including the production of membrane-bound apoptotic bodies and activation of

endonuclease enzymes that cleave chromatin into discrete fragments.

 

Apoptosis (meaning petals falling from a flower) is a form of programmed cell

death common to all cells with discrete nuclei. It is a part of normal

development, but the VIP3A toxin uses programmed cell death to destroy the cells

of the insect gut. In order to function fully in the plant cells, the Bt-VIP3A

gene is modified in its coding sequence; a strong promoter added, as well as an

intron to facilitate transfer of the pre-messenger RNA from nucleus to

cytoplasm; and the usual transcription terminator and polyA addition sequences.

 

The insect VIP3A receptor was identified and its characteristic " death "

recognition sequence was characterized. Organisms whose cells have nuclei

generally have receptors with death signals and the insect VIP3A receptor is a

unique member of the class of sequences.

 

Syngenta has petitioned the United States Environmental protection Agency (EPA)

for commercial release of event COT102 cotton containing a synthetic VIPA3 gene.

Presumably, corn containing the VIP3A gene will be proposed for commercial

release. The EPA report of the Syngenta petition for tolerance in or near food

reported that the VIPA3 toxin was homologous to the VIP3A toxin in numerous Bt

strains. However, the petition failed to mention the numerous change in DNA

sequence including promoter, introns, terminator and polyA signal, which were

reported in the Syngenta patent for VIP genes. Mammalian acute toxicity studies

were done using the VIPA3 toxin produced in bacteria, not the toxin produced in

modified corn or cotton. The VIPA3 toxin in cotton is assumed to be

substantially equivalent to the toxin produced in bacteria but, as in the case

of most other commercial Bt cry toxins, the toxin protein is allowed to diverge

significantly from the bacterial toxin so long as the protein

remains active against insect cells and is immunologically similar to the toxin

produced in cotton. The toxin tested by Syngenta showed no overt acute toxicity

and there was no indication that it was allergenic. Sequence analysis showed no

overt similarity to known toxins. The practice of putting forward Bt toxins

produced in bacteria as equivalent to the Bt toxins produced in crops was

criticised earlier. The practice is unsound and should, at least, be made very

clear in the government announcements on the safety testing of GM crops bearing

genes for Bt toxins.

 

The EPA report notes: " Once in the insect gut, the VIPA3 protein binds to

specific receptors (different from those by Cry 1A proteins) and forms ion

specific pores. " There was no discussion, in the EPA report of the apoptosis and

binding to death sequences receptors mentioned in the Syngenta patent. Indeed,

the claim that the VIP3A toxin had no obvious homology to mammalian toxins seems

to have ignored the homology of all apoptosis receptor death sequences. The

contrast between the Syngenta patent and the EPA report is perplexing because

the patent document was well supported with experiments while the EPA report

provided little scientific evidence for its claims.

 

In conclusion, the Bt toxins of the VIP gene family provide potent broad

spectrum insect control. The toxins have been reported to act by binding to

death sequences and triggering apoptosis in insect cells. At the very least, the

potential impact of such toxins on the receptors and death sequences in

mammalian cells should be fully evaluated before GM crops bearing the toxins

enter the mammalian food chain.

 

 

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This article can be found on the I-SIS website at

http://www.i-sis.org.uk/NGMTLOOF.php

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General Enquiries sam

Website/Mailing List press-release

ISIS Director m.w.ho

 

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