A team led by Thomas Meade at the California Institute of Technology has developed an MRI contrast agent that is activated only in the presence of a target gene, according to a report in the March issue of Nature Biotechnology. Unlike conventional light-based detection methods, the new technique is nondestructive to living tissues and makes it possible for the first time to study gene expression occuring deep within live organisms. The contrast agent, known as EgadMe (short for 1-(2-)b-galactopyranosyloxy) propyl-(1,4,7,10-tetraazacyclododecane) gadolinium III) yields a robust MRI signal only when it is exposed to the product of the gene encoding β-galactosidase. To test the system, the authors injected EgadMe into two-celled Xenopus embryos and then introduced nucleic acid encoding β-galactosidase into only one of the two cells. When the fully developed animal was then viewed using an MRI instrument, the tissues derived from the β-galactosidase injected cells produced a high-intensity signal that could be viewed in real time. The authors confirmed that these tissues were actually β-galactosidase expressing cells using a conventional detection system. The new method could provide a powerful tool for studying gene expression patterns in many living systems, from developing embryos to animal models of disease.—Hakon Heimer
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