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Diet containing glyphosate-resistant soybeans affected the nuclei of liver cells in mice.

Manipulated Organism: Soybean (Glycine max).

Inserted Transgenes and Intended Effect: CP4 EPSPS gene derived from the common soil bacterium Agrobacterium sp. Strain CP4. The gene was fused to the cauliflower mosaic virus (CaMV-35S) promoter so that the target gene would be expressed in all parts of the plant. The transgenic soybeans are resistant to glyphosate which is the active ingredient of the herbicide Roundup.

Goal of This Study: Investigation of livers of mice that were fed a diet containing glyphosate-resistant soybeans. The researchers focused on the liver since it is "a primary site for biotransformation of the products of digestion and is strategically located between the intestinal tract and the general circulation. Moreover, it degrades and detoxifies toxic compounds received from the intestines or from the general circulation and excretes them in the bile" ( p.173).

Swiss mice were fed 14% GM soybean in a standard laboratory chow. Control mice were fed on the same diet but with unmodified soybeans. Feeding experiment began with pregnant mice and the offspring were fed for 8 months under constant environmental conditions. Mice were killed and their liver cells investigated when 1, 2, 5 or 8 months old.

Unintended Effects:
  • Electron microscopic examination of liver samples showed that the shapes of the cell nuclei in liver cells differ in GM fed mice and controls: "In fact, except for 1 month-old animals, all GM fed mice showed irregular shaped nuclei, while control animals generally showed roundish nuclei. An irregular nuclear shape generally represents an index of high metabolic rate . . ." (p. 177). The irregular shape appeared as fine waving and increases the surface area between the nucleus and the cytoplasm.
  • Nuclear pores were more frequent in the irregular shaped nuclei of GM fed-mice.
  • In GM fed mice, the nucleoli of liver cells had an irregular shape, numerous small fibrillar centers (FCs), and abundant dense fibrillar component (DFC). "It is known that when the metabolic rate increases the number of small FCs as well as the amount of DFC increase. . . . Interestingly, in our animals the modifications of FC size as well as of DFC . . . amounts are related to food only" (p. 178).
  • Nucleoplasmic (snRNPs and SC-35) and nucleolar (fibrillarin) splicing factors were more abundant in GM-fed mice. Splicing factors play an essential role in the initial stages of gene expression leading to protein formation and enzyme activity.

The authors conclude: "The present work demonstrates that GM soybean intake can influence hepatocyte [liver cell] nuclear features in young and adult mice and, although the mechanisms responsible for such alterations are still unknown, our data encourage further investigations on this subject of relevant scientific interest" (p. 179).

Source: Malatesta, M., C. Caporaloni, S. Gavaudan, M. B. L. Rocchi et al. (2002). “Ultrastructural Morphometrical and Immunocytochemical Analyses of Hepatocyte Nuclei from Mice Fed on Genetically Modified Soybean,” Cell Structure and Function vol. 27, pp. 173-80.

Author Affiliations: University of Urbino, Italy; Instituto Zooprofilattico Sperimentale, Perugia, Italy.

Funding: Not mentioned.

Product Status: Glyphosate-resistant soybeans are commercially grown and have been on the market in the United States since 1996. Most of these soybeans are used for animal feed (cattle, pigs, and chicken).

Copyright 2008 The Nature Institute.

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