Photoacoustic imaging of gene expression using tyrosinase as a reporter gene

Optical reporter genes, such as green fluorescence protein, are powerful research tools that allow visualization of gene expression. We have successfully used tyrosinase as a reporter gene for photoacoustic imaging. Tyrosinase is the key regulatory enzyme in the production of melanin which has a broad optical absorption spectrum. MCF-7 cells were stably transfected with tyrosinase under the control of an inducible promoter. For photoacoustic experiments, MCF-7 cells were resuspended at 10 8 cells/mL and injected in 700 μm (inner diameter) plastic tubing. Photoacoustic signal of MCF-7 cells expressing tyrosinase were >20-fold greater than those of untransfected MCF-7 cells. Photoacoustic signal of tyrosinase-expressing MCF-7 cells were approximately 2-fold lesser and greater than those of blood at 576 and 650 nm, respectively, suggesting that photoacoustic signal from blood and tyrosinase-expressing cells can be separated by dual-wavelength analysis. Photoacoustic signal from tyrosinase-expressing MCF-7 cells covered by chicken tissue could even be detected at a laser penetration depth of 4 cm, suggesting that tyrosinase can be used to image gene expression in relatively deep tissues. The current data suggests that tyrosinase is a strong reporter gene for photoacoustic imaging.