Genetically encoded reporters for hyperpolarized xenon magnetic resonance imaging
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 ^(129)Xe 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.
© 2014 Macmillan Publishers Limited. Received 28 May 2013; Accepted 24 March 2014; Published online 28 April 2014. 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). Author contributions: M.G.S. conceived and directed the study. M.G.S., R.M.R., V.S.B. and L.J.S. designed the experiments. M.G.S., R.M.R., J.S. and L.J.S. performed NMR measurements. M.G.S. prepared the GVs, bacteria and mammalian cells. M.G.S. and G.S. generated E. coli genetic constructs. M.G.S., R.M.R. and J.S. analysed the data. M.G.S. wrote the manuscript with interpretation and input from all authors. M.G.S. and V.S.B. provided supervision with input from A.P. and D.V.S. Competing financial interests The authors declare no competing financial interests.
Supplemental Material - nchem.1934-s1.pdf