Magnetic resonance imaging (MRI) enables high-resolution non-invasive observation of the anatomy and function of intact organisms. However, previous MRI reporters of key biological processes tied to gene expression have been limited by the inherently low molecular sensitivity of conventional 1H MRI. This limitation could be overcome through the use of hyperpolarized nuclei, such as in the noble gas xenon, but previous reporters acting on such nuclei have been synthetic. Here, we introduce the first genetically encoded reporters for hyperpolarized 129Xe MRI. These expressible reporters are based on gas vesicles (GVs), gas-binding protein nanostructures expressed by certain buoyant microorganisms. We show that GVs are capable of chemical exchange saturation transfer interactions with xenon, which enables chemically amplified GV detection at picomolar concentrations (a 100- to 10,000-fold improvement over comparable constructs for 1H MRI). We demonstrate the use of GVs as heterologously expressed indicators of gene expression and chemically targeted exogenous labels in MRI experiments performed on living cells.
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We thank P. Dao for assistance with NMR measurements, M. Cannon for providing the pNL29 plasmid and R. Zalpuri and K. McDonald for assistance with electron microscopy. This work was supported by the Miller Research Fellowship and Burroughs Wellcome Career Award at the Scientific Interface (M.G.S.), California Institute For Regenerative Medicine grant RT2-02022 (D.V.S.) and Department of Energy contract DE-AC02-05CH11231 (A.P., V.S.B).
The authors declare no competing financial interests.
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Shapiro, M., Ramirez, R., Sperling, L. et al. Genetically encoded reporters for hyperpolarized xenon magnetic resonance imaging. Nature Chem 6, 629–634 (2014). https://doi.org/10.1038/nchem.1934
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