Research papers p. 321--326
MRI reaches the parts other methods cannot reach
Imagine being able to follow the expression of any gene in a living organism no matter where in the organism that gene is located. Scientists have taken the first steps in achieving that goal using a technology termed magnetic resonance imaging (MRI). Their approach can image expression of a marker gene as it occurs deep within the interior of a living animal-a feat previously impossible using other technologies. The authors suggest that the technique could be used to visualize changes in gene expression in a living mouse embryo in utero, providing new insights into the role of particular genes in developmental processes.
Until now, scientists have only been able to visualize gene expression in tissues that can be penetrated by light. Many current confocal microscopy methods also use wavelengths of light that damage cells over time, making the visualization of gene expression in a living embryo impractical over prolonged periods. In contrast, the MRI method can image the expression of genes active deep within an organism and is more suitable for studying live specimens because it is less harmful to cell integrity.
With this in mind, Thomas Meade and colleagues have designed an MRI contrast agent that is activated solely in the presence of a gene of interest. This contrast agent-1-(2-) b-galactopyranosyloxy)propyl)-1,4,7,10-tetraazacyclododecane)gadolinium(III) or EgadMe for short-yields a robust MRI signal only when it is exposed to the product of the gene encoding b-galactosidase. By specifically cleaving a sugar from the EgadMe molecule, b-galactosidase, liberates atoms within EgadME that interact with water molecules and produce a detectable magnetic resonance signal.
To test the system, the authors injected EgadMe into two-celled Xenopus embryos and then introduced nucleic acid encoding b-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 b-galactosidase injected cells produced a high-intensity signal that could be viewed in real time. The authors confirmed that these tissues were actually b-galactosidase expressing cells using a conventional detection system.
Contact
(Author)
Dr. Thomas J. Meade
Biological Imaging Center
Beckman Institute (139-74)
Caltech
Pasadena, CA 91125
Tel: 626-395-2776
Fax: 626-449-5163
[email protected]
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