Genetically modified foods--safety and regulatory issues.
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The use of chicken blastodermal cells (CBC) in the production of transgenic chickens requires incorporation of the desired stable genetic modification into CBC. With greater proportions of stably transfected blastodermal cells in the embryo inoculum, the frequency of intermediate chimeric birds is greater. Magnetic-activated cell sorting (MACS) was evaluated as a method for enrichment of transfected CBC. This approach requires surface expression of a molecule that can be recognized by an antibody. Chicken blastodermal cells from fertilized Barred Plymouth Rock eggs were coelectroporated with pmiwZ and pMACS Kk and were sorted magnetically by expression of the mouse H-2Kk molecule on the surface of successfully transfected cells. The effectiveness of sorting was assessed using X-gal staining to detect lacZ expression from the pmiwZ plasmid. After 48 h of culture, lacZ-positive cells appeared to be enriched 1.4-fold in the MACS selected population. Cells from this enriched pool contributed to extra-embryonic and intra-embryonic tissues of 72-h White Leghorn recipient embryos with a marginal increase in levels of intra-embryonic contribution. Our demonstration that transfected, cultured, and magnetically sorted CBC maintain their ability to contribute to ectodermal and mesodermal lineages of intra-embryonic tissues illustrates the potential value of this technique for introducing genetic modifications into birds.
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Organisms modified by the techniques of modern biotechnology may differ significantly from normal organisms or organisms modified by other methods. Before transgenic organisms are introduced into the environment, the potential environmental effects should be assessed. In general, modification of ecologically important traits in undomesticated species presents the greatest environmental risk. Transgenic livestock probably pose low risk to the environment. Transgenic fish and live virus-based vaccines pose greater risks and present challenging questions for environmental risk assessment.
Targeted genetic modification of embryonic stem cells (ESC) was used to obtain nondifferentiated cell clones containing the foreign genetic material in the genome. It was demonstrated that transgenic animals may be obtained by ESC injection in preimplantation embryos and subsequent transplantation of the embryos into a recipient female. Using this method, we constructed chimeric animals with a modified genome.